Category Archives: Disease – Needled Woody Ornamental

Phytophthora Root Rot of Christmas Trees

Phytophthora root rot can cause severe losses in commercial Christmas tree production. (Photo courtesy of Sara Ott)
Phytophthora root rot can cause severe losses in commercial Christmas tree production. (Photo courtesy of Sara Ott)

What is Phytophthora root rot?  Phytophthora root rot is a common disease of Christmas trees including Douglas-fir, true firs (e.g., Fraser, balsam and Canaan), spruces, and pines.  The disease has caused significant problems in Christmas tree production in several states.  In Wisconsin, losses due to Phytophthora root rot have been particularly high in Fraser fir Christmas tree production.

What does Phytophthora root rot look like?  Symptoms of Phytophthora root rot are often not observed until the disease is quite advanced.  Above ground, affected trees initially have single branches (typically low on the tree) with needles that turn from green to yellow to red-brown, and remain on the tree.  Soft, sunken areas (i.e., cankers) may also form on trunks near the soil line.  As the disease progresses, trees wilt and die.  Below ground, affected trees have root systems with a reduced number of fine, water-absorbing roots.  What roots remain are often black and lack white growing points.  The outer tissue of these roots easily sloughs off and the interior root tissue is also typically discolored.  Discolored roots may, but oftentimes do not, have a foul odor.

Where does Phytophthora root rot come from?  Phytophthora root rot is caused by several species of the water mold (i.e., fungus-like organism) Phytophthora.  WI DATCP staff have recently identified six Phytophthora species (P. cactorum, P. europaea, P. megasperma, P. plurivora, P. sansomeana, and P. sp. ‘kelmania’) that can be involved in Christmas tree root rot in Wisconsin.  These organisms can survive for many years in soil and plant debris as thick-walled resting spores (called oospores) that can eventually germinate and directly infect trees.  Alternatively during wet periods, certain of these oospores can germinate to produce swimming spores that are attracted to the roots of Christmas trees and other host plants.  Oospores can be moved from field to field on seedlings and transplants, on soil clinging to field equipment and hand tools, in irrigation or flood water, and even on boots and shoes.

Extensive external and internal darkening of root tissue is typical of Phytophthora root rot.
Extensive external and internal darkening of root tissue is typical of Phytophthora root rot.

How do I save a plant with Phytophthora root rot?  If you have trees that you suspect are suffering from Phytophthora root rot, have them examined by a professional plant disease diagnostician.  If the diagnostician confirms Phytophthora root rot, dig up and burn any symptomatic trees and limit access to the area of the field where the trees were grown.  Quarantining the area can help limit spread of contaminated soil to other areas of the field.  Fungicide treatments will NOT cure trees suffering from Phytophthora root rot.  However, fungicide treatments in the last year of production may be useful in limiting development of visible root rot symptoms on trees growing near a Phytophthora-infested area so that these trees can be successfully marketed.  Fungicides containing mono- and di- potassium salts of phosphorous acid, metalaxyl (mefenoxam) and etridiazole are registered for Phytophthora management in Christmas tree production in Wisconsin.  DO NOT use the same active ingredient for all treatments.  Alternate the use of at least two active ingredients with different modes of action to help minimize problems with fungicide-resistant strains of Phytophthora.  Be sure to read and follow all label instructions of the fungicides that you select to ensure that you use them in the safest and most effective manner possible.

How do I avoid problems with Phytophthora root rot in the future?  Choose sites with well-drained soils and avoid planting in low areas where water drains and pools.  DO NOT plant Christmas trees in sites that may have had a history of Phytophthora root rot including nurseries, orchards and soybean fields.  Phytophthora species that cause problems on shrubs, trees and even soybeans can also cause problems on Christmas trees.  Buy healthy Christmas tree seedlings from a reputable grower.  Carefully plant seedlings making sure that planting holes are large enough for roots to spread in all directions.  This will reduce the likelihood of girdling or J-roots that may make trees more prone to infection.  Also, minimize root wounding at planting, and avoid soil compaction by heavy equipment.  Water trees adequately, but DO NOT overwater.  Use well water for irrigation, if possible.  Avoid using water from ponds, rivers and streams as this water may be contaminated with Phytophthora.  Routinely inspect Christmas tree plantings for symptoms of Phytophthora root rot and follow the recommendations outlined above if you notice symptoms of the disease.

