All posts by hudelson

Disease - Broad Leafed Woody Ornamental, Disease - Fruit Crop, Disease - Herbaceous Ornamental, Disease - Vegetable

Foliar Nematodes

July 23, 2015 hudelson

UW Plant Disease Facts

Authors: Megan Meyers* and Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 03/01/2024

D-number: D0053

Angular dead areas on Brunnera leaves typical of infections by foliar nematodes. (Photo courtesy of Monica Lewandowski, The Ohio State University Plant Pathology)

What are foliar nematodes?

Foliar nematodes are microscopic worm-like organisms in the genus Aphelenchoides. They live in and on the leaves (and other above-ground plants parts) of over 450 plant species in more than 75 plant families. They are commonly found on hostas, but can affect other herbaceous ornamentals (e.g., African violet, anemone, begonia, chrysanthemum, fern, orchid, veronica) and woody ornamentals (e.g., azalea, elm, privet), as well as fruit crops (e.g., sour cherry, strawberry) and vegetable crops (e.g., broccoli, celery, lettuce, onion, pinto bean, potato, squash, tomato). Damage from foliar nematode is usually cosmetic and non-lethal making ornamental plants less attractive and less saleable. In severe cases and on particularly susceptible hosts (e.g., strawberry), foliar nematodes can cause extensive leaf injury and defoliation, and can interfere with and limit flowering.

What does foliar nematode damage look like?

Unlike most other nematodes, which cause root damage, foliar nematodes cause damage to above-ground plant parts, especially leaves. In young plants, foliar nematodes can cause new growth to curl, twist, and stunt. In more mature plants, foliar nematodes cause small, discolored, angular (i.e., straight-edged) blotches on leaves. The blotchy areas are typically bordered by veins. Blotches eventually turn brown and dry, and may fall away, giving the leaf a “shot-holed” appearance. Angular blotches often are not apparent until late in the growing season (e.g., August).

Where do foliar nematodes come from?

Foliar nematodes are typically first introduced into a garden on infected/infested plants brought from another location. Foliar nematodes can then be spread from infected/infested plants to healthy plants by water splash from rain or overhead watering. Infections most often occur during periods of high humidity or when films of water form on leaves allowing for nematode movement. Foliar nematodes can also be spread when infected/infested plants are vegetatively propagated (i.e., when cuttings are taken from infested plants). Foliar nematodes can survive in dry leaves, dormant buds, and in soil, but not in plant roots. They can survive in unfavorable (e.g., dry or freezing) conditions and quickly become active when moisture becomes available.

Striped dead areas on hosta leaves typical of infections by foliar nematodes.

How do I save a plant with foliar nematodes?

Eliminating foliar nematodes is virtually impossible. No chemical products are available for foliar nematode control in home gardens. Hot water treatments have been developed to treat high-value plants but are not recommended for home gardeners. Exact temperatures/timings for these treatments vary depending on the type of plant being treated, and missteps in timing/temperature can either kill plants or can lead to less than 100% control of the nematodes. If you have plants infected with foliar nematodes, the best course of action is to dig them up, bag them and remove them from your garden as soon as you notice symptoms to reduce the risk of the nematodes spreading to healthy plants. After working with infected plants, wash your hands with soap and water and decontaminate anything that has come into contact with the plants (e.g., tools, pots, bench surfaces, etc.) for 30 seconds with either 70% alcohol (e.g., rubbing alcohol, certain spray disinfectants) or 10% bleach. If you use bleach, be sure to thoroughly rinse and oil metal tools to prevent rusting. Because soil is virtually impossible to decontaminate, avoid planting susceptible hosts in an area where foliar nematodes have been a problem.

How do I avoid foliar nematode problems in the future?

The easiest way to avoid problems with foliar nematodes is to not bring them into your garden. Carefully inspect plants for nematode symptoms before purchase, but keep in mind that plants may not show symptoms early in the growing season. Avoid using overhead sprinklers, as watering in this manner can splash foliar nematodes from plant to plant and promote spread. Instead use a soaker or drip hose that applies water directly to the soil, rather than onto leaves. Space plants far enough apart so that potential spread via water splash during natural rains is minimized, and avoid working with plants when they are wet. DO NOT use foliar nematode-infected plants or even healthy-looking plants suspected to be infested with foliar nematodes when taking cuttings to propagate plants.

