Category Archives: Disease – Needled Woody Ornamental

Gymnosporangium Rusts

January 24, 2019 ddlang

UW Plant Disease Facts

Authors: Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 03/01/2024

D-number: D0058

What are Gymnosporangium rusts?

Gymnosporangium rusts are a group of closely related diseases caused by fungi that infect both junipers (in particular red cedar) and woody plants in the rose family such as, but not limited to, apple, crabapple, hawthorn and quince. These fungi must infect both types of plants to complete their life cycles. The most common Gymnosporangium rusts found in Wisconsin are cedar-apple rust, cedar-hawthorn rust and cedar-quince rust. The names of these diseases are somewhat misleading, given that all three diseases can affect multiple rosaceous hosts in addition to those referenced in their names.

Yellow cedar-apple rust spots on an apple leaf (left) and slimy, orange, gelatinous cedar-apple rust galls on a juniper branch (right).

What do Gymnosporangium rusts look like?

On junipers, symptoms of Gymnosporagium rusts vary. Cedar-hawthorn and cedar-apple rust fungi induce formation of irregularly-shaped brown galls, with cedar-hawthorn rust galls tending to be smaller in size (approximately ¹/₈ to ⁹/₁₆ inch in diameter) than cedar-apple rust galls (approximately ¹/₄ to 2 inches in diameter). Both types of galls produce distinctive slimy, orange, gelatinous appendages in the spring. In contrast, the cedar-quince rust fungus causes juniper branch swellings. Orange spores ooze from these swollen areas in the spring.

On rosaceous hosts, Gymnosporangium rust symptoms also vary. Symptoms of cedar-hawthorn rust and cedar-apple rust appear in mid to late May, typically as circular, yellow-orange areas on leaves. Eventually, tube-like structures (that have a fringe-like appearance) form on the undersides of leaves beneath the yellow spots. Symptoms of cedar-quince rust typically become obvious later in the summer (most commonly on hawthorns) as swollen, spiny branches and/or fruits.

Where do Gymnosporangium rusts come from?

Several fungi in the genus Gymnosporangium cause Gymnosporangium rusts. These include Gymnosporangium juniperi-virginianae (cedar-apple rust), Gymnosporangium globosum (cedar-hawthorn rust), and Gymnosporangium clavipes (cedar-quince rust). These fungi overwinter in infected branches and galls on junipers. Spores oozed from the infected branches or produced in the gelatinous gall appendages drift to rosaceous hosts leading to leaf and fruit infections. Similarly, spores produced in the tube-like structures/spines on rosaceous leaves and fruits drift to junipers leading to new branch infections and additional gall formation.

How do I save a tree or shrub with Gymnosporangium rust?

Gymnosporangium rusts are primarily cosmetic diseases that make susceptible plants unattractive, but rarely have long-term detrimental effects. Gymnosporangium rusts on leaves can, for all practical purposes, be ignored. Gymnosporangium rusts on juniper branches can be easily managed by pruning approximately four to six inches below swollen areas or galls. Rosaceous hosts with infected branches can be pruned similarly. Be sure to decontaminate pruning tools between cuts by treating them for at least 30 seconds in 70% alcohol (e.g., rubbing alcohol or certain spray disinfectants) or 10% bleach. Decontaminating tools will prevent movement of rust fungi from branch to branch or from plant to plant during pruning. If you use bleach, be sure to thoroughly rinse and oil your tools after pruning to prevent rusting.

How do I avoid problems with Gymnosporangium rusts in the future?

The best way to avoid Gymnosporangium rusts is to not grow junipers (particularly red cedar) and susceptible rosaceous hosts close to one another. In urban settings where yards are small however, keeping both hosts adequately separated may be impossible. Where Gymnosporangium rusts have consistently been a problem, consider using evergreens (e.g., pine, fir, spruce) and flowering trees and shrubs (e.g., cherry, plum, lilac) that are immune to these diseases. If you decide that you want to mix junipers with apple, crabapple, hawthorn, and quince on your property, check at your local nursery for resistant varieties that will satisfy your landscaping needs. In general, Chinese junipers (Juniperus chinensis) tend to be relatively resistant to Gymnosporangium rusts.

