All posts by hudelson

Cytospora Canker

July 19, 2015 hudelson

UW Plant Disease Facts

Authors: Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0037

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.

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:

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).

Thanks to Diana Alfuth, Jean Ferdinandsen, Lisa Johnson, Amy Sausen 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 - Broad Leafed Woody Ornamental, Disease - Fruit Crop, Disease - Herbaceous Ornamental, Disease - Vegetable

Crown Gall

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: D0035

What is a crown gall?

Crown gall is the most widely distributed bacterial disease of plants in the world, affecting over 100 species of fruit crops, and woody and herbaceous ornamentals, including rose, euonymus, lilac, poplar, viburnum, willow, apple, pear, brambles, stone fruits and grapes. Crown gall can cause severe damage on young plants, while mature woody plants with the disease may show no ill effects.

Crown gall leads to tumor-like growths that form at or near the soil line.

What does crown gall look like?

Crown gall gets its name from the round or irregularly shaped tumor-like growths (i.e., galls) that usually form on plant crowns just above or below the soil line. Galls can also form on roots, stems, trunks, or branches. Galls can be pea-sized, or as large as several inches in diameter. Galls interfere with water transport within the plant. Therefore, affected plants may suffer from water or nutrient deficiencies, becoming stunted. Flower and fruit production may also be reduced.

Where does crown gall come from?

Crown gall is caused primarily by the bacteria Agrobacterium tumefaciens, as well as (on grape) by A. vitis. Both bacteria survive in soil and in (or on) susceptible plant roots. The bacterium is spread through movement of contaminated soil, water and infected plant material. The bacterium enters plants through wounds (e.g., mechanical injuries including pruning cuts, freeze injury, and nematode feeding sites) or natural plant openings (e.g., lenticels) and stimulates plant cells to undergo unregulated growth, leading to gall formation. Once galls begin to form, they can continue to enlarge even if the bacterium is no longer present. Galls become visible anywhere from several weeks to one or more years after the time of infection.

How do I save a plant with crown gall?

There is no cure for crown gall once galls begin to form. Galls can be pruned away, but new galls may reform elsewhere on the plant. To prevent spread of the crown gall bacterium, remove infected plants, surrounding soil, and as many of the infected plant’s roots as possible.

How do I avoid problems with crown gall in the future?

Use disease-free, winter hardy stock from a reputable nursery and inspect the roots and crowns for galls before planting. Avoid wounding plants during transplant and cultivation. Decontaminate tools, equipment and shoes with 10% bleach or 70% alcohol for at least 30 seconds to prevent spread of the bacterium. Use of a biological control product can prevent A. tumefaciens infections at the time of planting. Current biological control products contain A. radiobacter, a close relative of the crown gall organism. These products are not effective on all hosts, or against all variants of the pathogen. In areas with infested soil, rotation to a non-susceptible plant (such as grass) for 3 years, may provide a good means of disease control. In commercial settings, soil fumigation may provide limited control of the crown gall bacterium in soil. However, fumigation does not kill the bacterium in roots that remain in the soil after removal of infected plants. Fumigation is not recommended for homeowners.

For more information on crown gall:

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

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 Diana Alfuth, Paul Hartman, and Patty McManus 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, Disease - Vegetable

Corky Ringspot

July 14, 2015 hudelson

UW Plant Disease Facts

Authors: Brian Hudelson and Amy Charkowski, UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0034

What is corky ringspot?

Corky ringspot (also known as spraing) is a potentially serious viral disease of potato that has recently been detected in Wisconsin. The disease can cause severe losses due to the fact that it reduces potato tuber quality, making tubers unsuitable for use in potato chip production and undesirable to consumers as table stock. Variants of this disease [usually referred to as tobacco rattle (see UW Plant Disease Facts D0116, Tobacco Rattle)] affect a variety of other plants including vegetable crops (e.g., beans, beets, peppers, and spinach), many herbaceous ornamentals (e.g., astilbe, bleeding heart, coral bells, daffodil, epimedium, gladiolus, hyacinth, marigold, tulip, and vinca) and many weed species (e.g., chickweed, cocklebur, henbit, nightshade, pigweed, purslane, prickly lettuce, shepherd’s-purse and sowthistle).

Internal necrosis of tubers, often in fleck or arc patterns is typical of corky ringspot.

What does corky ringspot look like?