For more information on foliar nematodes:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

*Completed as partial fulfillment of the requirements for a BS in Plant Pathology at the University of Wisconsin Madison.

An EEO/Affirmative Action employer, University of Wisconsin-Madison Division of Extension provides equal opportunities in employment and programming, including Title IX and ADA requirements. This document can be provided in an alternative format by calling Brian Hudelson at (608) 262-2863 (711 for Wisconsin Relay).

References to pesticide products in this publication are for your convenience and are not an endorsement or criticism of one product over similar products. You are responsible for using pesticides according to the manufacturer’s current label directions. Follow directions exactly to protect the environment and people from pesticide exposure. Failure to do so violates the law.

Thanks to Bryan Jensen, Anette Phibbs and Ken Williams for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Broad Leafed Woody Ornamental, Disease - Fruit Crop

Fire Blight

July 23, 2015 hudelson

UW Plant Disease Facts

Authors: Ann Joy and Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 03/01/2024

D-number: D0052

What is fire blight?

Fire blight is the most destructive bacterial disease affecting plants in the rose family, including apple, pear, crabapple, hawthorn, cotoneaster, mountain ash, quince, rose, firethorn (Pyracantha), and spirea. It can disfigure or kill a tree or shrub, depending on the susceptibility of the host and weather conditions.

A shepherd’s crook at the end of an apple branch caused by fire blight.

What does fire blight look like?

Blossoms, leaves, twigs, and branches of plants affected by fire blight can turn dark brown to black, giving them the appearance of having been scorched in a fire. Blighted blossoms and leaves tend to stay on the tree instead of falling. The current year’s twigs often wilt and bend approximately 180°, forming a “shepherd’s crook.” Cankers (sunken, discolored areas) form on branches and stems, and emit a sticky bacterial ooze. Sapwood under the bark around cankers can become reddish brown in color. Fruits can develop brown, sunken or shriveled areas that can be sticky.

Where does fire blight come from?

Fire blight is caused by the bacterium Erwinia amylovora, which overwinters on the margins of branch cankers and starts to multiply when temperatures rise in the spring. A bacterium-laden ooze seeps from cankers, and splashing rain and insects disperse this material. In particular, pollinators such as honeybees can feed on the ooze and then transport the fire blight bacterium to flowers as they collect pollen. The fire blight bacterium multiplies in blossoms and eventually can spread to other plant parts where it penetrates through wounds and natural openings. Once the bacterium enters a plant, it can spread rapidly through the plant’s water-conducting (vascular) system.

How do I save a plant with fire blight?

There is no cure for fire blight, but its spread can be limited by pruning out diseased branches. Because the fire blight bacterium can spread rapidly, prune as soon as possible after symptoms become visible. Prune when branches are dry and when your local weather service predicts several days of dry weather. When removing diseased branches, prune at least 12 inches below tissue showing visible symptoms. Always disinfect pruning tools after each cut by treating them for at least 30 seconds with bleach [diluted to a final concentration of approximately 0.5% sodium hypochlorite (the active ingredient)] or (preferably) 70% alcohol (e.g., rubbing alcohol, certain spray disinfectants). If you use bleach, be sure to thoroughly rinse and oil your tools after pruning to prevent rusting. Burn or bury pruned branches.

How do I avoid problems with fire blight in the future?

By far the most effective strategy is to choose plants with fire blight resistance. Also, select a well-drained site with a soil pH of 5.5 to 6.5. Avoid applying high levels of nitrogen fertilizer, as this may stimulate new, succulent growth that is more prone to damage and thus infection. Consider treating with Bordeaux mixture (copper sulfate + lime) before buds open to reduce the level of the fire blight bacterium present on branches. Make one or two applications, with four days between applications.