For more information on Phytophthora root rot of Christmas trees:  Contact your county Extension agent.

Phomopsis Tip Blight

What is Phomopsis tip blight?  Phomopsis tip blight is one of the most common fungal diseases of conifers in Wisconsin.  It is most severely affects junipers (e.g., Eastern red cedar, creeping and Rocky Mountain junipers) but can also cause issues on arborvitae, Douglas-fir, true firs, larch, pines and spruces.

Die-back of juniper branch tips caused by Phomopsis tip blight.
Die-back of juniper branch tips caused by Phomopsis tip blight.

What does Phomopsis tip blight look like?  On junipers, small gray lesion (spots) first form on the terminal four to six inches of new shoots in early spring.  Infected branches typically initially turn dull red or brown, and then ash-gray as lesions girdle and kill branch tips.  Small, black pycnidia (the reproductive structures of the causal fungus) can easily be seen on dead branches with the unaided eye or with a hand lens.  Severe infections may result in death of an entire juniper.  Phomopsis tip blight rarely kills other conifer hosts, although branch dieback is a typical symptom.

Where does Phomopsis tip blight come from?  Phomopsis tip blight is caused by several fungi currently or formerly classified in the genus Phomopsis.  These fungi survive in diseased and dead branches.  Spores of these fungi are produced throughout the growing season, and are spread by wind and rain.  Infections can occur whenever new foliage is produced, and moisture or humidity is high.  Most infections occur in the spring, but late summer infections can occur if over-watering or over-fertilization stimulates new growth.

How do I save a juniper with Phomopsis tip blight?  Prune out and destroy diseased branches as they appear.  Always prune in dry weather, and cut four to six inches below obviously diseased areas on each branch.  Decontaminate pruning tools after 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).  For particularly susceptible junipers, combine pruning with use of copper or mancozeb-containing fungicides.  Make applications at seven to 21 day intervals during rapid growth in the spring.  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 Phomopsis tip blight in the future?  Plant only resistant juniper species, varieties, and cultivars.  DO NOT plant conifers in poorly drained sites or heavily shaded areas.  DO NOT overcrowd trees and shrubs in new plantings.  Provide adequate space between plants to promote good air circulation and rapid drying of foliage.  DO NOT prune or shear conifers excessively as this stimulates excessive new, susceptible growth.  If possible, DO NOT use overhead sprinklers for watering.  Use a soaker or drip hose instead.  If you must overhead water, water early in the day to allow for fast drying of plants.

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

Nectria Canker

What is Nectria canker?  Nectria canker is a common and potentially lethal disease that affects many species of trees and shrubs.  This disease can cause significant damage on newly planted, as well as established, trees and shrubs that are under stress.

Nectria canker on a honey locust tree. The site of infection was a pruning wound.
Nectria canker on a honey locust tree. The site of infection was a pruning wound.

What does Nectria canker look like?  Nectria canker is characterized by the formation of sunken areas (cankers) that form on twigs, branches, and trunks.  Cankers can form at leaf scars and wherever injuries occur.  Injuries can be caused by pruning (particularly improper pruning), frost, hail, cracking from heavy snow or ice, sunscald, insects, or animals.  Cankers appear first as slightly sunken areas on the bark, but can grow for years, becoming target-shaped or elongated.  Small branches girdled by cankers can wilt suddenly, fail to leaf out, and die.

Where does Nectria canker come from?  Nectria canker is caused by two fungi, Nectria cinnabarina and Nectria galligena.  These fungi survive in the margins of cankers where they produce numerous fruiting bodies (reproductive structures).  Fruiting bodies can be cream, coral, orange, or red, and eventually darken to brown or black with age.  Spores are dispersed by wind, water, and pruning tools.  Cankers expand slowly, usually when the host is dormant or under stress.  Infected plants may hold the fungus in check by producing wound-closing (callus) tissue around the infected area.

How do I save a tree with Nectria canker?  There is no cure for Nectria canker.  Remove smaller branch cankers by pruning six to eight inches below the canker.  Disinfect pruning tools after each cut by treating them for at least 30 seconds with 10% bleach solution or (preferably due to its less corrosive properties) 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.  Trees with trunk cankers may live many years with the disease.  Healthy trees are better able to slow the development of Nectria canker, so make sure that trees are watered and fertilized properly.

