Category Archives: Pest Alerts

Ralstonia Wilt – Pest Alert

What is Ralstonia wilt?  Ralstonia wilt (also sometimes known as Southern wilt) is a usually lethal disease that affects over 250 plants in over 40 plant families.  Susceptible greenhouse-grown ornamentals include, but are not limited to, plants in the genera Capsicum, Cosmos, Cyclamen, Dahlia, Fuschsia, Gerbera, Hydrangea, Impatiens, Lantana, Nasturtium and Pelargonium.  Vegetables such as eggplant, pepper, potato and tomato, as well as tobacco, are also susceptible.  Ralstonia wilt was first reported on geraniums (Pelargonium spp.) in Wisconsin in 1999.  In 2020, the disease was reported on Fantasia © ‘Pink Flare’ geraniums in Michigan.  Potentially infected ‘Pink Flare’ geraniums were also distributed to 38 other states including Wisconsin.

Yellowing and wilting characteristic of Ralstonia wilt. Photo courtesy of WI DATCP
Yellowing and wilting characteristic of Ralstonia wilt. Photo courtesy of WI DATCP

What does Ralstonia wilt look like? Symptoms of Ralstonia wilt in geraniums are similar to those associated with bacterial blight (caused by Xanthomonas campestris pv. pelargonii).  Initially, lower leaves of infected plants yellow and wilt, then die.  Yellowing and death of upper leaves follow.  Symptoms may initially occur on only one side of the plant.  Internally, the water-conducting tissue of the plant browns, and then the entire stem rots from the inside out.  Eventually, infected plants die.

Where does Ralstonia wilt come from? Ralstonia wilt is caused by the bacterium Ralstonia solanacearum (formerly Pseudomonas solanacearum).  This bacterium is commonly found in tropical, sub-tropical and warm temperate climates, but is not believed to survive cold temperatures such as those typical of Wisconsin winters.  The bacterium can be moved in symptomless plants or cuttings, or in contaminated soil and plant debris (where the pathogen can remain dormant for many years).  Several subgroups (i.e., races and biovars) of R. solanacearum have been recognized, each with a different host range.  R. solanacearum race 3, biovar 2 is of particular concern because it causes a serious disease of potato called brown rot.  In addition, this race/biovar has been listed as a select agent by the U.S. government and is considered to have potential to be developed as a bioterrorist weapon against U.S. agriculture.

How do I save plants with Ralstonia wilt? There are no known treatments that will save plants affected by Ralstonia wilt.  If you believe your plants are suffering from this disease, immediately contact your local department of agriculture or county Extension agriculture or horticulture agent to arrange for confirmatory testing.  If you live in Wisconsin, you can contact the UW-Madison Plant Disease Diagnostics Clinic (see below for contact information) for assistance.  If your plants test positive for R. solanacearum race 3, biovar 2 the United States Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) must be notified and this organization will provide guidance on proper disposal of contaminated plants, as well as decontamination of greenhouses or other sites where contaminated plants have been grown.

How do I avoid problems with Ralstonia wilt in the future? Start by purchasing and growing pathogen-free plant cuttings.  Keep plants from different suppliers physically separated by at least 4 ft. to minimize the risk of cross contamination should a shipment of plants prove to be contaminated.  Because R. solanacearum is easily moved with soil or water, minimize splashing or any other movement of water or soil from plant to plant when watering.  When taking cuttings or trimming plants, be sure to clean cutting tools between cuts using an approved disinfectant.  For a complete list of such products, contact the UW-Madison Plant Disease Diagnostics Clinic (see below for contact information).  Also wear disposable gloves (nitrile are best) when handling plants, and change gloves between working with different geranium varieties.  This will minimize the possibility of moving R. solanacearum by touch.  If gloves are not available, wash your hands frequently and thoroughly (especially between geranium varieties) with lots of soap and water or with an alcohol-based hand sanitizer.  Remove and destroy weeds or weed debris as these can harbor the pathogen.  Finally, do not grow plants in a greenhouse where the disease has occurred unless it has been properly decontaminated.

For more information on Ralstonia wilt or help in diagnosing this problem:  Contact Brian Hudelson, Plant Disease Diagnostics Clinic, University of Wisconsin-Madison, 1630 Linden Drive, Madison, WI  53706-1598 [phone: (608) 262-2863, fax: (608) 263-3322, email:  pddc@wisc.edu.

Professional Guide to Emerald Ash Borer Insecticide Treatments – Pest Alert

Emerald ash borer insecticide treatment considerations.  

A variety of insecticide products and application methods are available to professionals for control of the emerald ash borer (EAB).  Since the presence and infestation level of EAB is quite difficult to determine at early stages of an infestation, insecticide treatments may be merited to mitigate damage by EAB.  However, not all ash trees should be treated as some may be too extensively compromised or in poor condition to receive treatment.  Due to the expense of yearly insecticide treatments, one should consider the value of a particular ash tree in relation to insecticide treatment costs before making any treatments.  In addition, consider the health of each tree before treating.  Research suggests that insecticide treatments are significantly more effective on EAB-infested ash trees with less than 50% canopy thinning.  Insecticide treatments are not suggested for trees with greater than 50% canopy thinning.  Ash trees with greater than 50% canopy thinning should be removed and destroyed in accordance with established state and federal guidelines.  For additional information on this topic, see University of Wisconsin Garden Pest Alert XHT1215, Is My Ash Tree Worth Treating for Emerald Ash Borer.

Emerald ash borer insecticide treatment options. 

Insecticide products that are available for use by professionals, with information on appropriate application methods and application timings, are summarized in Table 1.  These products include:

  • Ace-Jet (acephate)
  • ACECAP Systemic Insecticide Tree Implants (acephate)
  • ArborMectin (emamectin benzoate)
  • AzaGuard (azadirachtin)
  • Boxer Insecticide-Miticide (emamectin benzoate)
  • Brandt enTREE EB (emamectin benzoate)
  • Dinocide, Dinocide HP (dinotefuran)
  • IMA-jet, IMA-jet 10 (imidacloprid)
  • Imicide, Imicide HP (imidacloprid)
  • Inject-A-Cide B (bidrin)
  • Mectinite (emamectin benzoate)
  • Merit 2F, Merit 75 WP, Merit 75 WSP (imidacloprid)
  • OnyxPro (bifenthrin)
  • Pointer (imidacloprid)
  • Safari (dinotefuran)
  • Tempo (cyfluthrin)
  • Transtect (dinotefuran)
  • Tree-äge, Tree-äge G4 (emamectin benzoate)
  • Treeazin (azadirachtin)
  • TreeMec Inject (emamectin benzoate)
  • Xytect 2F, Xytect 75 WSP, Xytect 10% infusible (imidacloprid)

University research indicates that soil drenches or injections of imidacloprid provide excellent EAB protection for small ash trees [less than six inches diameter at breast height (DBH)] in the first year following treatment.  Larger trees may require two consecutive years of treatment before they are effectively protected.  Thus, treatment of large trees should begin before the trees become infested.  While spring and/or fall applications are allowed on certain product labels, recent university research has indicated that spring applications have been more effective at controlling EAB and protecting canopy health.  Most insecticide treatments must be repeated each year.  Products containing emamectin benzoate are labeled to provide two years of protection.  Recent university research suggests that some of these products may provide more than three years of control with a single application when used at the highest labeled rate.