For more information on fire blight:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

Thanks to Teryl Roper, Patricia McManus, and Patti Nagai for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Field and Forage

Ergot

July 23, 2015 hudelson

UW Plant Disease Facts

Authors: Sarah Rosenthal*, UW-Plant Breeding and Genetics Dan Undersander, UW-Madison Agronomy Damon Smith, Craig Grau and Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0050

Production of honeydew (red arrow) and sclerotia (white arrows) are typical of ergot.

What is ergot?

Ergot is a fungal disease of worldwide distribution that is common in the northern two-thirds of North America. Ergot affects wild and cultivated grasses, as well as small grain crops such as wheat, oats, barley and especially rye. The ergot pathogen produces alkaloid toxins, many of which reduce blood flow in animals (e.g., cattle, sheep, swine, horses and even humans) that eat ergot-contaminated grain. Ergot poisoning is cumulative. Symptoms can develop rapidly if animals eat large quantities of ergot or more slowly if they eat small quantities of ergot on a regular basis. In many animals (e.g., cattle), the first symptom of ergot poisoning is lameness that occurs two to four weeks after ergot is first eaten. Gangrene in extremities (e.g., hooves and ears) follows. Dairy cows that eat ergot-contaminated grain typically have a marked reduction in milk yield. Other symptoms of ergot poisoning can include convulsions, hallucinations and death. Symptom development is often more severe in very hot or very cold weather. Interestingly, some ergot toxins, when purified and used at low dosages, have pharmaceutical applications (e.g., inducing labor and treating migraine headaches).

What does ergot look like?

Signs of ergot first appear as droplets of a sticky exudate (called honeydew) on immature grain heads. Honeydew contains asexual spores of the ergot fungus. Over 40 species of insects are attracted to honeydew and can carry spores from infected to healthy plants. After approximately two weeks, infected grains are replaced by dark (often purplish), compact fungal structures called sclerotia. Sclerotia range in size from ¹/₁₆ to ¾ inches in length, and often look like seeds, rodent droppings, or insect parts.

Where does ergot come from?

Ergot is caused by several species of the fungus Claviceps, most commonly Claviceps purpurea. Sclerotia of these fungi survive in soil and harvested grain. Sclerotia require a one to two month period of cold temperatures (32 to 50°F), after which they germinate to form small, mushroom-like structures that produce sexual spores (different from those produced in honeydew). Germination occurs most commonly in cool (57 to 84°F), damp weather and is inhibited at higher temperatures. Sexual spores are blown to developing grain heads where infection occurs. Humid weather (> 90% relative humidity) contributes to honeydew production. Ergot is also often more severe if frosts occur at the time of spore production.

Ergot sclerotia germinate to form mushroom-like, spore-producing structures.

How can I save a small grain crop with ergot?

Fungicide treatments are not recommended to control ergot. When ergot is a problem, you can attempt to remove sclerotia from grain using commercial seed-cleaning equipment. However, if sclerotia are broken or are the same size as the grain itself, this may be difficult and costly, and may still result in grain that has a contamination level that is above marketable thresholds (tolerance for ergot sclerotia in harvested grain can be as low as 0.05% by weight). Ultimately destroying the contaminated grain may be the best course of action. Be sure to also destroy the hay from the affected field. DO NOT use the hay as feed or for animal bedding.

How can I avoid problems with ergot in the future?

Maintain a rotation with at least one year between small grain crops. Use crops that are not susceptible to ergot (e.g., soybeans, alfalfa, corn) in years when small grains are not grown. Plant grain seed that is free of ergot sclerotia. Ergot-resistant varieties are not available, but avoid longer-flowering varieties as they tend to be more susceptible to infection. Keep weed grasses under control. Also, mow areas adjacent to small grain fields to prevent grasses from flowering and developing ergot. In fields where ergot becomes a problem, consider clean, deep plowing that will bury ergot sclerotia to at least three to four inches, thus preventing sclerotia from germinating. Mow, remove and destroy ergot-infected grasses from pastures and hayfields. DO NOT allow animals to graze in these areas and DO NOT use the harvested material for feed or as bedding material.