How do I avoid problems with Nectria canker in the future?  Choose plants that are well-adapted to your local climate.  Avoid any stresses to your trees and shrubs.  Prune trees and shrubs properly.  See UW-Garden Facts XHT1014, Pruning Deciduous Trees, and XHT1015, Pruning Deciduous Shrubs), and avoid injury to root and trunks from lawnmowers.  Remove grass from around the base of trees and shrubs, mulch properly, and water as needed to avoid drought stress.

For more information on Nectria canker:  See UW Bulletin A3281, Honey Locust Disorder:  Canker Diseases in Wisconsin (available at https://learningstore.extension.wisc.edu/), or contact your county Extension agent.

Herbicide Damage

What is herbicide damage?  Herbicide damage is any adverse, undesired effect on a plant that is caused by exposure of that plant to a pesticide designed for weed control (i.e., an herbicide).  Any plant can be subject to this problem.

Squash leaf distorted due to exposure to a common lawn herbicide.
Squash leaf distorted due to exposure to a common lawn herbicide.

What does herbicide damage look like?  Symptoms of herbicide damage vary depending upon the plant affected and the herbicide used.  Common symptoms include stems that are flattened, or that twist or corkscrew.  Leaves may have abnormal shapes, sizes or textures.  In addition, leaves or leaf veins may yellow or redden.  In severe cases, plants may brown and die.  Some plants, such as tomatoes and grapes, are particularly susceptible to herbicide damage and can be used as indicators of unwanted herbicide exposure.

How does herbicide damage occur?  Herbicide damage results when an herbicide is misapplied.  Herbicides for control of broadleaf weeds are occasionally applied with fertilizers as part of a lawn care program.  If these products are applied too close to ornamentals or vegetables, or are applied when there is too much wind, then the herbicide can drift (move) from the area of application into a non-treated area.  Often, drifting herbicides are difficult to detect by eye because they are extremely fine mists.  They can better be detected by smell.  Some herbicides readily produce vapors that can begin to drift several hours after application.

How do I save a plant that has been damaged by herbicides?  There is nothing you can do after plants have been exposed.  However, most plants accidentally exposed to broadleaf herbicides applied with lawn fertilizers do not receive a high enough dose to kill them.  Young growth exposed to the herbicide will be distorted and discolored, but subsequent growth will be normal.

How do I avoid problems with herbicide damage in the future?  When using a lawn herbicide, follow the application directions exactly.  DO NOT apply the product too close to, or in a manner that will cause exposure to, non-target ornamentals or vegetables.  To avoid drift, apply the herbicide when there is as little wind as possible (< 5 mph).  Apply the herbicide at low pressure to minimize production of fine mists.  Finally, use amine forms rather than ester forms of herbicides as amine forms are less likely to produce vapors.

For more information on herbicide damage:  See UW Bulletin A3286, Plant Injury Due to Turfgrass Broadleaf Weed Herbicides (available at https://learningstore.extension.wisc.edu/), or contact your county Extension agent.

Dothistroma Needle Blight

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.
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:  See UW Bulletin A2620, Pine Disorder:  Dothistroma Needle Blight (available at https://learningstore.extension.wisc.edu/), or contact your county Extension agent.

Cytospora Canker

What is Cytospora canker?  Cytospora canker is one of the most common fungal diseases of Colorado blue spruce.  This disease can also affect Engelmann, Norway and white spruce, as well as balsam fir, Douglas-fir, European larch, tamarack, and white pine.  Trees that are 15 years old or older and are at least 20 feet high often show symptoms of Cytospora canker.  Cytospora canker can kill trees, but more often simply makes trees so unsightly that owners opt to remove the trees.

Death of lower branches of Colorado blue spruce typical of Cytospora canker.
Death of lower branches of Colorado blue spruce typical of Cytospora canker.

What does Cytospora canker look like?  Cytospora canker usually first appears on lower branches and progresses up the tree, although individual upper branches may show symptoms as well.  Needles on infected branches turn purple, then brown.  Diseased needles eventually fall off, and infected branches die.  Infected branches often ooze a bluish-white sap somewhere along their length.