Fungicides treatments are also available to control Gymnosporangium rusts, although such treatments should be considered only as a last resort. Among fungicides marketed for use by home gardeners, those containing chlorothalonil, copper, mancozeb, myclobutanil, propiconazole, and sulfur are labeled for use for Gymnosporangium rust control. These products may be useful for controlling Gymnosporangium rusts on rosaceous hosts, but will likely not be effective if used on junipers. For optimal control on rosaceous hosts, apply treatments when flower buds first show color, when half of the flowers are open, at petal-fall, seven to 10 days after petal fall and finally 10 to 14 days later. Be sure to read and follow all label instructions of the fungicide(s) that you select to ensure that you use the products(s) in the safest and most effective manner possible. In particular, be sure that you select appropriate products when treating trees and shrubs with edible fruit. If you decide to use propiconazole or myclobutanil, alternate use of these active ingredients with use of at least one of the other active ingredients listed above (but DO NOT alternate propiconazole with myclobutanil) to help minimize potential problems with fungicide-resistant strains of Gymnosporangium rust fungi.

For more information on Gymnosporangium rusts:

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

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 Laura Jull, Darrin Kimbler, Sharon Morrisey, Charlene Schmidt and Janet Van Zoeren 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, Disease - Herbaceous Ornamental, Disease - Needled Woody Ornamental, Disease - Vegetable, Misc

Wood Mulch and Tree Health

August 20, 2015 hudelson

UW Plant Disease Facts

Authors: Jane Cummings-Carlson and John Kyhl, Wisconsin Department of Natural Resources Gina Foreman and Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 03/02/2024
D-Number: D0128

What are the benefits of wood mulch?

Wood mulch is typically available as chipped wood, or shredded or chunked bark, and can contribute to tree health in many ways. When high quality, composted mulches are applied two to four inches deep in a ring three to six feet in diameter (or greater) from the trunk of a tree, mulch can help preserve moisture, control weeds, limit damage to the trunk from mowers and string trimmers and moderate the soil temperature. Use four inches of mulch when soils are light and well-drained, and two inches of mulch on heavier, clay soils.

Use of properly composted mulches can be beneficial to trees and shrubs in the landscape.

Can wood mulch harm trees?

Use of improperly composted mulches (some-times called “sour mulches”), can lead to tree nutrient deficiencies. Sour mulches can also produce gases like methane and ammonia that can be toxic to plants. Foliage on trees surrounded by sour mulches may initially turn yellow, then brown, die and fall off. If your mulch smells like vinegar, ammonia or sulfur, it is likely a sour mulch and should be removed. Replace the sour mulch with a high quality, composted mulch and consult with your local Extension agent about testing the soil for nutrient deficiencies. Fertilize appropriately based on the results of these tests.

Improper application of mulch can also lead to problems. Piling wood mulch up against the trunk of a tree can keep the bark underneath excessively wet. This wetness can contribute to bark decay. In addition, use of thick mulch layers (greater than four inches) can lead to overly wet soils that are favorable for development of root rots (see UW Plant Disease Facts D0094, Root and Crown Rot). To avoid these problems, make sure mulch is applied at least four inches away from the trunk of a tree and that the mulch layer is the appropriate thickness for the soil type in your landscape (see above).

Does woody mulch harbor or attract insects?

Insects such as earwigs [see UW Bulletin A3640, Controlling Earwigs (available at https://learningstore.extension.wisc.edu/)], centipedes (see University of Wisconsin Garden Facts XHT1113, Centipedes), millipedes (see University of Wisconsin Garden Facts XHT1108, Millipedes) and sowbugs (see University of Wisconsin Garden Facts XHT1110, Sowbugs) can feed on decaying organic matter in mulches. While these insects are often only nuisances, earwigs can feed on and cause damage to a variety of ornamentals, particularly to flowering plants. If mulch is used near entrances to a home or around basement windows, these unwanted insects may get inside. Termites ingest wood and can be attracted to wood mulch, but new termite colonies are not likely to become established due to use of wood mulches. Typically, termites are not a problem in Wisconsin, and when colonies are found, they occur only in the southern half of the state.