For more information on ergot:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

*The original version of this fact sheet was completed as partial fulfillment of the requirements for Plant Pathology 559 – Diseases of Economic Plants at the University of Wisconsin Madison.

Thanks to Diana Alfuth, Bryan Jensen and Kevan Klingberg for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional agriculture-related questions at https://extension.wisc.edu/agriculture/ask-an-agriculture-question/.

Disease - Herbaceous Ornamental, Disease - Vegetable

Edema

July 23, 2015 hudelson

UW Plant Disease Facts

Authors: Ann Joy and Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0048

What is edema?

Edema (or oedema) is a physiological disorder that frequently occurs in houseplants, greenhouse plants, and other plants sheltered under plastic. This disorder also affects field-grown vegetable crops under certain environmental conditions. Edema is often a cosmetic problem, but in extreme cases, edema can ruin a greenhouse crop and cause severe economic losses.

Edema pustules on the underside of a geranium leaf.

What does edema look like?

Small translucent, fluid-filled blisters form on the undersides of mostly older leaves, often beginning at the leaf margins. Blisters can also occur on stems and occasionally on flowers. When observed against the light, edema lesions are lighter in color than the surrounding leaf tissue. The blisters may increase in size or merge, burst, and then scar, turning tan in color and corky in texture. Some or all leaves may eventually shrivel or roll, and fall off. Extensive blistering and scarring may limit the plant’s ability to photosynthesize.

Where does edema come from?

When the soil is warm and moist, water absorbed by a plant’s roots may exceed the water lost through a plant’s leaves. Conditions preventing effective water loss include high relative humidity, low light intensity, cool air temperatures and poor ventilation. Periods of cloudy weather, or an increase in relative humidity resulting from cooling air temperatures, can make plants susceptible to edema. Edema has also been associated with the use of oil sprays that interfere with normal leaf water loss.

How do I save a plant with edema?

Edema is typically not fatal but will make plants less attractive. To limit problems with edema, water less frequently in cloudy periods or under low light intensity. Water in the morning so that the soil in which plants are potted will drain by nightfall when cooling temperatures can lead to increased relative humidity.

How do I avoid problems with edema in the future?

Use a growth medium that drains well. Reduce relative humidity near leaf surfaces by increasing plant spacing and air circulation. Increase light and air temperatures to help increase normal water loss. Water less frequently during cool, humid weather. Empty standing water in saucers under pots 30 minutes after watering.

For more information on edema:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

Thanks to Sr. Mary Francis Heimann, Kristin Kleeber ger and Ann Wied for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Vegetable

Early Blight

July 23, 2015 hudelson

UW Plant Disease Facts

Authors: Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0046

What is early blight?

Early blight is one of two common fungal diseases that can devastate tomatoes in both commercial settings and home gardens. Early blight can also be a serious disease on other popular vegetables including eggplants, peppers, and potatoes. The second common tomato blight, Septoria leaf spot, is detailed in UW Plant Disease Facts D100, Septoria Leaf Spot.

Early blight of tomato. Note spots with concentric rings (arrow) and yellow haloes.

What does early blight look like?

Symptoms of early blight first appear at the base of affected plants, where roughly circular, brown spots appear on leaves and stems. As these spots enlarge, concentric rings appear giving the areas a target-like appearance. Often spots have a yellow halo. Eventually multiple spots on a single leaf will merge, leading to extensive destruction of leaf tissue. Early blight can lead to total defoliation of lower leaves and even the death of an infected plant.

Where does early blight come from?

Early blight is caused by the fungus Alternaria solani, which survives on infected plants or in plant debris. Early blight symptoms typically begin as plant canopies start to close. Denser foliage leads to high humidity and longer periods of leaf wetness that favor the disease.

How do I save a plant with early blight?

