All posts by hudelson

Disease - Vegetable

Potato Scab

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UW Plant Disease Facts

 

Authors:   Brian Hudelson, UW-Madison Plant Pathology
Last Revised:   03/01/2024
D-number:   D0083

What is potato scab? 

Potato scab is a common and disfiguring disease of potato tubers that affects potatoes wherever they are grown.  Thin-skinned potato varieties tend to be more severely affected.  This disease can also affect other root vegetables such as beets, carrots, parsnip, radish, rutabaga, salsify and turnip.

Sunken or raised, corky spots on potato tubers are characteristic of potato scab.
Sunken or raised, corky spots on potato tubers are characteristic of potato scab.

What does potato scab look like? 

Symptoms of scab are typically evident at harvest and vary widely depending upon potato variety and environmental conditions during tuber development.  Classic symptoms of scab include scab-like raised or slightly sunken rough, corky patches on tuber or root surfaces.  Under extreme conditions, large, deep pits may form.

Where does potato scab come from? 

Potato scab is caused by the bacterium Streptomyces scabies.  This bacterium is related to certain bacteria that produce antibiotics used to treat human diseases.  S. scabies occurs naturally in many soils, from soils with high organic matter content, to coarse and gravelly soils that tend to dry quickly.  S. scabies can also be introduced into garden soils when infected tubers are used as seed stock.

What do I do with potato tubers that have potato scab? 

Scabby potato tubers, while unsightly, are still edible.  Infected potatoes need only be peeled before use.  Store tubers with scab in a cool, dark, dry place to reduce the possibility of scabby areas becoming infected by soft rot bacteria that will totally decay tubers (see UW Plant Disease Facts D0010, Bacterial Soft Rot).

How do I avoid problems with potato scab in the future?  

Use certified, scab-free seed potatoes in your garden.  DO NOT use infected tubers to produce seed pieces.  Select potatoes varieties such as Norland, Russet Burbank and Superior that have at least moderate resistance to scab.  Try not to plant potatoes in the same spot in your garden more frequently than once every three years.  Rotate potatoes with crops such as corn, peas, and beans that are not susceptible to scab.  Scab tends not to develop when the soil pH is less than 5.2.  Therefore, acidify garden soils (i.e., make sure the soil pH is less than 7) where possible.  For home gardens, keeping the soil pH at approximately 6.5 is a good compromise when growing not only potatoes, but other vegetable crops.  Avoid using fertilizers (e.g., lime, calcium and potassium nitrate, or fresh manure) that may increase soil pH.  Finally, make sure to adequately water your potatoes, particularly as tubers are forming.

For more information on potato scab: 

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:

© 2003-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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 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.qa.webhosting.cals.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, Pest Alerts

Plum Pox – Pest Alert

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UW Plant Disease Facts

 

Pest Alert
Authors:   Emma Nelson and Leslie Holland, UW-Madison Department of Plant Pathology
Last Revised:   03/01/2024
D-number:   D0082

What is plum pox? 

Plum pox, also known as “sharka,” is one of the most devastating diseases of stone fruits (plums, peaches, nectarines, and apricots) worldwide.  This viral disease was first discovered on plums in Bulgaria in 1915 and subsequently has been observed in many parts of the world.  There are several variants of plum pox, but only one has been found in the United States.  This variant was first found in peach orchards in Pennsylvania in 1999 (the first report of plum pox in North America).  In 2006, the same variant was identified in Michigan and New York.  Primary hosts of the U.S. plum pox variant are peach, plum, and ornamental Prunus species.  Cherries and almonds are not considered natural hosts of this variant, but they can be artificially infected.  Other plum pox hosts include garden plants (e.g., tomatoes, peas, petunias, zinnias) and weeds (e.g., white clover, lamb’s quarters).  While plum pox does not kill stone fruit trees, it causes serious crop losses by making fruit deformed, discolored, tasteless, and unmarketable.  In 2019, after intense quarantine and destruction of infected trees and orchards, the United States Department of Agriculture declared that plum pox had been eradicated from the United States.

Plum pox symptoms on immature plum fruits (left), and a plum leaf (right). (Photographs courtesy of R. Scorza and obtained from West Virginia University at http://www.caf.wvu.edu/kearneysville/wvufarm1.html)
Plum pox symptoms on immature plum fruits (left), and a plum leaf (right). (Photographs courtesy of R. Scorza and obtained from West Virginia University at http://www.caf.wvu.edu/kearneysville/wvufarm1.html)

What does plum pox look like?  

Plum pox symptoms vary widely depending on host plant, plant age, plant nutrient status, environmental conditions, plum pox variant, and timing of infection.  Some infected plants do not exhibit any visible symptoms or may not develop symptoms until years after infection, making plum pox difficult to detect.  Additionally, symptoms may not be visible throughout an entire plant but limited to only a portion of the plant.  Once a plant starts to show symptoms however, it will continue to do so in subsequent years.  Of the stone fruits, plums are generally most severely affected by plum pox and show the most obvious symptoms.  Branches on infected trees may develop spots.  Leaves may develop yellow-green spots or blotches and mild, light-green discoloration near leaf veins (see photo above) that can be difficult to distinguish from other causes (e.g., nutrient deficiencies).  On peach trees, leaf crinkling, puckering, and curling may also occur.  Fruits may develop yellow rings or line patterns and become brown or necrotic (see photo above).  As fruits ripen, symptoms fade, but fruits drop from the tree prematurely.  Seeds may have white rings or line patterns.