Carpenter ants [see UW Bulletin A3641, Controlling Carpenter Ants (available at https://learningstore.extension.wisc.edu/)] and powderpost beetles (see University of Wisconsin Garden Facts XHT1053, Powderpost Beetles) are unlikely to utilize mulch as a food source because conditions required for their development would not be satisfied by wood mulch. Carpenter ants do not ingest wood as a food source; instead, they chew non-living wood (in trees or landscape timbers, etc.) to excavate galleries in which they live and raise their young. Since wood mulch is composed of small wooden pieces, it would not serve as a home. To avoid potential insect problems, keep mulch as far away from the foundation of your home as possible and seal all holes and crevices that insects might use as entry points. Also, periodically inspect landscape timbers and the house for termites.

Does woody mulch harbor tree pathogens?

Wood mulch may come from many sources, including trees and shrubs that have died from a wide range of diseases. To be harmful to your trees, disease-causing organisms (pathogens) would have to survive in mulch and these organisms would have to move from the mulch either directly, or through the soil, to their new host – your tree. There is currently very little research on this topic.

Elm trees killed by Dutch elm disease (see UW Plant Disease Facts D0045, Dutch Elm Disease), can serve as breeding areas for native and European elm bark beetles. Bark beetles that breed in logs or firewood from these trees can pick up the fungi that cause Dutch elm disease (Ophiostoma ulmi and Ophiostoma novo-ulmi) and carry these fungi from tree to tree. Chipping infected elm trees creates an unfavorable environment for bark beetles yet there is no scientific literature that describes the level of risk of transmitting the Dutch elm disease fungi from wood chips or bark chunks to healthy elms.

Oak trees killed by oak wilt (see UW Plant Disease Facts D0075, Oak Wilt) can be attractive to several sap-feeding beetles that can potentially pick up the oak wilt fungus (Bretziella fagacearum) and move it in the landscape. This process is affected by moisture and temperature and would likely be disrupted by the chipping and composting process yet there is no scientific literature that describes the level of risk of transmitting the oak wilt disease fungus from wood chips or bark chunks to healthy oaks.

Research at the University of Wisconsin-Madison suggests that wood chip mulches produced from trees suffering from Verticillium wilt (see UW Plant Disease Facts D0121, Verticillium Wilt of Trees and Shrubs) can serve as a source of the fungus (Verticillium dahliae) that causes the disease. These studies show that Verticillium can survive for at least one year in mulch and that use of this contaminated mulch can lead to Verticillium wilt in both woody and herbaceous plants. Therefore use of mulches produced from trees with Verticillium wilt should be avoided.

For more information on wood mulch and tree health:

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 Ann Joy, Laura Jull and Phil Pellitteri 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 - Needled Woody Ornamental

Winter Burn

August 19, 2015 hudelson

UW Plant Disease Facts

Authors: Laura Jull, UW-Madison Horticulture

Last Revised: 03/02/2024

D-number: D0127

What is winter burn?

Winter burn is a common problem of evergreens including those with broad leaves (e.g., boxwood, holly, rhododendron), needles (e.g., fir, hemlock, pine, spruce, yew) and scale-like leaves (e.g., arborvitae, false cypress, juniper) grown in open, unprotected locations and exposed to severe winter conditions. Evergreen plants that are marginally hardy in a location (i.e., not well-adapted to local winter conditions) are at increased risk for winter burn. Winter burn can be so severe that affected plants may die and/or require replacement.

Browning due to winter burn on dwarf Alberta spruce.

What does winter burn look like?

Winter burn symptoms often become apparent as the snow melts and spring temperatures rise. Foliage starts to brown at the tips of branches with browning progressing inward toward the center of the plant. On broad-leaved evergreens, leaf edges typically brown first, followed by browning of entire leaves. Foliage facing south, southwest or west is most often affected. Symptomatic foliage often begins to drop off starting in spring and continuing through mid-summer as new foliage is produced. In extreme cases, entire plants can brown and die.

What causes winter burn?