Once symptoms of early blight appear, control is difficult. Thinning of whole plants or removal of selected branches from individual plants may slow the disease by increasing airflow and thus reducing humidity and the length of time that leaves remain wet. Fungicides labeled for use on vegetables and containing copper or chlorothalonil may also provide control of early blight if they are carefully applied very early in the course of the disease (before symptoms develop is best) and on a regular basis throughout the rest of the growing season. If you decide to use fungicides for disease control, be sure to read and follow all label instructions of the fungicide that you select to ensure that you use the product in the safest and most effective manner possible.

How do I avoid problems with early blight in the future?

Destroy infected plants and plant debris by burning (where allowed by local ordinance) or burying them. Move vegetables to different parts of your garden each year to avoid areas where the early blight fungus may be present. See University of Wisconsin Garden Facts XHT1210, Using Crop Rotation in the Home Vegetable Garden, for details on this technique. Use early blight-resistant vegetable varieties whenever possible. Increase spacing between plants to increase airflow, and decrease humidity and foliage drying time. Mulch your garden with approximately one inch of a high quality mulch, but DO NOT overmulch as this can lead to wet soils that can contribute to increased humidity. Finally, where the disease has been a chronic problem, use of preventative applications of a copper or chlorothalonil-containing fungicide labeled for use on vegetables may be warranted.

For more information on early blight:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

Thanks to Karen Delahaut, Lisa Johnson and Ann Joy for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Broad Leafed Woody Ornamental

Dutch Elm Disease

July 23, 2015 hudelson

UW Plant Disease Facts

Authors: Jim Olis* and Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0045

What is Dutch elm disease?

Dutch elm disease (DED) is a lethal fungal disease of native North American elms. The fungi that cause DED entered the United States early in the 1900’s on elm logs imported from Europe. DED now occurs throughout the United States and has led to the loss of the American elm as the premier street tree.

Dutch elm disease has led to the loss of the American elm as a street tree.

What is Dutch elm disease?

Where does Dutch elm disease come from?

DED is caused by two fungi, Ophiostoma ulmi and Ophiostoma novo-ulmi. These fungi are thought to have originated in Asia and were spread as elm trees and wood were moved from location to location. Once these fungi are introduced into an area, they are moved to healthy trees by two species of elm bark beetles (one native, one of European origin). These beetles breed in stressed trees (which include those trees suffering from DED), then carry spores of the DED fungi to healthy trees and inoculate the trees as they feed. Once DED fungi gain entry into an elm, they can move to other nearby elms underground via root grafts. Human activities such as pruning can lead to spread of these fungi as well.

How do I save a tree with Dutch elm disease?

Elms suffering from DED should be removed. Prior to removal, disrupt root grafts between the infected elm and other nearby healthy elms using a mechanical trencher or vibratory plow. If you do not disrupt root grafts, removal of the infected tree may accelerate movement of DED fungi through root grafts to adjacent trees. Destroy wood from diseased elms by burning (where allowed by local ordinance) or burying it. If you decide to keep the wood, remove the bark, then pile the wood and cover it with a heavy tarp, burying the tarp edges with soil, until the wood is used. Covering the wood limits access by elm bark beetles that potentially could pick up DED fungi from the cut wood and move them to other trees.

Discoloration of wood just under the bark of elm branches can indicate the presence of one of the DED fungi.

If you decide not to remove an infected elm, at least remove, then bury or burn, dead or dying branches. Make cuts six feet below any area showing symptoms. Disinfect cutting tools between each cut by treating them for at least 30 seconds with a 10% bleach solution or (preferably due to its less corrosive properties) 70% alcohol (e.g., rubbing alcohol or certain spray disinfectants). If you use bleach, be sure to thoroughly rinse and oil your tools after pruning to prevent rusting.

How do I avoid problems with Dutch elm disease in the future?

Fungicide injections of either propiconazole or thiabendazole can be useful for protecting high value, healthy American elm trees. Such injections are of limited use if trees are already infected. For best results, trees should be treated every two years by a certified arborist with additional training in making injection treatments.