Trunk injections and implants require physically drilling or coring into a tree during the application of the insecticide.  Thus, use of these application methods has the potential to cause injury to trees (especially smaller trees), and may provide entry points for certain disease-causing fungi [e.g., Nectria, the cause of Nectria canker (see University of Wisconsin Garden Facts XHT1094 Nectria Canker)]

Table 1.  EAB insecticide treatments available to professionals*
Active Ingredient Product(s) Timing Application Method
Acephate ACE-Jet Mid-May to mid-June Trunk Injection
Acecap Implants Trunk Implant
Azadirachtin AzaGuard, Treeazin Early/mid-April to
early September
Trunk Injection
Bidrin Inject-A-Cide B Inject when infestation is evident Trunk injection
Bifenthrin OnyxPro Apply prior to or just at the time of adult emerge. Multiple applications may be needed Preventative bark and foliage cover sprays
Cyfluthrin Tempo
Dinotefuran Dinocide, Dinocide HP Late-April to late-May Trunk injection
Safari, Transtect, Zylam Soil drench, trunk spray
Emamectin benzoate ArborMectin, Boxer, Brandt enTREE EB, Mectinite, Tree-äge, Tree-äge G4, Tree-äge R10, TreeMec April to September Trunk injection
Imidacloprid Merit 75 WP, Merit 75 WSP, Merit 2F, Xytect 2F, Xytect 75WSP, and others Mid-April to late-May

and/or

Early-Sept. to mid-October

Soil injection or drench
IMA-jet, IMA-jet 10, Imicide, Imicide HP, Pointer, Xytect 10% Mid-April to mid-May Trunk injection

The University of Wisconsin does not endorse any one specific commercially available insecticide.  Products discussed in this fact sheet have been evaluated in a variety of university research tests on EAB (http://www.emeraldashborer.info/).  No matter which insecticide you use, always read and follow all label instructions.  Avoid skin contact with insecticides and safely store insecticides out of the reach of children.

For more information on controlling emerald ash borer: 

See:

Lily Leaf Beetle – Pest Alert

The lily leaf beetle (LLB), Lilioceris lilii, also known as the red or scarlet lily beetle, is an invasive insect of Eurasian origin.  This insect was first reported in North America in eastern Canada during World War II and was most likely introduced in shipments of plant materials from Europe.  LLB spread to New England in the 1990’s and has been moving westward since that time.  LLB made its first appearance in Wisconsin in 2014 and as of the end of 2019 has been found in 12 counties including Dane, Door, Langlade, Lincoln, Marathon, Oneida, Pierce, Portage, Price, Shawano, Taylor and Wood Counties.

Severe feeding damage from lily leaf beetles on a lily plant (left) and an adult lily leaf beetle (right). Photos courtesy of Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
Severe feeding damage from lily leaf beetles on a lily plant (left) and an adult lily leaf beetle (right). Photos courtesy of Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

LLB can cause significant damage to true lilies (Lilium spp.), including both native and cultivated types, as well as fritllaries (Fritillaria spp.).  LLB can also cause damage, but to a lesser extent, to lily of the valley (Convallaria majalis) and Solomon’s seal (Polygonatum spp.).  LLB does not cause damage to daylilies (Hemerocallis spp.), canna lilies (Canna spp.) or calla lilies (Calla palustris).

Appearance:  LLB adults are bright red and approximately 1/4 inch long, with black legs, head, antennae, and undersides.  When disturbed, LLBs tumble from plants and land upside down on the ground, where they play dead.  Their dark-colored undersides make them hard to spot.  To potentially deter predators, adults squeak if squeezed.

LLB larvae have plump, squishy bodies and are slug-like in appearance.  They tend to be orange or yellowish in color with black heads.  At maturity, larvae can be almost 1/2 inch long.  As a defensive tactic, larvae typically camouflage themselves with their own excrement and can resemble slimy greenish-brown slugs or a mobile pile of animal droppings.

LLB eggs are tiny (less than 1/10 inch long) and reddish in color.  Female LLBs lay the eggs (typically in a batch of a dozen or less) on the underside of leaves in a row parallel to a vein.

Symptoms and Effects:  Both LLB adults and larvae chew irregular holes and notches in lily leaves, stems, and developing buds.  Larvae are the more damaging stage of the insect.  When feeding damage is severe, LLBs can completely defoliate plants and destroy flowers.

Life Cycle:  There is a single generation of LLBs each year, but adults can live for several years.  LLBs overwinter as adults in sheltered places, soil, and plant debris in gardens and wooded areas.

These overwintering sites are not necessarily near lilies or other host plants.  Early in the spring, LLB adults emerge to feed, mate and lay eggs.  Because they are strong fliers, LLBs can disperse over long distances to locate host plants.  Eventually, females lay between 250 and 450 eggs.  Eggs hatch within four to eight days.  Emerging larvae feed for two to three weeks during the spring and early summer.  Engorged larvae eventually drop to the soil to pupate (i.e., transform into adults).  Pupae are bright orange and encased in a white cocoon with black spots.  Adults emerge 16 to 22 days later and feed throughout the rest of the growing season and into the fall.

Lily leaf beetle eggs (left) and a lily leaf beetle larva camouflaged with its own feces. Photos courtesy of Gail Hampshire (left) and Kenneth R. Law, USDA APHIS PPQ, Bugwood.org
Lily leaf beetle eggs (left) and a lily leaf beetle larva camouflaged with its own feces. Photos courtesy of Gail Hampshire (left) and Kenneth R. Law, USDA APHIS PPQ, Bugwood.org

Control:  If you have a small number of lilies, consider hand-picking and crushing adults and larvae or knocking them into a container of soapy water.  Also, crush eggs by hand if you see them.  Repeat this process regularly throughout the growing season.  If LLB becomes a chronic and severe problem, consider replacing your lilies with plants that are not attacked by the insect.

You can also use conventional and organic insecticides to help protect plants from the LLB.  Conventional insecticides containing carbaryl, cyfluthrin, cypermethrin, deltamethrin, lambda-cyhalothrin, permethrin, and zeta-cypermethrin control a broad range of pests, including LLB.  Organic insecticides containing azadirachtin, pyrethrins, or spinosad can also be used, as well as horticultural oils and insecticidal soap.  Make sure that the product that you select is labelled for use on landscape flowers.  Be aware that conventional and organic insecticides can pose risks to pollinators, so follow all directions on the label to minimize risks to bees and other pollinators.

For more information on lily leaf beetle:  Contact your county Extension agent.