Where does plum pox come from?  

Plum Pox is caused by the Plum pox virus (PPV).  PPV-D (one of six PPV variants/strains) is the only strain that has been detected in the United States.   PPV can be moved long distances via infected nursery stock such as infected trees or budwood used for grafting.  Once introduced into an orchard, the virus is spread short distances by aphids.  Aphid transmission occurs more frequently in spring and autumn.  PPV can overwinter in various parts of a tree, including the roots.

How do I save a tree with plum pox?  

Once a tree has been infected with PPV, it cannot be cured.  Timely and complete eradication of infected trees and even entire orchards is the only effective way to prevent further spread.  Diseased trees (including stumps) should be removed and destroyed (i.e., burned and/or buried).  Trees surrounding a problematic area should be monitored frequently for symptom development.  Other potential host plants (see above) should also be monitored for symptoms of disease.  If you see what you believe to be plum pox symptoms, contact your local plant disease diagnostic clinic immediately (see http://npdn.org/ for the lab nearest you).  In Wisconsin, contact the UW-Madison Plant Disease Diagnostics Clinic (PDDC) at (608) 262-283 or pddc@wisc.edu.  PPV is a federally regulated pathogen and if detected, infected plants must be destroyed to prevent further spread.  For more information on the federal regulation of PPV, see https://www.aphis.usda.gov/aphis/ourfocus/planthealth/plant-pest-and-disease-programs/pests-and-diseases/. 

How do I avoid problems with plum pox in the future?  

After 20 years and elimination of over 1,500 acres of fruit trees, PPV has been eradicated in the United States.  Preventing reintroduction of the PPV in the United States is critical.  To prevent reintroduction of PPV, only use nursery stock that is certified virus-free.  Also consider planting resistant varieties, but keep in mind that existing resistant varieties can still carry the virus and be asymptomatic.  Additional control strategies for plum pox include managing aphids that can transmit PPV, following quarantine regulations, and routinely scouting and surveying orchards for plum pox and PPV.  Ongoing monitoring for plum pox in stone-fruit-producing states and regulating imported trees will help ensure that the United States remains free of PPV.

For more information on plum pox: 

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:

© 2021-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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 Patty Meister, Josie Russo and Carol Shirk 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.qa.webhosting.cals.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

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

What is Phytophthora root rot? 

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

What does Phytophthora root rot look like?  

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

Where does Phytophthora root rot come from? 

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

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

How do I save a plant with Phytophthora root rot? 

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

How do I avoid problems with Phytophthora root rot in the future?  

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

For more information on Phytophthora root rot of Christmas trees: 

Contact 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:

© 2015-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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

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

Thanks to Bryan Jensen, 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.qa.webhosting.cals.wisc.edu.

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

Disease - Field and Forage

Phytophthora Root and Stem Rot of Soybean

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UW Plant Disease Facts

 

Authors:   Carol Groves and Damon Smith, UW-Madison Plant Pathology
Last Revised:   03/01/2024
D-number:   D0078

What is Phytophthora root and stem rot? 

Phytophthora root and stem rot (PRSR) is a common disease of soybean that can ultimately cause death of soybeans at any stage of development.  The disease can cause stand losses and severe yield reductions in susceptible soybean varieties.  In Wisconsin, PRSR of soybean is becoming increasingly important due to expansion of soybean acreage, increased frequency of planting of soybeans in given fields, and substantial variability in the organism that causes the disease.

Post-emergence damping-off of soybean seedlings due to Phytophthora root and stem rot. (photo courtesy of Craig Grau)
Post-emergence damping-off of soybean seedlings due to Phytophthora root and stem rot. (photo courtesy of Craig Grau)

What does What does Phytophthora root and stem rot look like? 

Watch for symptoms of PRSR in fields or areas of fields with poor drainage (e.g., low-lying areas or areas with soil compaction problems).  In addition, watch for the disease in well-drained fields when soils are saturated due to heavy rain or excessive irrigation.  Symptomatic plants often occur in patches.

Symptoms of PRSR can vary depending on the age of affected plants.  Early stages of PRSR can lead to seed rot or death of seedlings prior to emergence (called pre-emergence damping-off).  Once plants emerge, PRSR can lead to yellowing, wilting, and death of seedlings (called post-emergence damping-off).  Infected seedlings can be pulled easily from the ground because of damage to developing roots.  Symptoms of PRSR in older plants (particularly those infected before flowering) include root decay, browning and water-soaking of stems extending six to 12 inches above the soil line, yellowing of leaves, wilting, and eventual death, with leaves on dead plants remaining attached.  Stem lesions of PRSR are typically brown, long, narrow, and sunken.  When infections remain confined primarily in roots, above-ground symptoms may be more subtle, and can include a lighter green color, stunting and uneven growth.  Death due to PRSR tends to occur more rapidly in younger plants than older plants.