If you decide to plant an elm, use non-native hybrid elms, such as “Accolade”, “New Horizon”, “Regal” and “Frontier”, that are resistant to DED. DED resistant American elm varieties are also currently available. Look for varieties such as “American Liberty”, “Independence”, “Princeton”, “New Harmony” and “Valley Forge” at your local nursery or garden center. Keep in mind however that resistance is not immunity, and even DED-resistant elm varieties can become infected. Typically however, in resistant varieties, DED does not develop as rapidly, providing time and opportunity to attempt to manage the disease using other strategies (e.g., pruning, fungicide injections).

For more information on Dutch elm disease:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

*Completed as partial fulfillment of the requirements for a BS in Plant Pathology at the University of Wisconsin Madison

Thanks to Lis Friemoth, Ann Joy and Laura Jull for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Broad Leafed Woody Ornamental, Disease - Field and Forage, Disease - Fruit Crop, Disease - Herbaceous Ornamental, Disease - Specialty Crop, Disease - Vegetable

Downy Mildew

July 21, 2015 hudelson

UW Plant Disease Facts

Authors: Jim Olis* and Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0044

What is downy mildew?

The downy mildews are a group of diseases that cause destruction of the leaves, stems, flowers and fruits of many plant species worldwide. In Wisconsin, downy mildews have traditionally been problems on grapes, cucumbers (see UW Bulletin A3978, Cucurbit Downy Mildew: Identification and Management, available at https://learningstore.extension.wisc.edu/), roses and Viburnum. Downy mildews on basil (see UW Plant Disease Facts D15, Basil Downy Mildew) and impatiens (see UW Plant Disease Facts D66, Impatiens Downy Mildew) have more recently become problematic.

What does downy mildew look like?

Downy mildew symptoms begin as small, green or yellow, translucent spots that can eventually spread to an entire leaf, stem, flower or fruit. Infected plant parts may eventually brown or bronze. The causal organism appears on infected stems, flowers and fruits, and on undersurfaces of infected leaves, as a downy, white, gray or purple fuzz.

Where does downy mildew come from?

Downy mildew is caused by several closely related fungus-like water molds (e.g., Peronospora spp., Plasmopara spp. and Pseudoperonospora spp.) that survive in plant debris or on infected plants. Downy mildew organisms are fairly host specific. The downy mildew organism that infects one type of plant (e.g., rose) is not the same downy mildew organism that infects another (e.g., grape). However, if you see downy mildew on one plant, then environmental conditions (i.e., cool, wet weather) are favorable for development of downy mildews on a wide range of plants.

How do I save a plant with downy mildew?

Downy mildews can be controlled using fungicides, if treatments are applied early enough in disease development. Fungicides containing chlorothalonil and copper (particularly Bordeaux mix, a combination of copper sulfate and lime) are labeled for downy mildew control in home gardens. Timing and number of applications will vary depending on exactly the type of downy mildew you are attempting to control. Be sure to read and follow all label instructions of the fungicide that you select to ensure that you use the product in the safest and most effective manner possible.

How do I avoid problems with downy mildew in the future?

Consider buying downy mildew resistant varieties, when available. In new plantings, space plants far apart. In established plantings, prune or thin plants to increase airflow. Proper spacing and thinning will reduce humidity and promote rapid drying of foliage, which is less favorable for downy mildew development. Avoid overhead watering and apply water directly to the soil at the base of your plants. At the end of the growing season, remove and destroy infected plant debris as this can serve as a source of spores for the next growing season.

For more information on downy mildew:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

*Completed as partial fulfillment of the requirements for a BS in Plant Pathology at the University of Wisconsin Madison.

Thanks to Lisa Johnson, Ann Joy and Kristin Kleeberger for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Needled Woody Ornamental

Dothistroma Needle Blight

July 21, 2015 hudelson

UW Plant Disease Facts

Authors: Jim Olis* and Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0043

What is Dothistroma needle blight?

Dothistroma needle blight is a common needle disease that can affect over thirty species of pine trees. In Wisconsin, Austrian pines are most commonly and severely affected by this disease.

Brown needle tips are a typical symptom of Dothistroma needle blight.

What does Dothistroma needle blight look like?