Viburnum Leaf Beetle – Pest Alert

The viburnum leaf beetle (VLB), Pyrrhalta viburni, is an invasive insect that feeds exclusively on and can significantly damage Viburnum species.  VLB is native to Europe and was detected in Canada in 1947.  The first report of VLB in the United States was in New York State in 1996.  VLB is now found scattered across much of the northeastern US.  In Wisconsin, an isolated infestation of VLB was discovered in Dane County in 2009, but was successfully eradicated.  In 2014, VLB was detected on a mature viburnum bush in northern Milwaukee County and other nearby infestations were detected in June 2015.  At present, VLB infestations are known from Dane, Iron, Kenosha, Milwaukee, Ozaukee, Racine, Walworth, Washington, Waukesha, and Winnebago Counties.

Viburnum leaf beetles adults (left) and larvae (right). (Photos courtesy of Paul Weston, Cornell University, Bugwood.org)

Appearance: Adult VLB’s are approximately ¼ inch long and yellowish-brown in color. VLB larvae can be up to ⅓ inch long and range in color from yellowish-green to light brown with a series of black spots and dashes on their bodies.

Symptoms and Effects: VLB larvae chew holes in viburnum leaves in the spring creating a lace-like (i.e., skeletonized) pattern.  VLB larvae feed individually or in small groups and can cause significant damage to viburnum shrubs.  This damage can resemble the feeding damage of Japanese beetles (see University of Wisconsin Garden Facts XHT1062 “Japanese Beetle”).  In late June and early July, VLB adults begin to feed, chewing oblong holes in leaves.  Severe VLB infestations can cause complete defoliation of a viburnum shrub, which weakens the plant over time and can eventually lead to death.

Life Cycle: There is only one generation of VLB per year.  VLB’s overwinter as eggs and development from eggs to adults takes approximately eight weeks.  Larvae typically appear in early to mid-May and feed for several weeks, passing through three stages (instars) as they grow.  In early to mid-June, larvae pupate in the soil and adults emerge by late June or early July.  VLB females lay eggs during the summer and into October.  They chew small pits in twigs, deposit five to eight eggs into each pit, and then cover the pits with tiny pieces of chewed wood to protect the eggs.  Each female can deposit up to 500 eggs.  Eggs remain in place through the winter until they hatch the following spring.

Control:

Cultural:  When selecting viburnum plants for the landscape, DO NOT use arrowwood viburnum (Viburnum dentatum), European cranberrybush viburnum (Viburnum opulus), or American cranberrybush viburnum (Viburnum opulus var. americanum) as these types of viburnums are strongly preferred by VLB.  Instead use resistant viburnums such as doublefile viburnum (Viburnum plicatum f. tomentosum), Judd viburnum (Viburnum x juddii), or Koreanspice viburnum (Viburnum carlesii).  In addition, between October and the following spring, examine viburnums for twigs where VLB’s have laid their eggs.  Prune and destroy these twigs to reduce VLB numbers.  During the growing season encourage natural VLB predators in your area (e.g., lady beetles, spined soldier bugs, assassin bugs, green lacewings) that can reduce VLB numbers.

Adult viburnum leaf beetle feeding damage (left) and egg-laying sites (right). (Photos courtesy of Paul Weston, Cornell University, and Bruce Watt, University of Maine; Bugwood.org)
Adult viburnum leaf beetle feeding damage (left) and egg-laying sites (right). (Photos courtesy of Paul Weston, Cornell University, and Bruce Watt, University of Maine; Bugwood.org)

Chemical:  Prior to bud break, apply horticultural oil to twigs where VLB eggs have been laid.  This will significantly reduce the number of eggs that will hatch.  Control any surviving larvae with contact insecticides such as acephate, bifenthrin, carbaryl, cyfluthrin, deltamethrin, lambda-cyhalothrin, and permethrin.  Horticultural oil, insecticidal soap, pyrethrins and spinosad can also be effective.  To achieve the best results, apply insecticides when larvae are small and before they have caused significant damage.  VLB adults can be managed with contact insecticides, if needed, but are mobile and more challenging to control.  Systemic products (e.g., clothianidin and imidacloprid) applied as soil drenches can also be effective, but apply these products after flowering (to minimize any risks to pollinators), but before VLB damage occurs to achieve the best protection.

For more information on viburnum leaf beetle: Contact your county Extension agent.

Sudden Oak Death – Pest Alert

What is sudden oak death?  Sudden oak death (also called Ramorum leaf blight or Ramorum dieback) is an oftentimes lethal disease that has caused widespread death of tanoak (Lithocarpus densiflorus), coast live oak (Quercus agrifolia), California black oak (Quercus kelloggii), and Shreve oak (Quercus parvula var. shrevei) in California.

Rapid wilting and die back of branch tips can be a symptom of ramorum dieback.
Rapid wilting and die back of branch tips can be a symptom of ramorum dieback.

The disease can affect or has been reported in association with a wide range of woody and herbaceous plants including, but not limited to bigleaf maple (Acer macrophyllum), Bodnant viburnum (Viburnum X bodnantense), ‘Brouwer’s Beauty’ pieris (Pieris floribunda X japonica), California bay laurel (Umbellularia californica), California buckeye (Aesculus californica), California coffeeberry (Rhamnus californica), California honeysuckle (Lonicera hispidula), canyon live oak (Quercus chrysolepis), coast redwood (Sequoia sempervirens), doublefile viburnum (Viburnum plicatum var. tomentosum), douglas-fir (Pseudotsuga menziesii var. menziesii), evergreen huckleberry (Vaccinium ovatum), Formosa firethorn (Pyracantha koidsumii), ‘Forest Flame’ pieris (Pieris formosa X japonica), Himalaya pieris (Pieris formosa), Japanese camellia (Camellia japonica), Japanese pieris (Pieris japonica), laurustinus (Viburnum tinus), madrone (Arbutus menziesii), manzanita (Arctostaphylos manzanita), rhododendron (Rhododendron spp.), Sasanqua camellia (Camellia sasanqua), toyon (Heteromeles arbutifolia), western starflower (Trientalis latifolia), and witch hazel (Hamamelis virginiana), Burkwood viburnum (Viburnum X burkwoodii), California hazelnut (Corylus cornuta), Camellia X williamsii, cascara (Rhamnus purshiana), Chinese pieris (Pieris formosa var. forrestii), common lilac (Syringa vulgaris), David viburnum (Viburnum davidii), drooping leucothoe (Leucothoe fontanesiana), European beech (Fagus sylvatica), European cranberrybush viburnum (Viburnum opulus), European turkey oak (Quercus cerris), European yew (Taxus baccata), fragrant viburnum (Viburnum farreri), grand fir (Abies grandis), Holm oak (Quercus ilex), horse-chestnut (Aesculus hippocastanum), lingonberry (Vaccinium vitis-ideae), mountain laurel (Kalmia latifolia), Northern red oak (Quercus rubra), Pieris formosa var. forrestii X Pieris japonica, poison oak (Toxicodendron diversiloba), Prague viburnum (Viburnum X pragense), reticulate camellia (Camellia reticulata), salmonberry (Rubus spectabilis), Southern red oak (Quercus falcata), strawberry tree (Arbutus unedo), sweet chestnut (Castanea sativa), Viburnum X carlcephalum X Viburnum utile, Victorian box (Pittosporum undulatum), wayfaringtree viburnum (Viburnum lantana), and wood rose (Rosa gymnocarpa).