There are many factors that can contribute to winter burn. In general, plants with shallow or poorly-developed root systems that do not efficiently take up water (e.g., recent transplants) are more prone to winter burn. Warm fall temperatures that delay the onset of plant dormancy can also contribute to winter burn. Under such conditions, plants are not prepared for the subsequent rapid onset of freezing winter temperatures, and as a result damage to foliage occurs. Similar cold injury can occur mid-winter when temperatures drop sharply at sunset causing foliage that has warmed during the day to rapidly cool and freeze. In addition, on sunny winter days, foliage (particularly foliage facing the sun) can begin to transpire (i.e., naturally lose water through the foliage). Because the ground is frozen, plant roots cannot take up water and replace the water that has been lost from the foliage. As a result, foliage dries and browns. Foliage under snow or facing away from the sun and direct winds is usually not damaged. Strong winter winds can lead to additional water loss making winter burn more severe. Colder than normal winter temperatures and longer than normal winters can also be factors in the development of winter burn, especially if below normal temperatures occur into April (the time of year when plants normally come out of dormancy and are most susceptible to winter injury). Finally, exposure of plants to salt used to de-ice roads, driveways and sideways during the winter can make plants more prone to winter burn injury.

How do I save a plant with winter burn?

For evergreens such as arborvitaes, boxwoods, junipers and yews, prune out dead, brown, damaged or dying tissue in mid-spring after new foliage is produced. If new foliage has not yet emerged by spring, scratch the bark on affected branches and look for green tissue underneath. Also gently peel back the bud scales to look for inner green bud tissue. If the stem or bud tissue is green, buds on the branch may still break to form new foliage. If the tissue is brown, the branch is most likely dead and you should prune the branch back to a live, lateral bud or branch. Such buds and branches may be far back inside the canopy and pruning may remove a substantial amount of the plant. Pines, spruces and firs typically produce new growth at branch tips in spring that will replace winter burn-damaged needles, and thus pruning may not be required on these evergreens. After a couple of growing seasons, new foliage will fill in the areas that were damaged. If an entire evergreen is brown, recovery is unlikely and the plant should be replaced with something (e.g., a deciduous shrub or tree) that is better-suited to the site.

How do I avoid problems with winter burn in the future?

Use a variety of strategies to prevent winter burn before winter arrives.

Plant the right plant in the right place.

Buy plants that are rated as cold hardy for your location and are well-adapted to local growing and soil conditions. Plants exposed to drying winter sun and winds are more likely to be injured. Therefore, avoid planting winter injury sensitive evergreens, particularly those that require shade or that are marginally cold-hardy, in exposed, sunny, windy areas. Plant them on the northeast or east side of a building or in a protected courtyard. Plant boxwoods, hemlocks, rhododendrons, and yews in partial shade to provide them added protection from winter sun and wind.

Plant evergreens at the right time of year.

Optimally, plant evergreens either in early spring (before buds break) or in late summer (i.e., August through September). Evergreens can be planted in the summer if you provide supplemental water. Avoid planting after early October in northern Wisconsin and after mid-October in southern Wisconsin as this will not allow sufficient time for roots to grow adequately before the ground freezes.

DO NOT prune evergreens in late summer or early fall.

Late season pruning of some non-native evergreens may encourage a flush of new growth that will not harden off properly before winter. See University of Wisconsin Garden Facts XHT1013, Pruning Evergreens, for details on when and how to prune specific evergreen trees and shrubs.

Mulch evergreens properly.

Apply two inches (on clay soils) to four inches (on sandy soils) of loose mulch (e.g., shredded hardwood, pine, or cedar bark; leaf compost; or wood chips) around the base of evergreens out to at least the drip line (e.g., the edge of where the branches extend). Keep mulch at least four inches away from the trunks of trees and the bases of shrubs. Proper mulch insulates roots from severe fluctuations of soil temperatures and reduces water loss. It also helps protect roots from injury due to heaving that occurs when soils go through cycles of freezing and thawing during the winter. Heaving can especially be a problem for shallow-rooted and newly planted evergreens. DO NOT mulch excessively or too close to plants as this can lead to damage by providing shelter for mice and voles (which can girdle trunks and branches) and by providing a favorable environment for disease development as well as insect activity and feeding.

Water plants properly.