Symptoms of corky ringspot vary depending on the variety/cultivar of potato affected, and depending on environmental conditions. Foliar symptoms are rare, but on occasion can include reduced leaf size, puckering and mottling (i.e., blotchy light and dark coloring). More commonly, corky ringspot manifests itself underground as corky arcs, rings or flecks that form on or within tubers. Thinner-skinned and lighter-colored potato varieties are more likely to exhibit obvious ring symptoms on the surfaces of tubers. Symptoms similar to those caused by corky ringspot can be caused by other potato viruses such as alfalfa mosaic virus, potato mop-top virus, and certain strains of potato virus Y.

Where does corky ringspot come from?

Corky ringspot is caused by the Tobacco rattle virus (TRV) which is spread primarily by stubby-root nematodes, a group of microscopic, worm-like organisms in the genera Trichodorus and Paratrichdorus. These nematodes feed on the roots of infected plants (vegetables, ornamentals or weeds), acquiring TRV, then move to non-infected plants where their subsequent feeding spreads the virus. TRV also can be spread mechanically when knives or other tools that are used to cut tubers for seed pieces, or that are used to divide ornamental plants, become contaminated. In addition, on ornamentals, TRV can be spread by pruning and grafting, and via movement of seed from infected plants.

How do I save potatoes with corky ringspot?

Once potatoes have become infected with TRV, they remain infected indefinitely. Infected plants cannot be treated in any way to eliminate the virus and should be removed and disposed of by burning (where allowed by local ordinance), burying or composting. Before destroying symptomatic plants, you may want to have them tested to verify the presence of TRV. Note that ELISA (a technique commonly used to test for other potato viruses) is not a reliable test for TRV; polymerase chain reaction (PCR) should be used to test for this virus. Once TRV is introduced into a field, it is likely to remain there indefinitely. Stubby-root nematodes can carry the virus for extended periods and weed species can serve as reservoirs of the virus indefinitely.

Tubers with corky ringspot may, but do not always have target-like ring patterns on their surfaces.

How do I avoid problems with corky ringspot in the future?

The best way to prevent problems with corky ringspot is to avoid introducing TRV onto your property. Be sure to grow potatoes from seed that is certified as being free of TRV. Currently, seed potatoes produced in Wisconsin are considered TRV-free. Also avoid introducing the virus on infected ornamental plants. Carefully inspect ornamentals (see above for a partial list of susceptible species) prior to purchase for symptoms caused by TRV and DO NOT buy symptomatic plants. Alternatively (and preferably), avoid growing susceptible species altogether, and grow plants that are not susceptible to TRV. Non-susceptible plants include, but are not limited to, annual phlox, carnation, carrot, devil’s trumpet (downy thorn-apple), Scotch spearmint, sorrel, sweet William, zinnia and zombie cucumber.

To limit potential spread of TRV, routinely decontaminate tools (e.g., knifes or other cutting tools) that come into contact with potentially infected plant material (e.g., whole tubers that are cut into seed pieces, or ornamentals that are being divided). Also decontaminate tires, tools (e.g., spades or hoes) and any other object (e.g., shoes or boots) that might transport stubby-root nematode-infested (and thus TRV-infested) soil from field to field. First rinse any excess plant tissue or soil from these items, then treat them for at least 30 seconds in a solution that is a combination of 1% sodium lauryl sulfate and 1% Alconox (an industrial detergent). Trisodium phosphate (available at most local hardware stores) can also be used.

Also consider routinely testing soils for the presence of stubby root nematodes. Knowing the level of these nematodes in a field can provide information on the likelihood that TRV will spread should the virus be introduced.

Finally, DO NOT ever produce seed potatoes in fields with a history of corky ringspot or other TRV diseases. Also avoid using infested fields for potato or other vegetable production. If you decide to use a TRV-infested field for non-seed potato production, be sure to grow a TRV-resistant potato variety. The potato varieties ‘Castile’, ‘Millennium Russet’, ‘Red Pearl’, ‘Symfonia’, and ‘St. Johns’ have all been reported to have at least moderate levels of resistance to TRV.

For more information on corky ringspot:

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 Tom German, Amanda Gevens and Russell Groves 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, Disease - Vegetable

Common Corn Smut

July 14, 2015 hudelson

UW Plant Disease Facts

Authors: Tianna Jordan*, UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0031

Common corn smut leads to tumor-like galls on corn filled with a sooty, black powder.

What is common corn smut?