Sudden oak death was first reported in the US in California and has subsequently been found in other US states, including in Wisconsin in 2019.  Sudden oak death has also been reported in Europe.

What does sudden oak death look like?  Symptoms of sudden oak death vary depending upon the plant species infected.  On some hosts, infections occur primarily on leaves leading to light brown leaf spots and blotches.  These leaf symptoms may be indistinguishable from other, more common, leaf spots and blights, or may mimic sunburn or leaf scorch symptoms.  Twigs and branches that become infected often wilt, forming a “shepherd’s-crook”, and subsequently die back.  Infection of tree trunks leads to cankers (i.e., sore-like areas) that produce large amounts of an amber to black colored ooze.  This ooze can dry to form a stained area on the bark.  Removing the bark over the affected area will reveal discolored wood beneath that sometimes (but not always) has a black border.  Cankers can eventually expand to girdle trunks, thus resulting in the death of the tree or shrub.  Trunk infections appear not to extend into the root system of the plant.  Once sudden oak death cankers develop, other pathogens may invade the infected areas, accelerating tree or shrub death and complicating the diagnosis of the disease.

Where does sudden oak death come from?  Sudden oak death is caused by the fungus-like water mold Phytophthora ramorum, which was first recognized as a pathogen in 1995.  Phytophthora ramorum can be spread over long distances through movement of infected plants or infested plant parts.  The organism can also be moved with contaminated soil (e.g., on vehicle tires, tools, or shoes), or in contaminated water.  Once established on plants in a given location, the fungus produces reproductive structures (called sporangia) that can be moved from plant to plant by rain splash, or wind.  Phytophthora ramorum was introducing into Wisconsin in 2019 on nursery stock grown in the state of Washington.

Ramorum leaf blight symptoms can mimic those of other leaf spots and blights.
Ramorum leaf blight symptoms can mimic those of other leaf spots and blights.

How do I save a plant with sudden oak death?  If you believe you have seen a plant that has sudden oak death, please IMMEDIATELY submit a sample to the Plant Disease Diagnostics Clinic (PDDC), care of the address in the box at the bottom of this page.  Double bag suspect plant tissue in sealable plastic bags and place the bagged specimen in a box or envelope for shipping.  Include contact information (complete address, phone number, email address) in a separate sealable plastic bag with the sample.  Tape over all of the edges of boxes and envelopes used for shipping to keep everything sealed inside.  Write on the box or envelope that the box or envelope contains a suspect SOD sample.  If you have questions about collecting or submitting a sample, contact PDDC staff at (608) 262-2863 or at pddc@wisc.edu.

Because Phytophthora ramorum is a regulated, quarantined pathogen, DO NOT remove the affected plant (or parts thereof) or take the plant from the site where it is located, other than to collect a specimen for submission for a diagnosis.  Be sure to decontaminate any tools or other items that come into contact with the plant (including those used to collect a diagnostic sample) by dipping them for at least 30 seconds in 10% bleach.  If a plant tests positive for Phytophthora ramorum, it will be removed and destroyed to help prevent further spread of the pathogen.

How do I avoid problems with sudden oak death in the future?  Carefully inspect any new nursery stock upon delivery (or prior to purchase, if possible) for symptoms of sudden oak death.  Keep new stock isolated from older stock as long as possible, to minimize possible movement of the pathogen should the disease develop after plants have arrived.  If you see any suspect symptoms, alert the PDDC so that arrangements can be made for proper testing for Phytophthora ramorum.

For more information or help in diagnosing sudden oak death:  Contact Brian Hudelson, UW-Madison Plant Disease Diagnostic Clinic, Department of Plant Pathology, University of Wisconsin-Madison, 1630 Linden Drive, Madison, WI  53706-1598, phone: (608) 262-2863, email: pddc@wisc.edu, see the USDA APHIS sudden oak death website https://www.aphis.usda.gov/aphis/ourfocus/planthealth/plant-pest-and-disease-programs/pests-and-diseases/phytophthora-ramorum/sod, or contact your County Extension agent.

African Fig Fly – Pest Alert

The African fig fly (AFF), Zaprionus indianus, is an invasive vinegar fly closely related to flies in the genus Drosophila [which includes the common vinegar fly (also sometimes called the common fruit fly) and spotted-wing drosophila (SWD)].  AFF is native to Africa, Eurasia and the Middle East.  It was first detected in the United States in Florida in 2005, where it is now well established.  In 2012, AFF (a single adult) was first detected in Wisconsin.  In 2017, larger numbers of AFF were found in the state in traps used to monitor for SWD.

An African fig fly adult. (Photo courtesy of Benjamin Davidson)
An African fig fly adult. (Photo courtesy of Benjamin Davidson)

Outside of Wisconsin, AFF has had its biggest economic impact in commercial fig production, and has not been found to have a significant economic impact on other agricultural crops.  In Wisconsin, the potential economic impact of AFF on fruit and other crops is not yet known.  Because AFF reproduces readily and can rapidly expand its range, careful monitoring for this insect in the state is warranted.

Appearance:  The adult AFF is slightly larger than the common vinegar fly or SWD, and has a light-colored body and bright red eyes.  An adult AFF has four black-bordered, white stripes that run along each side of its head and thorax (but not its abdomen).  These stripes can easily be seen using a hand lens and are not found on any other vinegar flies in Wisconsin.  An AFF larva (maggot) is legless and has a single hook-like tooth at its mouth-end.  The maggot uses this tooth to feed on rotted berries and other soft fruit tissues.  AFF maggots are nearly indistinguishable from maggots of common vinegar flies and SWD.

Host Range:  AFF can feed on a large number of fruit crops grown in Wisconsin, including blackberries, blueberries, grapes, peaches, raspberries and strawberries, with grape being a preferred host.

Symptoms and Effects:  Given that AFF is a newcomer to Wisconsin and its temperate climate, predicting which fruits the insect will affect, and to what extent, is difficult.  What is known about AFF is that it cannot initiate damage to intact, ripe fruit; it can only feed on and lay eggs inside of overripe or already damaged fruit.  The insect contributes to additional breakdown and decay of these fruit.  In Wisconsin, AFF and SWD (which can damage intact, ripe fruit) will likely occur together at a given location, and will likely interact.  AFF may end up laying eggs in fruit damaged by SWD, possibly leading to an increase in AFF populations.  The effects of AFF on SWD populations are not clear at this time.  However, some research conducted in grapes suggests that where AFF and SWD occur together, they may compete, leading to increased numbers of AFF and lower numbers of SWD.

Life Cycle:  As an insect native to the tropics, AFF will likely not be able to survive even a mild winter in Wisconsin; in fact, AFF does not appear to overwinter even as far north as Virginia.  However, AFF can travel long distances on air currents, and could potentially travel from the southern US to Wisconsin in the spring and summer, leading to fruit infestations in the state in the summer and fall.  AFF has only been detected in Wisconsin in 2012 and 2017, suggesting that if the insect does cause problems in Wisconsin, these problems will not likely be a yearly occurrence.