Plants that are well-hydrated are less prone to winter burn. In particular, newly planted or young evergreens, especially those planted in open, exposed sites, those planted under eaves, or those planted in dry falls may suffer severe moisture loss during the winter and consequently severe winter burn. Established evergreens should receive approximately one inch of water per week and newly transplanted evergreens up to two inches of water per week during the growing season up until the soil freezes in the autumn or there is a significant snowfall. If supplemental watering is needed, use a soaker or drip hose to apply water near the drip lines of plants rather than using a sprinkler.

Avoid late summer or fall fertilization.

Applying quick-release, high-nitrogen fertilizers in late summer or fall could potentially stimulate growth of new foliage (particularly on some non-native evergreens) as well as inhibit proper onset of dormancy which can lead to damage over the winter. If you are concerned that your evergreens may need to be fertilized, submit a soil sample from around your plants to a professional soil testing lab that can provide specific information on what fertilizer to use and when to fertilize.

Protect plants during the winter.

Use burlap, canvas, snow fencing or other protective materials to create barriers that will protect plants from winter winds and sun. Install four to five foot tall stakes approximately two feet from the drip lines of plants especially on the south and west sides (or any side exposed to wind) and wrap protective materials around the stakes to create “fenced” barriers. Leave the top open. These barriers will deflect the wind and protect plants from direct exposure to the sun. Remove the barrier material promptly in spring. DO NOT tightly wrap individual plants with burlap as this can collect ice, trap moisture and make plants more susceptible to infection by disease-causing organisms. Use of anti-transpirant products to prevent water loss from foliage over the winter has been shown to have limited benefit. These materials degrade rapidly, require reapplication after each significant rain or snow event, and may not be effective in preventing water loss that can lead to winter burn.

For more information on winter burn:

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 Linda Chalker – Scott, Bert Cregg and Jean Ferdinandsen 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 - Fruit Crop, Disease - Needled Woody Ornamental

White Pine Blister Rust

August 19, 2015 hudelson

UW Plant Disease Facts

Authors: Joseph Schwartz, UW-Madison Forest Ecology and Management and Glen R. Stanosz, Ph. D., UW Madison Plant Pathology

Last Revised: 03/02/2024

D-number: D0126

What is white pine blister rust?

White pine blister rust is a serious, tree-killing disease of eastern white pine and its close relatives (pines with needles in bundles of five). This disease is caused by the exotic (non-native) fungus Cronartium ribicola, which was introduced into North America in the early 1900’s. This pathogen is now found in most regions where pines grow in the United States, including Wisconsin. White pine blister rust affects trees of all ages, but perhaps most frequently and severely damages seedlings and saplings.

White pine blister rust cankers on branches and stems often have a cracked or blistered appearance and may bear yellow to orange spores in fruiting bodies of Cronartium ribicola.

Where does white pine blister rust come from?

White pine blister rust is caused by the fungus Cronartium ribicola, which requires two different plant hosts to complete its complex life cycle. Spores of the fungus produced on white pine are blown to alternate host plants in the genus Ribes (gooseberries and currants). After infecting gooseberry and currant bushes the fungus multiplies rapidly throughout the summer, repeatedly producing spores that germinate to result in additional gooseberry and currant infections. Spores produced in late summer on gooseberries and currants are spread by the wind to white pines, where needles that are moist from rain, fog, or dew are infected.

What does white pine blister rust look like?

Infection of needles by Cronartium ribicola results in development of yellow to brown spots and bands. The fungus slowly grows through pine needles and bark to eventually form cankers on twigs, branches, and trunks of trees. A canker is a localized diseased area (either swollen or sunken) that is surrounded by healthy tissues. A typical white pine blister rust canker has resinous margins, and may appear “blistered” before rupturing to expose fruiting bodies (reproductive structures) with yellow to bright orange spores of Cronartium ribicola. As a canker expands to completely encircle stems, all parts of the plant beyond the canker are killed. Dead white pine branches may temporarily retain their orange to red dead needles to form a bright “flag” that is a common symptom of this disease.

Can I save a tree affected by white pine blister rust?