Common corn smut is a fungal disease that affects field, pop, and sweet corn, as well as the corn relative teosinte (Zea mexicana). Common corn smut is generally not economically significant except in sweet corn where relatively low levels of disease make the crop aesthetically unappealing for fresh market sale and difficult to process for freezing or canning. Interestingly, the early stages of common corn smut are eaten as a delicacy in Mexico where the disease is referred to as huitlacoche (see UW Plant Disease Facts D0065, Huitlacoche).

What does common corn smut look like?

Common corn smut leads to tumor-like swellings (i.e., galls) on corn ears, kernels, tassels, husks, leaves, stalks, buds and, less frequently, on aerial roots. Some galls (particularly those on leaves) are small and hard. More typically, however, galls are fleshy and smooth, silvery-white to green, and can be four to five inches in diameter. As fleshy galls mature, their outer surfaces become papery and brittle, and their inner tissues become powdery and black. Galls eventually rupture, releasing the powder (i.e., the spores of the causal fungus).

Where does common corn smut come from?

Common corn smut is caused by the fungus Ustilago maydis, which can survive for several years as spores in soil and corn residue. Spores are spread by wind or through water splashing up onto young plants. Spores can also be spread through the manure of animals that have eaten infected corn. U. maydis most typically infects corn ears via the silks. The fungus can also enter plants through wounds caused by insect feeding, hail, or injuries from machinery. Infection is favored by warm weather (79-93°F) and moderate rainfall. Corn grown in low fertility soils or soils with excessive nitrogen also has a greater likelihood of infection.

How do I save plants with common corn smut?

Once galls have formed, treatment is not possible. Remove and burn (where allowed by local ordinance) or bury smut galls before they burst to prevent spores from spreading and overwintering. In order for eradication to be effective, you will need to coordinate efforts with your neighbors. Fungicides are currently not an effective control against common smut.

How do I avoid problems with common corn smut in the future?

Plant resistant corn varieties whenever possible. Check with your favorite sweet corn seed supplier for available varieties. Also, avoid injuring plants (e.g., when weeding) to reduce possible entry points for the smut fungus. Maintain well-balanced soil fertility (specifically nitrogen) based on a soil nutrient test. Use crop rotation (see University of Wisconsin Garden Facts XHT1210, Using Crop Rotation in the Home Vegetable Garden for details) to allow time for corn smut spores to naturally die off in the soil.

For more information on common corn smut:

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 558 at the University of Wisconsin Madison.

Thanks to Allyse Engle, Nancy Engle, Taylor Jordan, Nicholas O’Connor, Chris Parise, Karen Schleis and Trisha Wagner 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 - Herbaceous Ornamental, Disease - Needled Woody Ornamental

Chlorosis

July 14, 2015 hudelson

UW Plant Disease Facts

Authors: Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0030

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.

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 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 Sharon Morrisey, Patti Nagai 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 - Field and Forage

Charcoal Rot of Soybean

July 14, 2015 hudelson

UW Plant Disease Facts

Pest Alert

Authors: Carol Groves and Damon Smith, UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0029

What is charcoal rot?

Charcoal rot, also known as summer wilt or dry weather wilt, is a fungal disease of soybean that most commonly occurs in plants that are under heat and water stress. Charcoal rot is most prevalent in the southern United States, but can occur in the North Central region when weather is hot and dry. In Wisconsin, charcoal rot is observed most often in fields with sandy soils.

A dusty, gray discoloration of stems and roots is characteristic of charcoal rot of soybean. (photo courtesy of Theresa Hughes)

What does charcoal rot look like?

Plants suffering from charcoal rot may display premature yellowing of their top leaves, as well as premature leaf drop that may be mistaken for normal plant maturity. Plants with charcoal rot often initially wilt in the midday heat and then recover at night. Eventually permanent wilting will occur. In some cases, the upper third of a plant may have unfilled, flat seedpods. At flowering, a light gray discoloration develops in the surface tissues of both tap and secondary roots, as well as lowers stems. These tissues will appear as if they have been dipped in charcoal dust, hence the name of the disease. The dusty appearance is due to the presence of tiny survival structures (called microsclerotia) of the fungus that causes the disease.

Where does charcoal rot come from?