Exactly how many generations of AFF might develop in Wisconsin in a given year is not known.  In the laboratory (at 75°F), AFF develops from egg to adult in 20 days and females lay, on average, 60 eggs.  Based on its short generation time and ability to produce numerous eggs, AFF populations could potentially build quickly within a given year, once the insect arrives in Wisconsin.

Monitoring:  Monitor for AFF using the same traps that you would use to monitor for SWD.  You can buy commercially available traps, or alternatively, you can make simple, inexpensive traps using a 32-ounce clear plastic container with a lid.  To allow adult flies to enter the trap, drill or melt ten 3/16 inch diameter holes around the top of the container.  Bait traps with one tablespoon active dry yeast and four tablespoons sugar in twelve ounces of water.  Alternatively, use a two-inch layer of apple cider vinegar in the bottom of the container.

Add one to two drops of unscented dish soap to the trap to break the surface tension of the liquid so that flies are more likely to

A homemade vinegar fly trap made from a 32-ounce clear plastic container with a lid. (Photo courtesy of Emma Pelton)
A homemade vinegar fly trap made from a 32-ounce clear plastic container with a lid. (Photo courtesy of Emma Pelton)

drown.  Hang traps in a shaded plant canopy where fruit is present.  For strawberries, place traps on the ground.  Check traps and replace liquid bait weekly, using a hand lens to identify trapped insects.  Be careful not to pour bait on the ground near the traps as this will confuse flies and reduce the effectiveness of the traps.  DO NOT bother testing fruit directly to determine infestation rates for AFF, as AFF larvae will be indistinguishable from those of other vinegar flies (e.g., common vinegar fly and SWD).

Control:  Because AFF cannot cause damage to sound fruit, and because recorded populations of AFF in Wisconsin have been low, AFF control may not be needed unless/until severe outbreaks occur.  Control methods recommended for SWD will likely also help control AFF.  In particular, cultural practices such as removing all damaged or rotting fruit and then solarizing (heating) or freezing this material to kill fly larvae may slow buildup of AFF at a given location in a given growing season.  However, because AFF is able to move over long distances from areas in the south where it can easily overwinter, reintroduction of the insect will be possible even if you follow strict sanitation practices.

Exclusion netting, which has been used with some success to manage SWD, will likely also help manage AFF.  When using netting, use a mesh size that is 1/32 inch or smaller.  Start using netting after early fruit set (so as not to interfere with pollination), but before fruit begins to ripen.  Make sure the mesh completely covers fruit with no gaps between sheets of netting or at the soil surface.  Any opening can provide an entry point for AFF.

Chemical control for AFF is not currently recommended in Wisconsin.  Observed AFF populations have not been high enough to warrant such treatments.  If spraying for AFF does become necessary, choose insecticides (e.g., spinosyns, carbamates and organophosphates) that also provide control of SWD.  As always, rotate active ingredients that are in different IRAC chemical classes (i.e., have different modes of action) to delay development of insecticide resistance.  For details on IRAC chemical classes, see https://www.irac-online.org/modes-of-action/.  Also, be sure to consider the effects of the products that you select, on non-target insects, particularly beneficial insects such as bees.  Please check the most recent Midwest Fruit Pest Management Guide (see https://learningstore.uwex.edu) for full product recommendations.

If you suspect that you have found an AFF, please contact the University of Wisconsin-Madison Insect Diagnostic Lab at (608) 262-6510, idl@entomology.wisc.edu or http://labs.russell.wisc.edu/insectlab/contact-us/.

For more information on African fig fly, as well as other vinegar flies:  See University of Wisconsin Garden Facts XHT1102 (Fruit Flies in the Home), University of Wisconsin Garden Facts XHT1237 (Spotted Wing Drosophila), or contact your county Extension agent.

Is My Ash Tree Worth Treating for Emerald Ash Borer? – Pest Alert

This factsheet addresses some of the most frequently asked questions regarding the treatment of ash trees for emerald ash borer (EAB), and the removal and disposal of infested trees.

High value ash trees are candidates for treatment for emerald ash borer.
High value ash trees are candidates for treatment for emerald ash borer.

When should I consider treating my ash tree for EAB?Based on current research, EAB treatments are suggested only for ash trees located within 15 miles of a confirmed EAB site, or for trees located within a quarantined area.  Insecticide treatments are not necessary for ash trees located outside of these areas.  Even within the 15-mile radius, not all trees should be treated.  Due to the expense of insecticide treatments for EAB, consider the value of a particular ash tree in relation to insecticide treatment costs before making any treatments.  Proper use of EAB insecticides can help maintain the health of high value ash trees over time.  Lower value ash trees are not ideal candidates for EAB insecticide treatments.

How do I know if my ash tree has value?  Ash trees can be a valuable part of the landscape.  A properly cared for ash tree can increase property value, provide environmental benefits such as runoff and erosion mitigation, and reduce electricity costs by shading a home.  Determining tree value can be subjective.  Qualities to consider when assessing value include (but are not limited to) a tree’s overall health, shape, location with respect to landscape design, and appearance through the seasons, as well as whether or not a tree provides shade.  A healthy ash that is properly located in the landscape, has a nice shape and good fall color, and provides shade has value.  An ash tree that is not healthy due to disease or insects, has poor shape or structural damage, is otherwise unattractive, or is in a bad location (e.g., near a power line) is of lower value.

How do I know if there are ash trees in my area that are infested with EAB?  The Wisconsin Department of Agriculture Trade and Consumer Protection (DATCP) keeps track of EAB infestations in the state.  Visit the Wisconsin DATCP Emerald Ash Borer Resource Guide website (http://datcpservices.wisconsin.gov/eab/) and view the interactive map.  You can also contact your local county UW-Extension office to see if EAB has been found in your area.

How do I know if my ash tree has EAB?  Symptoms of an EAB infestation can include canopy thinning starting in the upper portion of the tree, epicormic sprouting (i.e., formation of sprouts) along the trunk, bark splitting, and woodpecker damage.  These symptoms indicate general tree stress, and can be due to EAB.  However, they also can be caused by diseases or insects other than EAB.  Specific signs of EAB include D-shaped exit holes (~3/16 inch wide) in the bark of the tree, S-shaped larval tunnels and/or larvae (cream colored, up to 1½ inches long) beneath the bark, and adults (metallic green, ~3/8 inch long).  Visit the UW-Madison Emerald Ash Borer in Wisconsin website (https://eab.russell.wisc.edu) for additional information on the symptoms and signs of EAB.

If I decide to treat my ash tree, will I have to treat every year?  In most cases, yes.  Most insecticides registered for EAB management require yearly applications to effectively protect a tree.  Products containing the active ingredient emamectin benzoate, are labelled for two years of protection.  Products containing emamectin benzoate are trunk-injected insecticides intended for use by professional insecticide applicators (e.g., certified arborists).  Such products can effectively protect an ash trees if the tree is treated every other year.