There is no “cure” for a tree with a white pine blister rust canker on its main trunk or stem. As the canker expands to completely encircle the trunk, all parts above the canker will die. Branch cankers that extend to within four inches of the trunk, probably indicate that the trunk already is colonized by the fungus and future development of a main stem canker is likely. Pruning off branches on which cankers are located farther from the trunk, however, can prevent the fungus from growing into the trunk. These branch cankers can be removed by pruning at least six inches beyond any visible symptoms on the trunk side of the cankered branch. Removal of branch cankers and trees with main stem cankers prevents production of spores that are spread to gooseberries and currants. The fungus quickly dies in discarded branches and trunks and presents no further danger to either of its hosts.

How do I avoid future problems from white pine blister rust?

Infection of pine is most frequent near diseased gooseberries or currants. Therefore, removing these plants (especially within 200 feet) can greatly reduce the incidence of white pine blister rust. Gooseberries or currants can be killed by uprooting them or by application of herbicides in accordance with label directions.

Conditions that promote or prolong needle wetness should be avoided. These include use of sprinklers that wet the needles of ornamental trees, dense plantings, growth of weeds surrounding young trees, or planting white pines in low-lying, chronically moist areas near water or sites that lack good air movement. Growing white pines under a hardwood overstory that will intercept evening dew can help keep needles dry and reduce infection.

Regular inspection allows prompt detection and removal of cankered branches on young trees. Also, because infection very often occurs on needles of low branches, pruning to remove healthy branches (if aesthetically acceptable) will reduce the likelihood of this disease. When trees are five to seven years old, starting close to the ground, prune off all branches up to no more than one-third to one-half the height of the tree. Branch pruning can be continued every other year until the lower eight to nine feet of trunk is free of branches.

Planting or measures to encourage natural regeneration of conifer species other than white pines (including red or jack pines, spruces, firs, arborvitae, hemlock, and junipers) might be considered, especially where gooseberries or currants are prevalent and where moisture conditions favor infection.

Application of protectant fungicides may be a useful management practice in white pine production nurseries. Nursery stock should be carefully inspected, particularly just prior to sale, because the planting of diseased white pine seedlings is one way Cronartium ribicola has been spread into previously disease-free locations.

For more information on white pine blister rust:

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 Ann Joy and Brian Hudelson 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, Pest Alerts

Weir’s Cushion Rust of Spruces – Pest Alert

August 19, 2015 hudelson

UW Plant Disease Facts

Pest Alert

Authors: Glen R. Stanosz, UW Madison Plant Pathology, and Forest Ecology and Management

Last Revised: 03/02/2024

D-number: D0124

What is Weir’s cushion rust?

Weir’s cushion rust is a needle disease that disfigures and reduces growth of spruce trees (Picea spp.) of all ages. This disease has been known in both eastern and western regions of the United States, but was recognized in Wisconsin for the first time in 2002.

Yellow spots and bands in winter on spruce shoots affected by Weir's cushion rust. — Yellow spots and bands in winter on spruce shoots affected by Weir’s cushion rust.

What does Weir’s cushion rust look like?

Needles on current year’s shoots affected by Weir’s cushion rust may develop yellow spots or bands in the summer and fall. These spots and bands may intensify to give needles a bright “green and gold” appearance the following spring, when tiny blister-like pustules (a type of fungal reproductive structure) develop in the yellow areas. Microscopic examination of these pustules is required for diagnosis of the disease. Affected one-year-old needles continue to yellow, turn brown, and fall off as the spring and summer progress. Trees badly damaged by Weir’s cushion rust will have thin crowns due to repeated loss of the previous year’s needles.

Where does Weir’s cushion rust come from?

Weir’s cushion rust results from colonization of spruce needles by the fungus Ceropsora weirii (formerly Chrysomyxa weirii). This fungus overwinters in needles infected during the previous growing season. In late summer, or more typically the following spring, C. weirii produces spores in the pustules that develop on the needles. These spores can be blown by wind or splashed by rain to newly emerging needles on the same tree or other trees. Spore germination is followed by infection of young needles.

Can I save a tree affected by Weir’s cushion rust?

Apply fungicides containing chlorothalonil to trees affected by Weir’s cushion rust to prevent new needle infections. Make the first application when 10% of the buds have broken and two additional applications at seven to 10 day intervals thereafter. Fungicide applications do not kill the fungus in needles that are already infected, so be sure to begin applications promptly and complete the spray program, to ensure thorough coverage and protection of new foliage. Please be sure to read and follow all fungicide label instructions to ensure that you use the product in the safest and most effective manner possible. Needles infected by C. weirii eventually die. The fungus does not continue to live or produce spores on these dead needles. Therefore, destruction of dead needles is not necessary.