Charcoal rot is caused by the fungus Macrophomina phaseolina which has an extensive distribution and is known to infect over 500 plant species including corn (where it causes charcoal stalk rot), alfalfa, and many ornamental and weed species. M. phaseolina can survive for two or more years in dry soils as microsclerotia embedded in plant residue. In wet soils however, microsclerotia do not survive for more than seven to eight weeks. Hyphae (i.e., fungal threads) of the fungus typically do not survive in soil for more than seven days. Infections of M. phaseolina primarily occur in the spring when soil moisture is high. The fungus enters plants via roots and then grows very slowly until plants reach their reproductive stage (usually coinciding with the hottest, driest part of the growing season). Then more extensive colonization of plant tissue occurs. M. phaseolina is most active when soil temperatures are high (80 to 95°F), unlike many other soilborne, disease-causing fungi, which have reduced activity when soil temperatures are high.

How can I save a soybean crop with charcoal rot?

By the time that typical symptoms of charcoal rot are evident, control of charcoal rot is difficult, and losses in yield are likely inevitable. Foliar fungicides and fungicide seed treatments have no effect on charcoal rot.

How can I avoid problems with charcoal rot in the future?

Plant high quality, pathogen-free seed to prevent introduction of the charcoal rot pathogen into fields that are not currently infested. In fields where M. phaseolina is already present, any cultural practices that minimize plant stress will reduce the risk of charcoal rot. Use tillage practices (e.g., no-till) that maintain soil moisture, and irrigate where possible during dry periods to reduce drought stress. Lower plant populations and maintain good weed control to minimize stress from competition for soil nutrients. In addition, optimize soil fertility levels, particularly phosphorus. Rotations with wheat may provide some control of charcoal rot. However, because M. phaseolina has a wide host range (including corn), crop rotation may not provide sufficient control of charcoal rot. A moderate level of partial resistance is known in soybean varieties in maturity groups IV and higher. Unfortunately these varieties are not suitable for production in Wisconsin. Whether partial resistance is present in commercial varieties suitable to be grown in Wisconsin (maturity groups I and II) is not known.

For more information on charcoal rot of soybean:

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 Craig Grau, Kevan Klingberg 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 agriculture-related questions at https://extension.wisc.edu/agriculture/ask-an-agriculture-question/.

Disease - Broad Leafed Woody Ornamental

Butternut Canker

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Rachel Leisso*, Montana State University Plant Sciences and Plant Pathology Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0027

What is butternut canker?

Butternut canker is a fungal disease of Juglans cinerea, the butternut tree (also known as white walnut or oilnut). The disease is thought to have originated outside of the U.S. The first documented case of butternut canker in Wisconsin occurred in 1967. Butternut canker affects butternuts throughout their natural range (much of the eastern US) and has killed up to 80% of the butternut trees in some states. Although butternut canker can occur on saplings of black walnut (Juglans nigra), the effects of the disease on this species are minimal.

Multiple butternut cankers on a butternut tree trunk can girdle and kill the tree.

What does butternut canker look like?

Infected areas (called cankers) tend to be most noticeable on large branches or tree trunks, where long fissures in the bark form. Several cankers may grow together leading to bark that is distorted and has a mangled appearance. Smaller cankers also form around leaf or branch scars. These cankers are sunken and black, with white margins and folds of bark around the edge. Cankers girdle branches and trunks, cutting off nutrients and water, leading to progressive dieback above the canker. Trunk cankers will eventually kill trees. A single trunk canker can kill a young sapling, while several cankers combined may be needed to kill an older tree.

Where does butternut canker come from?

Butternut canker is caused by the fungus Ophiognomonia clavigignenti-juglandacearum. Spores of the fungus are produced in cankers throughout the growing season and are spread from infected to healthy trees through rain-splash, insects, and wind. Wounds, as well as leaf and branch scars, often serve as points of entry for the fungus. Once a tree is infected, additional infections can occur as spores are washed by rain down to the main trunk of the tree.

How do I save a tree with butternut canker?

There is no cure for butternut canker. Trees with trunk cankers will most likely die. If branch cankers are found early, removal of the affected branches can prevent the spread of the disease to other parts of the tree. Prune out smaller branch cankers by cutting six to eight inches below the canker. Disinfect pruning tools after each cut by treating them for at least 30 seconds with a 10% bleach solution or preferably (because of its less corrosive properties) a 70% alcohol solution (e.g., rubbing alcohol or certain spray disinfectants). If you use bleach, be sure to thoroughly rinse and oil tools after pruning to prevent rusting.

How do I avoid problems with butternut canker in the future?