Dothistroma needle blight first appears as dark green, water-soaked spots on the needles. The spots become tan, yellow, or reddish-brown, and may encircle the needles to form bands. The tip of the needle beyond the band eventually dies, leaving the base of the needle alive and green. Young trees are more likely to suffer damage than older trees. Seedlings (< 1 yr. old) can be killed within a year after infection.

Where does Dothistroma needle blight come from?

Dothistroma needle blight is caused by the fungus Dothistroma pini, which survives in diseased needles. Watch for tiny, black reproductive structures of the fungus (called pycnidia) that can be found erupting from the surface of infected needles. Spores are produced in these structures throughout the growing season, and infection by spores can occur at any time, but particularly during periods of wet weather. Symptoms appear from five weeks to six months after infection.

How do I save a tree with Dothistroma needle blight?

Copper-containing fungicides (e.g., Bordeaux mix) can help prevent new infections, but will not cure diseased needles. Typically a single fungicide application in early June is sufficient to provide protection of new foliage. However, a second application three to four weeks later will provide more complete control. Be sure to read and follow all label instructions of the fungicide that you select to ensure that you use the product in the safest and most effective manner possible. Several years of treatments may be needed to completely rid a tree of all infected needles (through natural needle loss).

How do I avoid problems with Dothistroma needle blight in the future?

DO NOT plant Austrian pines as they are extremely susceptible to Dothistroma needle blight. Consider using other conifers instead. If you decide to plant susceptible trees, make sure the trees are disease-free at the time of planting. Also, be sure to provide adequate spacing between the trees to ensure good airflow and promote rapid needle drying. If you have established trees that are suffering from Dothistroma needle blight, remove fallen needles from around the base of these trees as these can serve as a source of fungal spores.

For more information on Dothistroma needle blight:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

*Completed as partial fulfillment of the requirements for a BS in Plant Pathology at the University of Wisconsin Madison.

Thanks to Ann Joy, Laura Jull and Patti Nagai for r eviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Broad Leafed Woody Ornamental, Disease - Field and Forage, Disease - Fruit Crop, Disease - Herbaceous Ornamental, Disease - Needled Woody Ornamental, Disease - Vegetable, Misc, Turf

Dodder

July 21, 2015 hudelson

UW Plant Disease Facts

Authors: Jennifer Clifford, Amilcar Sanchez, Trenton Stanger, and Brian Hudelson UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0129

Spaghetti-like dodder plants parasitizing carrots.

What is dodder?

Dodder is the name of several species of parasitic plants that are widely distributed in North America and Europe. Plants parasitized by dodder include alfalfa, carrots, onions, potatoes, cranberries, a variety of herbaceous and woody ornamentals, and many weed species. Parasitized plants become weakened, have reduced yields (in the case of agronomic crops), and can potentially die.

What does dodder look like?

Dodders lack roots and leaves, and also lack chlorophyll, the green pigment found in most plants. Dodders have slender, yellow-orange stems that cover infected plants in a spreading, tangled, spaghetti-like mass. From May through July, dodders produce white, pink, or yellowish flowers.

Where does dodder come from?

Dodders produce large numbers of seeds that germinate in the spring to produce shoots that attach to suitable host plants. Dodders penetrate host tissue, and absorb nutrients via specialized structures called haustoria. Once established on a host, the bottom of a dodder plant dies (thereby severing its connection with the soil), and the dodder plant becomes dependent on the host plant for water and nutrients.

How do I save plants parasitized by dodder?

On woody ornamentals, simply prune out dodder-parasitized branches. When small patches of dodder occur among herbaceous plants, apply contact herbicides such as 2,4-D early in the season, preferably before dodder seedlings have parasitized host plants. Keep in mind that use of contact herbicides will likely also kill host plants. Alternatively, cut or burn dodder and parasitized plants to keep dodder from spreading, and to prevent seed production. For widespread dodder infestations, a combination of frequent tilling, burning and herbicide applications may be needed to achieve control. Be sure to read and follow all label instructions of the herbicide that you select to ensure that you use the product in the safest and most effective manner possible.

How do I avoid problems with dodder in the future?