Can I treat an ash myself or do I have to call an arborist?  If your ash is smaller than 47 inches around the trunk at chest height [i.e., 15″ diameter at breast height (DBH)], you may be able to treat your ash tree yourself.  University of Wisconsin Pest Alert XHT1181 (“Homeowner Guide to Emerald Ash Borer Insecticide Treatments”) provides a list of products currently available for homeowner use.  If you decide to treat your own trees, be sure to read and follow all label instructions of the insecticide that you select to ensure that you use the product in the safest and most effective manner possible.

In some situations, hiring a certified arborist to treat your ash tree may be more desirable.  Professionals have access to specialized application equipment and additional insecticides not available to homeowners.  They are also trained to measure trees accurately, and assess the overall health of trees.  The Wisconsin Arborists Association website (http://www.waa-isa.org) has a list of certified arborists in the state.

Note that the University of Wisconsin does not endorse any insecticide products, and does not recommend any professional products over those available directly to homeowners.

Am I allowed to treat an ash tree in my yard between the sidewalk and street?   The answer to this question varies from municipality to municipality.  In many cases, municipalities have treatment or removal and replacement plans already in place.  Contact your local town, village or city to determine an appropriate strategy for protecting your sidewalk trees.

How much does it cost to treat an ash tree for EAB?  A single tree that is 32 inches around at chest height (approximately 10″ DBH) can be treated with a granular or liquid soil drench homeowner product for about $20-35/year.  Larger trees will require a larger amount of product and costs will be higher.  Arborist treatment costs vary depending on tree size and location, the insecticide selected, and the application method.  Other arborist-specific site visit charges may apply as well.  Consult at least two arborists in your area to discuss treatment options and costs.  To make an accurate comparison among service providers, make sure you know what insecticide will be used, the method of application, and how often treatments will be made.  An arborist will not be able to determine the exact cost of treatment for your specific ash tree without a site visit, but an arborist should be able to provide you with a cost estimate for a typical ash tree.

Do I have to remove my ash tree if it is infested with EAB?  Applying protective insecticide treatments to a healthy ash tree to prevent an EAB infestation is the best strategy for managing EAB.  However, if a tree becomes infested and the infestation is detected early, you may be able to treat your ash tree to prevent further damage, and help the tree recover.  Research suggests that insecticide treatments are significantly more effective on EAB-infested ash trees with less than 50% canopy thinning.  Insecticide treatments are not recommended for trees with greater than 50% canopy thinning; these trees should be removed.  Trees that become infested with EAB and are not treated will ultimately die and will need to be removed.

How much does it cost to remove an ash tree?  Typically, a small (less than 25 feet in height) ash tree may cost a few hundred dollars to be removed by an arborist.  Larger trees may cost $1,000 or more to be removed.  Individual factors (e.g., the proximity of the tree to structures, power lines, or other hazards) can significantly increase the cost of removal.  Tree removal costs also may vary from location to location in Wisconsin.  Ultimately, removing recently killed trees while they are structurally sound, rather than allowing them to deteriorate, may be safer and more cost effective.

How do I dispose of wood from an infested ash tree?  If you choose to remove an infested ash tree, check with your municipality to see if a wood disposal or utilization program is in place.  If you have a tree removed by a tree care service, the service may be able to handle the disposal of wood from the infested tree.  If you decide to use wood from an ash tree for firewood or other purposes, use it locally.  Transporting infested wood risks spreading EAB elsewhere in the state, and may be in violation of Wisconsin’s quarantine laws.  Information about Wisconsin’s firewood regulations can be found on the Wisconsin DATCP Emerald Ash Borer website (http://datcpservices.wisconsin.gov/eab/).

For more information on controlling emerald ash borer: 

Homeowner Guide to Emerald Ash Borer Insecticide Treatments – Pest Alert

Emerald ash borer insecticide treatment considerations.  Several insecticide products are available to homeowners for control of emerald ash borer (EAB).  Since the presence and infestation level of EAB is quite difficult to determine at early stages of an infestation, insecticide treatments may be merited to mitigate damage by EAB.  However, not all ash trees should be treated as some may be too extensively compromised or in poor condition to receive treatment.  Tree location, value, and health, as well as the cost of treatment are all factors to consider.  Due to the expense of yearly insecticide treatments, one should consider the value of a particular ash tree in relation to insecticide treatment costs before making any treatments.  In addition, consider the health of each tree before treating.  Research suggests that insecticide treatments are significantly more effective on EAB-infested ash trees with less than 50% canopy thinning.  Insecticide treatments are not suggested for trees with greater than 50% canopy thinning.  Trees with greater than 50% canopy thinning should be removed and handled in accordance with local guidelines.  For a more detailed discussion on this topic, see University of Wisconsin Garden Facts XHT1215, Is My Ash Tree Worth Treating for Emerald Ash Borer.

Emerald ash borer insecticide treatment options.  Insecticide products available for use by homeowners are summarized in Table 1.  They include:

  • ACECAP 97 Systemic Insecticide Tree Implants (acephate)
  • Bayer Advanced 12 Month Tree and Shrub Insect Control II (imidacloprid)
  • Bayer Advanced 12 Month Tree and Shrub Protect & Feed (imidacloprid)
  • Bayer Advanced 12 Month Tree and Shrub Protect & Feed II (imidacloprid + clothianidin)
  • Bonide Annual Tree & Shrub Insect Control with SYSTEMAXX (imidacloprid)
  • Compare N Save Systemic Tree & Shrub Insect Drench (imidacloprid)
  • Ferti-lome Tree and Shrub Systemic Drench (imidacloprid)
  • Monterey Once a Year Insect Control II (imidacloprid)
  • Optrol (imidacloprid)
  • Ortho Tree & Shrub Insect Control Granules (dinotefuran)
  • Several other products containing imidacloprid are also currently available

Most of the products available to homeowners are systemic insecticides containing imidacloprid and are applied as soil drenches around the base of an ash tree.  A few granular products are also available.  Recent university research suggests that applications of imidacloprid should be made in spring to be most effective.  Research also has demonstrated that soil applications of imidacloprid-containing homeowner products provide excellent EAB protection for ash trees that are less than about 47 inches in circumference [i.e., 15 inches in diameter at breast height (DBH)].  Due to differences in application rates and label restrictions, treatment by a tree care professional (e.g., arborist) may be the best option for larger trees.  For best results, treatment of trees should begin before trees become infested.  Lastly, insecticide treatments must be repeated each year to maintain the health of ash trees.

Be aware that many insecticide products available at hardware stores and garden centers look alike.  Carefully check all product labels before purchase to make sure that you have selected the correct product/active ingredient.  ALWAYS read and follow the pesticide label directions on the product that you select!

Finally, note that although ACECAP 97 Systemic Insecticide Tree Implants are available to homeowners, we do NOT recommend that homeowners use these because they require physically drilling into a tree during their application.