How do I avoid Weir’s cushion rust in the future?

DO NOT accept and plant landscape or nursery stock affected by Weir’s cushion rust. Inspect established spruce trees (in both landscape and nursery settings) in late summer and fall for evidence of Weir’s cushion rust (e.g., yellow spots and bands on the current year’s needles). Inspect suspect trees again in spring for these symptoms, as well as pustules of C. weirii on the previous year’s needles. In nurseries, move affected trees to areas where the disease is not already present. Use fungicide applications to prevent establishment of the fungus on new trees or in previously unaffected nurseries and landscapes.

For more information on Weir’s cushion rust:

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 Brian Hudelson 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

Swiss Needle Cast

August 18, 2015 hudelson

UW Plant Disease Facts

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

Last Revised: 03/02/2024

D-number: D0109

What is Swiss needle cast?

Swiss needle cast is a fungal disease of Douglas-fir. This tree is native to the Rocky Mountains and the Pacific Coast but has been grown in Wisconsin as a landscape ornamental and as a Christmas tree. Swiss needle cast can limit the aesthetic appeal of Douglas-fir grown in landscape settings, as well as the marketability of Douglas-fir grown in Christmas tree production.

Fruiting bodies of the Swiss needle cast fungus on the undersides of needles.

What does Swiss needle cast look like?

Infected needles become discolored (blotchy yellow-green or completely yellow) and then brown from the tips. Older needles are more severely affected than younger needles. Brown needles drop prematurely, leaving twigs with only the newest growth. Using a hand lens, small, black reproductive structures of the Swiss needle cast fungus can be seen in two diffuse bands on the undersurface of infected needles.

Where does Swiss needle cast come from?

Swiss needle cast is caused by the fungus Nothophaeocryptopus gaeumannii. Spore production, needle infection, and symptom development are favored by wet environmental conditions (e.g., rainy weather). Infections primarily occur on new needles as they emerge and expand in the spring. Fully expanded needles are less susceptible to infection. Once infection has occurred, fruiting bodies (i.e., reproductive structures) form and produce spores on both discolored and green needles. Spores may be produced for several seasons before needles drop.

How can I save a tree with Swiss needle cast?

Infected needles cannot be cured. However, fungicide sprays containing chlorothalonil or mancozeb may help prevent additional infections on small trees where complete, uniform coverage is possible. Fungicide treatments are not recommended for large trees. For plantation and landscape trees, apply two fungicide applications, the first when buds are ½ to two inches long, and the second about three weeks later. In the more stressful environment of nurseries, trees may require sprays every two weeks through mid-August. Using preventive treatments, infected trees may regain their lush, full look within two years. 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 can I prevent Swiss needle cast in the future?

Use Douglas-firs grown from seed originating in Pacific Coast areas rather than those grown from seed originating in the Rocky Mountains. Pacific Coast trees appear to be less susceptible to Swiss needle cast. Also, use resistant and tolerant varieties where available. Purchase stock from a reputable nursery; Nothophaeocryptopus gaeumannii is often spread through infected nursery stock. When planting Douglas-firs, choose a site that has well-drained, but moist soil with a neutral to slightly acidic pH and allow adequate spacing between trees to promote increased airflow and quicker drying of needles. This drier environment is less favorable for infection and disease development. Make sure trees have sufficient water and are fertilized properly (based on soil and needle nutrient tests) to reduce stress that may increase trees’ susceptibility to Swiss needle cast.

For more information on Swiss needle cast:

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 Diana Alfuth, Thad Kohlenberg, 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/.

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

Root and Crown Rots

August 15, 2015 hudelson

UW Plant Disease Facts

Authors: Brian Hudelson, UW-Madison Plant Pathology and Laura Jull, UW-Madison Horticulture

Last Revised: 03/01/2024

D-number: D0094

Discoloration of maple crown and roots typical of Phytophthora root/crown rot.

What is root/crown rot?