Dodder’s wide host range and ability to survive as dormant seeds in soil make eradication difficult. Preventing introduction of dodder is the best method of control. Use dodder-free seed, and be sure to clean equipment thoroughly after working in a dodder-infested area. Try to restrict animal movement between infested and non-infested areas as well. Depending upon the specific crop or location, use of pre-emergent herbicides containing DCPA, dichlobenil, propyzamide, or trifluralin may be possible to prevent germination of dodder seeds. Destroy actively growing dodder and any parasitized plants before the dodder produces seeds. In agricultural settings where dodder has been a problem, rotate away from susceptible crops and grow non-host crops (e.g., corn, soybeans, or small grain cereals). In conjunction with rotation, adequate control of weed hosts is critical to achieve control.

For more information on dodder:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

Thanks to Lis Friemoth, Matt Lippert and Dan O’Neil for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Broad Leafed Woody Ornamental, Disease - Fruit Crop, Misc

Dead Man’s Fingers

July 19, 2015 hudelson

UW Plant Disease Facts

Authors: Ann Joy and Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0040

What is dead man’s fingers?

Dead man’s fingers are mushroom-like fungal growths that can be found at the base of dead or dying trees and shrubs, as well as at the base of wood objects (e.g., wood barrels) that are in contact with soil. Some types of dead man’s fingers are produced by wood-decomposing fungi. Others are produced by fungi that cause black root rot. This disease typically is a problem on stressed trees or shrubs, including apple, crabapple, pear, cherry, plum, American elm, Norway maple and honeylocust.

Dead man’s fingers growing from mulch next to a barrel planter. (Photo courtesy of Dick Becker)

What does dead man’s fingers look like?

The most recognizable dead man’s fingers are those that are black and club-shaped with a white interior, appearing as solitary or clustered irregularly-shaped “fingers” that are approximately 1½ to 4 inches tall. They form on or near dead or dying wood. In the spring, as the “fingers” first form, they may be pale blue with white tips. Disease-causing species of the fungus initially form a pale sheath around roots that later becomes black and crusty, hiding a lighter interior. This sheath/crust is sometimes visible when soil is brushed away from tree/shrub roots. Trees/shrubs with above-ground symptoms of infection may show decline, dieback, slowed growth, and basal cankers. Infected apple trees may produce an abnormally large crop of smaller than normal-sized fruits.

Where does dead man’s fingers come from?

Dead man’s fingers are sexual reproductive structures of fungi in the genus Xylaria. Sexual spores (called ascospores) are produced inside each club-like “finger” and released through a tiny hole in the top. The “fingers” can release these spores for several months or years. In the spring, Xylaria can produce asexual spores (called conidia) anywhere on its surface. Xylaria also produces threadlike structures (called hyphae) that grow through dead or dying wood. Xylaria can survive as hyphae in roots for up to 10 years, and can spread from plant to plant via hyphae when plant roots come in contact with each other.

How can I save a tree with dead man’s fingers?

In urban settings, dead man’s fingers may grow from wood mulch and may not be an indication of disease. Simply remove and discard the “fingers” if you find them unsightly. If dead man’s fingers form around or near the base of an apple, crabapple or other known susceptible host, the fungus may be infecting the tree, causing black root rot. In this situation, by the time the characteristic “fingers” appear, the infection is well advanced. An infected tree should be carefully removed, including the stump and as much of the root system as possible. DO NOT use wood from Xylaria-infected trees for mulch. There are no fungicides registered in Wisconsin for treatment of black root rot.

How can I prevent dead man’s fingers from being a problem in the future?

DO NOT plant susceptible trees or shrubs in a site where dead man’s fingers has been observed. In addition, make sure that susceptible trees/shrubs in other locations are well watered, fertilized, mulched and otherwise maintained to reduce stresses that might predispose them to infection by disease-causing species of Xylaria. Unfortunately, Xylaria-resistant tree and shrub varieties/cultivars are not available.

For more information on dead man’s fingers:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

Thanks to Jane Anklam, Mark Kopecky and Judy Reith – Rozelle for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.