Table 1

Emerald ash borer insecticide treatments available to homeowners

Product Active Ingredient Timing Type of application
Ortho Tree & Shrub Insect Control Granules (G) Dinotefuran Early-June to mid-June Granule (G)
Bayer Advanced 12 Month Tree & Shrub Insect Control II (D)

 

Bayer Advanced 12 Month Tree & Shrub Protect & Feed (D or G)

 

Bonide Annual Tree & Shrub Insect Control with SYSTEMAXX (D)

 

Compare N Save Systemic Tree & Shrub Systemic Insect Drench (D)

 

Ferti-lome Tree & Shrub Systemic Drench (D)

 

Monterey Once a Year Insect Control II (D)

Imidacloprid Mid-April to mid-May Soil Drench (D)

or

Granular (G)

Optrol (D) Imidacloprid Mid-April to mid-May

and/or

Early-Sept. to mid-Oct.

Soil drench (D)
Bayer Advanced 12 Month Tree & Shrub Protect & Feed II (D) Imidacloprid

+

Clothianidin

Mid-April to mid-May Soil Drench (D)
ACECAP 97 Systemic Insecticide Tree Implants Acephate Mid-May to mid-June Trunk Implant

Other emerald ash borer treatment options.

Homeowners may also contact a certified arborist or certified pesticide applicator to treat their trees.  See http://www.waa-isa.org for a list of certified arborists in Wisconsin.  Professionals have access to some products that are not available to homeowners.

The University of Wisconsin does not endorse commercially available insecticide products over those available directly to homeowners.  Products discussed in this fact sheet have been evaluated in university research tests on EAB.

For more information on controlling emerald ash borer:   See:
http://labs.russell.wisc.edu/eab/
http://www.emeraldashborer.wi.gov or
http://www.emeraldashborer.info or contact your county Extension agent.  For a video demonstration of treating your ash trees using a systemic drench, see
http://labs.russell.wisc.edu/eab/2014/07/12/protecting-your-tree-from-the-emerald-ash-borer/.

Boxwood Blight – Pest Alert

What is boxwood blight?  Boxwood blight (also known as box blight and boxwood leaf drop) is a devastating disease of boxwood (Buxus spp.) that can cause leaf loss and eventual death of affected shrubs.  Boxwood shrubs are commonly grown as hedges and as individual plants in home landscapes and public gardens.  Boxwood blight can

Boxwood blight can cause severe leaf loss and eventual death of boxwood shrubs. (Photo courtesy of David Clement, University of Maryland Extension)
Boxwood blight can cause severe leaf loss and eventual death of boxwood shrubs. (Photo courtesy of David Clement, University of Maryland Extension)

affect any type of boxwood (Buxus spp.) including European or common boxwood (Buxus sempervirens)Korean littleleaf boxwood (B. sinica var. insularis), and Japanese littleleaf boxwood (B. microphylla var. japonica).  In addition, the disease has been reported on Japanese and Allegheny pachysandra (Pachysandra terminalis and Pachysandra procumbens respectively), two common groundcovers.  Boxwood blight has been found in Europe and New Zealand, and was first confirmed in the U.S. in 2011.  The disease was first detected in Wisconsin (in Kenosha County) in 2018.

What does boxwood blight look like?  Initially, brown spots appear on the leaves.  The spots eventually enlarge and merge together.  Infected leaves turn brown and fall off.  Boxwood blight can cause total leaf loss on a shrub within days of the first onset of symptoms.  Dark brown to black sunken areas can also form anywhere on the stems, leading to branch dieback  Boxwood blight often kills plants shortly after all of the leaves drop.  Damage from winter burn (see University of Wisconsin Garden Facts XHT1239, “Winter Burn”), dog urine and other diseases such as Volutella blight (see University of Wisconsin Garden Facts XHT1191, “Volutella Blight”) may look superficially similar to symptoms of boxwood blight.

Where does boxwood blight come from?  Boxwood blight is caused by the fungus Calonectria pseudonaviculata (sometimes referred to as Cylindrocladium pseudonaviculatum or Cylindrocladium buxicola) which thrives in humid, warm conditions.  The fungus is typically introduced into any area on nursery plants that are infected, but not showing symptoms.  Holiday wreaths containing boxwood sprigs have also been documented as a source of the boxwood blight fungus.  Once the fungus has been introduced into the landscape, spores can be easily spread by splashing water (e.g., rain or sprinklers), wind or contaminated gardening tools (e.g., pruners, shovels, gloves).  The boxwood blight fungus can survive and produce spores in dead boxwood leaves and branches (including those that have fallen onto the ground) for several years.

How can I save a plant with boxwood blight?  Because boxwood blight is new to Wisconsin and relatively rare, eradicating the causal fungus may be possible.  Therefore, if you find boxwood blight, remove and destroy any affected shrubs.  Currently, free testing for boxwood blight is available through the UW-Madison Division of Extension Plant Disease Diagnostics Clinic (https://pddc.wisc.edu/).  Plants (roots and all) confirmed to have boxwood blight, as well as any leaves or branches that have fallen from these plants, should be removed and destroyed by burning, deep burying (at least two feet deep) or double bagging (in plastic garbage bags), then landfilling.  DO NOT compost any parts of infected shrubs.  Thoroughly decontaminate any tools used in the removal process by dipping them for at least 30 seconds in 70% alcohol (e.g., rubbing alcohol) or (as a last resort) in 10% bleach.  Spray disinfectants that contain at least 70% alcohol also can be used.  Spray tools until they drip and then allow them to air dry.

How can I avoid problems with boxwood blight in the future?  Consider using shrubs other than boxwood in your landscape.  If you decide to use boxwood, choose boxwood blight resistant varieties where possible.  In Wisconsin, hybrid boxwood ‘Green Gem’, common boxwood variety ‘Katerberg’ North Star®, and Korean littleleaf boxwood varieties ‘Eseles’ Wedding Ring®, ‘Franklin’s Gem’, ‘Winter Gem’ and ‘Wintergreen’ are hardy (to USDA hardiness zone 5) and have been documented to be resistant to box blight.  Always buy boxwood shrubs from local reputable suppliers who have thoroughly inspected boxwood plants for evidence of boxwood blight.  Isolate new boxwood shrubs from established boxwoods for several weeks before planting, as

boxwood blight symptoms not become apparent until weeks after purchase.  DO NOT plant boxwoods in areas where boxwood blight has been a problem in the past, as the fungus can survive in boxwood debris (e.g., leaves and branches) for several years.  When planting, space boxwood plants far enough apart from each other, as well as other shrubs, so that branches on adjacent shrubs do not overlap.  This will increase air flow between plants and promote a drier environment that will be less favorable for boxwood blight.  Avoid watering plants with sprinklers or overhead with hoses; instead use a soaker or drip hose.  This will limit splash of spores from plant to plant and also promote a drier environment that is less favorable for disease.

Leaf spots typical of boxwood blight on boxwood sprigs in a holiday wreath. (Photo courtesy Purdue PPDL)
Leaf spots typical of boxwood blight on boxwood sprigs in a holiday wreath. (Photo courtesy Purdue PPDL)

Be cautious when buying holiday wreaths or other garlands.  Avoid holiday decorations that contain boxwood, whenever possible.  If you are unsure whether a wreath that you have purchased contains boxwood, assume that it does and dispose of it appropriately by burning, deep burying or double bagging and landfilling as described above.  Be careful to collect and dispose of any leaves or branches that may have fallen from wreaths as well.  Make sure that no potentially contaminated materials end up near boxwood shrubs in your yard.  Under NO circumstances should you attempt to compost any suspected boxwood materials.