Root/crown rot is a general term that describes any disease of woody ornamentals where the pathogen (causal organism) attacks and leads to the deterioration of a plant’s root system and/or lower trunk or branches near the soil line. Root rots can be chronic diseases or, more commonly, are acute and can lead to the death of the plant.

What does root/crown rot look like?

Gardeners often become aware root/crown rot when they see above ground symptoms. Affected plants are often slow-growing or stunted and may show signs of wilting. Often the canopy of an affected tree or shrub is thin, with foliage that is yellow or red, suggesting a nutrient deficiency. Careful examination of the roots/crowns of these plants reveals tissue that is soft and brown.

Where does root/crown rot come from?

Several soil-borne water molds (i.e., fungi-like organisms) and true fungi can cause root/crown rots, including (most frequently) Phytophthora spp. and Pythium spp. (both water molds), and Rhizoctonia solani and Fusarium spp. (both true fungi). These organisms have wide host ranges, and prefer wet soil conditions. Water mold root rot organisms such as Pythium and Phytophtora produce thick-walled spores (called oospores) that can survive for long periods (years to decades) in soil.

How do I save a plant with root/crown rot?

REDUCE SOIL MOISTURE! Provide enough water to fulfill a plant’s growth needs and prevent drought stress, but DO NOT over-water. Remove excess mulch (greater than four inches) around trees and shrubs. Excessive mulch can lead to overly wet soils.

A thinning canopy with red or yellow leaves can indicate a root/crown rot problem.

Chemical fungicides (e.g., PCNB, mefenoxam, metalaxyl, etridiazole, thiophanate-methyl and propiconazole) and biological control agents (e.g., Gliocladium, Streptomyces, and Trichoderma) are labeled for root/crown rot control. However, DO NOT use these products unless you know exactly which root/crown rot pathogen(s) is(are) affecting your trees and shrubs. Contact your county Extension agent for details on obtaining an accurate root/crown rot diagnosis and for advice on which, if any, fungicides you should consider using.

How do I avoid problems with root/crown rots?

Buy plants from a reputable source, and make sure they are root/crown rot-free prior to purchase. Establish healthy plants in a well-drained site, and when planting, place the root collar just at the soil surface. To moderate soil moisture, add organic material (e.g., leaf litter or compost) to heavy soils to increase soil drainage, and DO NOT over-water. Also, DO NOT apply more than three inches of mulch around trees and shrubs, and keep mulch from directly contacting the base of trunks and stems. Prevent physical damage (e.g., lawnmower injury) that can provide entry points for root/crown rot pathogens. Finally, minimize movement of root/crown rot fungi in your garden. DO NOT move soil or plants from areas where plants are having root/crown rot problems. DO NOT water plants with water contaminated with soil (and thus potentially with root/crown rot organisms). After working with plants with root/crown rot, decontaminate tools and footwear by treating for at least 30 seconds with a 10% bleach solution or 70% alcohol (e.g., rubbing alcohol, certain spray disinfectants). If you use bleach to decontaminate metal tools, be sure to thoroughly rinse and oil your tools after you are done gardening to prevent rusting.

For more information on root/crown rots:

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, Ann Joy and Sharon Morrisey 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

Phytophthora Root Rot of Christmas Trees

July 31, 2015 hudelson

UW Plant Disease Facts

Authors: Ann Joy, UW-Madison Plant Pathology and Anette Phibbs, Wisconsin Department of Agriculture, Trade and Consumer Protection (WI DATCP)

Last Revised: 03/01/2024

D-number: D0079

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.

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 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 Bryan Jensen, Laura Jull, and Brooke Sanneh 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

Phomopsis Tip Blight

July 31, 2015 hudelson

UW Plant Disease Facts

Authors: Gina Foreman* and Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 03/01/2024

D-number: D0077

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.

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 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 Plant Pathology 875 – Plant Disease Diagnostics Clinic Internship at the University of Wisconsin Madison.

Thanks to Karen Delahaut, Lis Friemoth 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.

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

Nectria Canker

July 29, 2015 hudelson

UW Plant Disease Facts

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

Last Revised: 03/01/2024

D-number: D0074

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.

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:

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, Laura Jull, and Bob Tomesh 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/.