Where does Cytospora canker come from?  Cytospora canker is caused by the fungus Cytospora kunzei (also sometimes referred to as Leucocytospora kunzei or Leucostoma kunzei).  The fungus survives in infected branches and spores are spread by wind, rain splash, insects, birds, and mammals.

How do I save a tree with Cytospora canker?  Immediately remove and destroy any diseased branches by pruning them using the three-point method of pruning (see University of Wisconsin Garden Facts XHT1014, How to Properly Prune Deciduous Trees, for details).  Prune only in dry weather.  Between cuts, decontaminate pruning tools by treating them for at least 30 seconds in 10% bleach or (preferably due to its less corrosive properties) 70% alcohol (e.g., rubbing alcohol, certain spray disinfectants).  Decontaminating tools will help prevent movement of Cytospora kunzei from branch to branch and from tree to tree during pruning.  If you use bleach, be sure to thoroughly rinse and oil tools after pruning to prevent rusting.

Bluish-white ooze often is present on branches affected by Cytospora canker.

How do I avoid problems with Cytospora canker in the future?  Perhaps the easiest way to avoid Cytospora canker is through proper tree selection, planting and maintenance.  Avoid planting full-sized varieties of trees susceptible to Cytospora canker, particularly full-sized varieties of blue spruce.  Instead plant dwarf tree varieties.  Smaller trees will have canopies where air will more easily penetrate into the interior, thus drying branches and needles more rapidly.  In general, a drier environment is less favorable for disease development.  If you choose to plant a full-sized tree, leave adequate space between the tree and other trees in your landscape.  Proper spacing will provide good air flow and again promote drier conditions that are less favorable for disease.  Optimally, when trees are full sized, they should be far enough apart so that branches do not overlap.  As a tree becomes well established, selectively prune branches to open up the tree’s canopy to further promote a drier environment.

Also minimize environmental stresses to any tree susceptible to Cytospora canker.  Prevent water stress by avoiding soil compaction and by ensuring adequate soil drainage.  During dry periods, make sure your tree receives approximately one inch of water per week either from natural rain or by applying supplemental water at the drip line of the tree (i.e., the edge of where tree branches extend) and beyond using a soaker or drip hose.  To help maintain proper soil moisture, mulch out to at least the drip line of the tree.  Use one to two inches of mulch on a heavier, clay soil; use three to four inches of mulch on a lighter, sandy soil.  DO NOT pile mulch against the trunk of the tree; keep mulch approximately four inches from the trunk.  Prevent nutrient stress by properly fertilizing your tree based on a soil fertility test provided by an accredited lab.

DO NOT use fungicide treatments for Cytospora canker control; fungicide treatments are not effective.

For more information on Cytospora canker:  See UW Bulletin A2639, Colorado Blue Spruce and Other Spruce Disorder:  Cytospora Canker (available at https://learningstore.extension.wisc.edu/), or contact your county Extension agent.

Chlorosis

What is chlorosis?  Chlorosis is a common nutritional disorder of many woody ornamentals in Wisconsin, particularly in the southern and eastern parts of the state.  Pin oaks are most commonly affected by chlorosis, although many other trees and shrubs (e.g., white oaks, red maples, white pines and rhododendrons) are also very susceptible.

Yellowing of foliage characteristic of chlorosis.
Yellowing of foliage characteristic of chlorosis.

What does chlorosis look like?  Symptoms of chlorosis are easy to distinguish from those of other diseases.  Affected leaves turn yellow, except for the veins, which remain green.  In severe cases, foliage may turn brown and die.  Symptoms can occur on isolated branches, or over an entire tree.

What causes chlorosis?  Chlorosis occurs when a tree or shrub is lacking certain micronutrients, in many cases iron or manganese.  Lack of micronutrients in a tree may reflect a lack of these nutrients in the soil due to poor fertility.  Often however, there are sufficient micronutrients, but they cannot be absorbed by a plant’s roots.  Poor absorption of micronutrients is common in Wisconsin because of the high pH (alkalinity) of many soils.