Once boxwood blight has been reported near your location, you may want to consider using preventative fungicide treatments for management.  Fungicides containing chlorothalonil (alone or in combination with thiophanate-methyl or tebuconazole), fludioxonil, metconazole, and tebuconazole (as a stand-alone product) have been shown to provide good control of boxwood blight if applied prior to the development of any symptoms.  These fungicides will not cure existing disease.  If you decide to use fungicides, you will need to treat every seven to 14 days throughout the growing season.  DO NOT use fludioxonil, metconazole, or tebuconazole as the sole active ingredient for all treatments.  If you decide to use one of these active ingredients, alternate its use with at least one of the other active ingredients listed above (except DO NOT alternate metconazole and tebuconazole as these products are chemically related).  Alternating active ingredients will help minimize problems with fungicide-resistant strains of the boxwood blight fungus.  Be sure to read and follow all label instructions of the fungicide(s) that you select to ensure that you use the product(s) in the safest and most effective manner possible.

Finally, routinely (e.g., weekly) check boxwood plants for boxwood blight.  Immediately remove any symptomatic plants and fallen leaves and branches, and dispose of them as described above.

For more information on boxwood blight:  Contact your county Extension agent.

Blueberry Maggot – Pest Alert

Blueberry maggot was first detected in Wisconsin in the summer of 2016 in Adams and Sauk Counties.  This pest feeds inside blueberry fruit and caused damage in commercial blueberry production in the eastern and southern United States, as well as in eastern Canada.  This insect is expected to eventually have a significant impact on blueberry production in Wisconsin.

Blueberry maggot adult with characteristic wing patterns (left) and larva (right). (Photos courtesy of Rufus Isaacs, Michigan State University)
Blueberry maggot adult with characteristic wing patterns (left) and larva (right). (Photos courtesy of Rufus Isaacs, Michigan State University)

Appearance:  The adult blueberry maggot is a fly that is approximately 3/16 inch long and resembles a small housefly, but with dark bands on its wings.  Larvae (or maggots) are legless and can grow up to 5/16 inch in length.  Each larva has a single hook-like tooth at its mouth end.  Blueberry maggots are very similar in appearance to the closely related apple maggot, with adults of both being virtually identical in size and appearance (including wing patterns).  However, apple maggot does not feed on blueberries.

Host Range:  Blueberry (Vaccinium corymbosum) is the only commercially-grown fruit crop affected by blueberry maggot.  Wild hosts include plant species in the genera Vaccinium and Gaylussacia including wild blueberries, lingonberry, dangleberry, deerberry and huckleberry.

Symptoms and Effects:  A single larva feeds inside each fruit causing the berry to become soft as it develops.  Damage may go unnoticed until after harvest, when maggots crawl out of fruit and become visible among fresh fruit or in processed blueberry products (e.g., jams, preserves, pie fillings).

Life Cycle:  Adult blueberry maggots begin to fly in June or July, and continue to fly through August.  Females feed and mate for at least one week before they move to blueberry plants to begin laying eggs.  Females lay a single egg under the skin of a nearly ripe blueberry fruit and can lay up to 100 eggs during their approximately one month-long life span.  Eggs hatch within one week and damage from larvae generally first appears in mid-July, continuing until blueberries have been harvested.  Each maggot feeds in a single blueberry during its two- to three-week development.  After completing their development, larvae drop to the ground and overwinter as pupae in the upper few inches of soil.  A distinctive characteristic of the blueberry maggot is that, although most pupae develop to form adults by the following spring (completing one generation of the insect in a year), some pupae remain underground and do not mature for two or three years.

Monitoring:  Monitor for blueberry maggot adults several weeks before blueberries begin to ripen (usually in early June) using yellow sticky cards impregnated with a feeding attractant (ammonium acetate or ammonium carbonate).  You can buy cards that are pretreated with the attractant, or buy the cards and attractant separately and apply the attractant yourself.  Fold the sticky cards in a V-shape with the yellow side facing down and put up two traps for every five acres.  Because blueberry maggot is currently not widespread in Wisconsin, you can check cards weekly until you find the first adult.  After this initial find, check cards every few days.  Once you find an average of greater than one adult per trap for several days in a row, begin chemical treatments (see below).  Note that the feeding attractant is not specific for blueberry maggot, so you may find other types of flies on the cards – use a hand-lens or magnifying glass to positively identify any blueberry maggot adults.  Remember that blueberry maggot and apple maggot look very similar, but that apple maggot does not feed on blueberries, so flies trapped in blueberry fields/patches are most likely to be blueberry maggot.

Once you have detected adults, you can also test fruit for the presence of larvae.  Collect 100 berries from throughout your planting.  Then break the skins of the berries and mix the berries with a salt-water solution (1 part salt to 4 parts water).  Larvae will float to the surface.  The number of larvae you find represents the percentage of fruit infested.

Control:  Cultural control methods can be useful in preventing blueberry maggot infestations.  Remove weeds to eliminate habitat for blueberry maggot.  Remove wild blueberry and huckleberry plants as these can serve as alternate hosts for the insect.  Harvest fruits thoroughly and heat (to at least 120°F) or freeze any damaged or unusable fruits to kill blueberry maggot larvae.  This is particularly important if you compost fruit, because blueberry maggot pupae can readily survive in compost and serve as a source of an infestation in future years.  Clean soil thoroughly from equipment or beehives that might be moved between blueberry patches.  Blueberry maggot pupae can easily be moved in soil.

A blueberry maggot trap. (Photos courtesy of Rufus Isaacs, Michigan State University)
A blueberry maggot trap. (Photos courtesy of Rufus Isaacs, Michigan State University)

As noted above, start chemical control once you find an average of greater than one adult blueberry maggot per trap for several days in a row.  Alternatively, if you have had a serious problem in the past, you may want to start sprays one week after you trap your first blueberry maggot fly.  Continue sprays every seven to 10 days through harvest.  Some reduced risk active ingredients, such as novaluron, spinetoram, and spinosad are most effective when used as soon as flies are found in traps.  In addition, consider choosing a product that also provides control of spotted wing drosophila, another serious blueberry pest (see University of Wisconsin Garden Facts XHT1237 for details).  Spinosyn, spinetoram, diamide, carbamate, pyrethroid, and organophosphate-containing insecticides are effective against both insects.  Be sure to rotate use of at least two active ingredients with different modes of action to help delay development of insecticide resistance (see http://www.irac-online.org/modes-of-action/ for details), and be sure consider the effects of sprays on non-target (e.g., beneficial insects).  Finally, because you will be spraying ripe berries, pay particular attention to the pre-harvest interval when choosing insecticides.  Check the most recent Midwest Fruit Pest Management Guide (see https://learningstore.extension.wisc.edu/products/midwest-fruit-pest-management-guide20192020-p1785?_pos=1&_sid=1521576f7&_ss=r) for complete product recommendations.

For more information on or help diagnosing blueberry maggot:  Contact your county Extension agent.