There is little that you can do to prevent butternut canker. However, vigorously growing butternut trees are better able to slow the development of butternut canker, so make sure that trees are watered and fertilized properly. Established trees require approximately one inch of water per week. If natural rains do not provide this amount of water, consider applying supplemental water near the drip line of the tree using a drip or soaker hose. Fertilization of trees should be based on a soil nutrient test.

If you live in a region where butternut canker is not currently present, or where there are few butternut trees, your butternut tree may be free of cankers indefinitely. If you live in a region where butternut canker is prevalent, watch for trees that are not affected by the disease. These trees may have inherent resistance. Consider collecting seed from such trees and growing saplings from the seed. At least some of these saplings will likely also have resistance to the disease.

For more information on butternut 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

*Completed as partial fulfillment of the requirements for Plant Pathology 699 – Plant Pathology Special Topics at the University of Wisconsin-Madison.

Thanks to Diana Alfuth, Lis Friemoth and Vijai Pandian 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

Brown Stem Rot of Soybean

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Carol Groves and Damon Smith, UW-Madison Plant Pathology

Last Revised: 02/28/2024

D-number: D0026

What is brown stem rot?

Brown stem rot (BSR) is a disease of soybean that was first observed in central Illinois in 1944 and is now prevalent throughout the North Central States of the US, and Canada. BSR has been identified as the third most important disease of soybeans in Wisconsin, attributable to the expansion of soybean acreage and shorter crop rotations used in the state. The agronomic impact of BSR is greatest in high yield potential environments. BSR negates the benefits of management practices intended to increase yield potential.

Brown pith discoloration of soybeans suffering from brown stem rot (top) compared with the white pith of a healthy soybean plant (bottom). (photo courtesy of Craig Grau)

What does brown stem rot look like?

Symptoms of BSR are usually not evident until late in the growing season and may be confused with signs of crop maturity or the effects of dry soils. The most characteristic symptom of BSR is the brown discoloration of the pith especially at and between nodes near the soil line. This symptom is best scouted for at full pod stage. Foliar symptoms, although not always present, typically occur after air temperatures have been at to below normal during growth stages R3-R4, and often first appear at stage R5, peaking at stage R7. Foliar symptoms include interveinal chlorosis and necrosis (i.e., yellowing and browning of tissue between leaf veins), followed by leaf wilting and curling. Yield loss as a result of BSR is generally greatest when foliar symptoms develop. The severity of BSR symptoms increases when soil moisture is near field capacity (i.e., when conditions are optimal for crop development).

Foliar symptoms of BSR can be confused with those of sudden death syndrome (see UW Plant Disease Facts D0107, Sudden Death Syndrome of Soybean). However, in the case of sudden death syndrome (SDS), the pith of affected soybean plants will remain white or cream-colored. In addition, roots and lower stems of plants suffering from SDS (but not those suffering from BSR) often have light blue patches indicative of spore masses of the fungus that causes SDS.

Where does brown stem rot come from?

BSR is caused by the soilborne fungus Phialophora gregata. There are two distinct types (or genotypes) of the fungus, denoted Type A and Type B. Type A is the more aggressive strain and causes more internal damage and plant defoliation than Type B. P. gregata Type A also is associated with higher yield loss.

P. gregata survives in soybean residue, with survival time directly related to the length of time that it takes for soybean residue to decay. Thus, P. gregata survives longer when soybean residue is left on the soil surface (e.g., in no-till settings) where the rate of residue decay is slow. P. gregata infects soybean roots early in the growing season. It then moves up into the stems, invading the vascular system (i.e., the water-conducting tissue) and interfering with the movement of water and nutrients.

Several factors can influence BSR severity. Research from the University of Wisconsin has shown that the incidence and severity of BSR is greatest in soils with low levels of phosphorus and potassium, and a soil pH below 6.3. In addition, P. gregata and soybean cyst nematode (Heterodera glycines) frequently occur in fields together, and there is evidence that BSR is more severe in the presence of this nematode.

Interveinal chlorosis and necrosis typical of brown stem rot. (photo courtesy of Craig Grau)

How can I save a soybean crop with brown stem rot?

BSR cannot be controlled once plants have been infected. Foliar fungicides and fungicide seed treatments have no effect on the disease.

How can I avoid problems with brown stem rot in the future?