How do I save a tree or shrub with chlorosis?  Chlorosis is rarely fatal and can be treated.  For treatments to be effective, you must determine the exact cause of the chlorosis.  Have the soil around an affected plant tested for micronutrients and for pH prior to applying any treatment.  If the soil test indicates a lack of specific micronutrients, fertilize with these micronutrients.  For example, chelated iron compounds can be used to increase the amount of iron in soil.  If the soil test indicates a high soil pH, lower the pH by applying sulfur or ammonium sulfate.  See University of Wisconsin Garden Facts XHT1151, Reducing Soil pH, for details.  Contact your county Extension agent for information on soil testing and for tips on a treatment once you have determined the specific cause of your chlorosis problem.

How do I avoid problems with chlorosis in the future?  Plant trees and shrubs that are less susceptible to chlorosis.  Also, make sure your trees and shrubs receive sufficient water (approximately one inch per week), as this will help plants with micronutrient uptake.  During dry periods, use a drip hose or soaker hose to apply supplemental water.  Remove turf from around the bases of trees and shrubs out to at least the drip lines, and apply shredded hardwood, pine or cedar mulch in these areas to help maintain soil moisture.  On heavy clay soils, use one to two inches of mulch.  On other soils, use three to four inches of mulch.  Be sure to keep mulch four inches from the trunks of trees.  If you decide to plant susceptible trees or shrubs, watch them closely for the yellowing characteristic of chlorosis, and apply corrective treatments as soon as symptoms appear.  Treatments should always be based on the results of soil micronutrient and pH tests.

For more information on chlorosis:  Contact your county Extension agent.

Armillaria Root Disease

What is Armillaria root disease?  Armillaria root disease, also known as shoestring root rot, is an often lethal disease of tree and shrubs.  It can affect almost any conifer or hardwood species, from seedling to maturity.  Herbaceous plants can also be affected.  Trees and shrubs stressed due to drought or defoliation can be particularly susceptible to Armillaria root disease.

Armillaria Root Disease
White mats of fungal tissue called mycelial fans (arrow) may be present within and beneath the bark of stems and roots affected by Armillaria root disease.

Where does Armillaria root disease come from?  Armillaria root disease results from colonization of trees and shrubs by fungi in the genus Armillaria.  These fungi produce tough, cord-like strands called “rhizomorphs” that grow from decaying stumps and roots through the soil.  Infection of other trees or shrubs can result from penetration of intact roots by rhizomorphs.  In late summer or early fall, honey-colored mushrooms of Armillaria fungi develop near the bases of colonized plants and produce spores that are distributed by wind.  Infection also can occur after these spores germinate in wounds on stems or roots.

What does Armillaria root disease look like?  Above-ground symptoms of Armillaria root disease may include slow growth, yellowing and dwarfing of foliage, and thin crowns.  Dieback of twigs and branches also may occur as the disease progresses.  These symptoms may develop slowly and intensify over many years.  However, trees and shrubs also may be rapidly killed, with leaves or needles suddenly wilting or browning on a plant that appeared healthy just days or weeks earlier.  Bark on lower stems or roots may be killed and crack, with flow of resin common on conifers.  Thin white mats of fungal tissue called “mycelial fans” may be present within and beneath killed bark.  Stem and root tissue decayed by Armillaria fungi is often water-soaked, creamy to yellow in color, and spongy or stringy in texture.  Rhizomorphs are commonly seen on or beneath the bark and growing from decayed stumps and roots.

How do I save a tree affected by Armillaria root disease?  There is no practical way to eliminate Armillaria from trees that are already colonized by the fungus.  The useful life of an affected tree might be prolonged however, by supplemental watering during dry periods and appropriate fertilization to improve overall host condition.  In very vigorous trees, the Armillaria fungi may be “walled off” and confined to just a portion of the root system or root collar.  There are no chemical treatments that can effectively target Armillaria fungi within diseased trees.

How do I avoid Armillaria root disease in the future?  Practices that maintain trees in vigorous condition are the best means of preventing Armillaria root disease.  Watering and fertilization to avoid stress will help trees resist infection.  Because Armillaria root disease often develops in response to defoliation, suppression of both insect and leaf pathogen defoliators will indirectly reduce the occurrence and severity of Armillaria root disease.  Because stumps and root systems of previously colonized trees can serve as “food bases” supporting rhizomorph growth for many years, thorough removal of stumps and root systems will reduce the risk of infection of other trees.

For more information on Armillaria root disease:  Contact your county Extension agent.