Use crop rotations of two to three years away from soybean with a non-host crop (e.g., small grains, corn, or vegetable crops), as well as tillage methods that incorporate plant residue into the soil. Both of these techniques will help reduce BSR pathogen populations by promoting decomposition of soybean residue. Also, make sure that soil fertility and pH are optimized for soybean production to avoid overly low phosphorus and potassium levels, as well as overly low soil pH. Finally, grow soybean varieties with resistance to BSR. Complete resistance to BSR is not available in commercial varieties. However several sources of partial resistance that provide moderate to excellent BSR control are available. Also, some, but not all, varieties of soybean cyst nematode (SCN) resistant soybeans also are resistant to BSR. Most soybean varieties with SCN resistance derived from PI 88788 express resistance to BSR. However, the same is not true of varieties with SCN resistance derived from Peking. Therefore growers should consult seed company representatives about BSR resistance when selecting a variety with SCN resistance derived from this source.

For more information on brown stem rot of soybean:

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 Craig Grau, Bryan Jensen 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 agriculture-related questions at https://extension.wisc.edu/agriculture/ask-an-agriculture-question/.

Disease - Field and Forage

Brown Spot (Septoria Leaf Spot)

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Michelle Moyer and Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/28/2024

D-number: D0025

What is brown spot?

Brown spot of soybean, also referred to as Septoria leaf spot or Septoria brown spot, is a common and usually relatively minor foliar disease of soybean in Wisconsin. Brown spot typically does not lead to significant yield loss in soybeans produced in the state, although yield losses of up to 15% have been reported from other areas of the US. In Wisconsin, brown spot tends to be more prevalent on soybeans that are under stress [e.g., stress due to drought, low fertility (particularly low potassium), high insect feeding, or other diseases such as soybean cyst nematode].

Angular, reddish-brown leaf spots are typical of brown spot. (photo courtesy of Craig Grau)

What does brown spot look like?

The most typical symptom of brown spot is the formation of angular, reddish-brown spots (pinpoint to ¹/₈ inch in diameter) on both primary and trifoliolate soybean leaves. Small, roughly spherical pycnidia (reproductive structures) of the causal fungus (visible with a hand lens) form in the brown areas. The pycnidia often ooze strands or masses of tannish fungal spores. When brown spot is severe, plants may begin to defoliate from the ground up. The disease is often more prevalent where drainage is poor.

Where does brown spot come from?

Brown spot is caused by the fungus Septoria glycines, which survives in residue from previously diseased soybean crops. The fungus can also survive on diseased seeds. Brown spot tends to be more common during warm, wet weather, and when relative humidity is high.

How can I save a soybean crop with brown spot?

Brown spot is not a lethal disease, and in Wisconsin, it rarely leads to economic loss. However brown spot is more prevalent, and can be yield limiting, in late planted soybeans and in early maturing soybean varieties. Fungicide treatments for brown spot are typically neither warranted nor economical.

How can I avoid problems with brown spot in the future?

Brown spot is best managed through proper rotation. DO NOT grow soybeans continuously in the same field, but rotate soybeans with other crops for at least one year to allow time for soybean residues to naturally decay. Tillage techniques that bury crop residue and promote more rapid decay of residues that harbor the brown spot pathogen may also help provide control. Also, avoid using seed that has been produced in fields with high levels of the disease. Finally, reduce other stresses on your soybeans that may predispose plants to brown spot. Plants that are properly fertilized, have sufficient water and are insect- and pathogen-free are less likely to develop the disease.

For more information on brown spot of soybean:

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 Craig Grau, Bryan Jensen and Jim Stute 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 - Fruit Crop

Brown Rot

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Ashley Ellinghuysen*, UW-Madison Plant Pathology

Last Revised: 02/28/2024

D-number: D0024

What is brown rot?

Brown rot is a destructive fungal disease of trees and shrubs in the genus Prunus, which includes peaches, plum, cherries, apricots and nectarines. Brown rot is particularly a problem on the fruits of susceptible plants, with the potential to cause losses of 50% or more prior to harvest. After harvest, additional losses due to the disease are possible if fruits are injured, bruised or stored at warm temperatures with moisture.

The presence of powdery gray masses on the surface of rotting fruit is characteristic of brown rot. (Photo courtesy of Wayne Griffiths)

What does brown rot look like?

Initial symptoms of brown rot often occur in the spring as brown spots on blossoms. Affected blossoms eventually collapse completely, and can produce a gummy material that sticks to twigs leading to infections and subsequent twig dieback. Fruits that develop from healthy flowers can become infected as they mature leading to a brown fruit rot that quickly encompasses an entire fruit. Eventually, affected fruits will dry and shrivel to form “mummies”. Characteristic powdery, gray masses of spores form on the surfaces of both rotting fruits and mummies.

Where does brown rot come from?

Brown rot is caused by two fungi in the genus Monilinia (primarily M. fructicola and less commonly M. laxa). These fungi may be introduced into a garden via airborne spores produced on nearby wild or volunteer Prunus trees and shrubs. Insects such as sap beetles, vinegar flies and honeybees can also transport spores. These insects are attracted to brown rotted fruit and can subsequently visit and drop off spores on otherwise healthy fruit. Wounds due to insect feeding or hail can provide an entry point into fruits for brown rot fungi. Further spread can occur when infected and healthy fruits touch. Once introduced into a garden, brown rot fungi can overwinter on infected twigs and in mummified fruits that are hanging from trees or have fallen to the ground. Initial infections each spring are typically due to spores that are blown or splashed from twigs or from the gray masses on mummified fruits. More rarely, mummified fruits that are partially or shallowly buried in the ground will produce small (up to ¹/₁₆ inch diameter) mushroom-like structures called apothecia. Apothecia produce a second type of spore that can cause infections. Brown rot can occur under a wide range of temperatures (40 to 86°F), but tends to be more of a problem when the weather is warm (i.e., 68 to 77°F) and wet (i.e., with three or more hours of rain or dew formation).

How do I save a tree with brown rot?

Brown rot is not a lethal disease, but once fruits are infected, there are no curative treatments. To manage twig infections, prune four to six inches below sunken or dead tissue on each branch. Dispose of these branches by burning (where allowed by local ordinance) or burying them. To prevent spread of brown rot fungi on pruning tools, decontaminate tools between each cut by treating them for at least 30 seconds in a 10% bleach solution or preferably (due to its less corrosive properties) 70% alcohol. Rubbing alcohol and many spray disinfectants contain approximately 70% alcohol and are easy to use. If you use bleach, be sure to thoroughly rinse and oil tools after pruning to prevent rusting.

Fruits with brown rot eventually shrivel and dry forming a structure called a mummy. (Photo courtesy of Wayne Griffiths)

How do I avoid problems with brown rot in the future?

Remove and destroy any wild or volunteer Prunus trees and shrubs on your property, as well as all rotting and mummified Prunus fruits, as these can be reservoirs for brown rot fungi. Burn (where allowed by local ordinance) or deep bury these materials. Thin your Prunus trees to increase air flow and promote more rapid drying of twigs and fruits. For information on how and when to prune, see UW Bulletin A3629, Growing Apricots, Cherries, Peaches, and Plums in Wisconsin (available at https://learningstore.extension.wisc.edu/). Be sure to decontaminate cutting tools after tree/shrub removal and pruning as described above. Carefully handle fruits during harvest to minimize bruising, and store fruits in a cool, not overly wet environment.

If brown rot has been a chronic problem in your garden and the cultural methods discussed above have not proven successful for control, consider using fungicides. Select products that are labeled for use on apricots, cherries, peaches and/or plums and that contain captan, myclobutanil or propiconazole. To prevent blossom infections, make one application when approximately 10% of flowers are open. To prevent fruit infections, begin making applications three weeks before anticipated harvest, particularly if there is wet weather. When applying more than one application, DO NOT use myclobutanil and/or propiconazole for all treatments, as these active ingredients have similar modes of action; excessive use of these active ingredients can select for fungicide-resistant strains of brown rot fungi. Instead, alternate use of these active ingredients with use of captan or only use captan (which is not known to have problems with resistance development) for control. Also consider insecticide treatments to manage insects that can damage fruits and provide entry points for brown rot fungi. See UW Bulletin A4104, Midwest Fruit Pest Management Guide (available at https://learningstore.extension.wisc.edu/), for suggested insecticides and timings of applications. Be sure to read and follow all label instructions of any fungicides and insecticides that you select to ensure that you use these products in the safest and most effective manner possible. Be especially careful not to apply any pesticides closer to harvest than is allowed on the label.

For more information on brown rot:

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 558 at the University of Wisconsin Madison.

Thanks to Nolan Bornowski , Rebecca Ellinghuysen , Patty McManus , Patti Nagai, Scott Reuss and Brittany Seidl 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/.