Symptoms of PRSR can be similar to symptoms of other soybean diseases, particularly Pythium root rot (PRR) and stem canker.  PRR causes root symptoms similar to those caused by PRSR but typically not the expansive stem lesions seen with PRSR.  Stem canker, like PRSR, causes stem lesions, but stem canker lesions tend to be larger (eventually girdling stems), and become darker brown with age than those caused by PRSR.  Also, older stem canker lesions will have numerous black, pimple-like spots (actually reproductive structures of the fungus that causes the disease).  Such spots will not be present in lesions of plants suffering from PRSR.

Where does Phytophthora root and stem rot come from? 

PRSR is caused by the water mold Phytophthora sojae, a soilborne organism that survives via specialized, thick-walled spores called oospores.  Oospores are produced in infected soybean plants, and can survive for many years in the soil after soybean residues decompose.  Oospores germinate when soil moisture is high.  P. sojae tends to be most active when temperatures are between 58 and 77°F, in contrast to Pythium species (the causes of Pythium root rot), which tend to be active over a wider temperature range (50 to 95°F).

How can I save a soybean crop with Phytophthora root and stem rot? 

Once soybean plants become infected by P. sojae, there is no cure.  Therefore, management of PRSR relies on preventing infections from occurring.

Brown stem discoloration and plant death (with leaves remaining attached) is typical of Phytophthora root and stem rot. (photo courtesy of Craig Grau)
Brown stem discoloration and plant death (with leaves remaining attached) is typical of Phytophthora root and stem rot. (photo courtesy of Craig Grau)

How can I avoid problems with Phytophthora root and stem rot in the future?  

Use PRSR-resistant varieties as a primary means of disease management.  Both race-specific resistance [complete resistance to a specific variant of the pathogen (called a race)] and field resistance (partial resistance to many races) are available in soybean varieties marketed in Wisconsin.  When choosing a race-specific variety, be sure to know which race(s) of the pathogen is/are prevalent in your area and match race-specific resistance genes with the predominant race(s).  The performance of race-specific resistant varieties can change over time.  Therefore, monitor the performance of race-specific resistant varieties very closely, and base future selection of race-specific resistant varieties on the performance (or lack thereof) of recently planted varieties.  Field (partial) resistance to PRSR is present at differing levels in most soybean varieties marketed in Wisconsin.  While field resistance can be useful in managing PRSR, this type of resistance is not particularly effective during early growth stages or under high disease pressure (e.g., when P. sojae levels are high in soil or when soil conditions are excessively wet).  In addition to using resistant varieties, consider using seed treatments containing metalaxyl or mefenoxam.  These active ingredients have been shown to be effective in providing early protection of soybean seeds and seedlings against P. sojae.  Also, improve soil drainage to promote drier soils that are less favorable for P. sojae growth and reproduction.  Crop rotation will not eliminate PRSR or eradicate P. sojae but should be used to prevent the rapid build-up of high levels of the pathogen that can reduce the effectiveness of field resistance.

For more information on Phytophthora root and 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:

© 2013-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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 Craig Grau, Bryan Jensen and Chris Williamson 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.qa.webhosting.cals.wisc.edu.

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

Disease - Needled Woody Ornamental

Phomopsis Tip Blight

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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.
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:

*Completed as partial fulfillment of the requirements for Plant Pathology 875 – Plant Disease Diagnostics Clinic Internship at the University of Wisconsin Madison.

© 2002-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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 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.qa.webhosting.cals.wisc.edu.

 

Disease - Broad Leafed Woody Ornamental

Oak Wilt

Extension Logo

UW Plant Disease Facts

 

Authors:   Jim Olis* and Brian Hudelson, UW-Madison Plant Pathology
Last Revised:   03/20/2024
D-number:   D0075

What is oak wilt? 

Oak wilt is a lethal fungal disease that affects virtually all species of oaks.  Oaks in the red oak group (oaks with pointed leaf lobes) such as red, scarlet, black and Northern pin oak are most susceptible.  Oaks in the white oak group (those with rounded leaf lobes) such as white, bur, post, and swamp white oak are less susceptible.

What does oak wilt look like? 

Initially, single branches on infected trees wilt and die.  Leaves on these branches often bronze, or turn tan or dull green, starting at the tips or outer margins.  Leaves may also droop, curl, or fall from the tree.  Infected trees eventually die.  Oak wilt can kill oaks in the red oak group in less than one month.  Oaks in the white oak group usually have less severe symptoms and rarely die in a single season.

Marginal leaf bronzing or tanning is often an early symptom of oak wilt.
Marginal leaf bronzing or tanning is often an early symptom of oak wilt.

Where does oak wilt come from? 

Oak wilt is caused by the fungus Bretziella fagacearum, which survives in infected living oaks and in oaks recently killed by the disease.  The fungus can also survive in firewood harvested from an infected tree. 

Sap beetles are attracted to mats of the oak wilt fungus in infected trees, pick up spores of the fungus on their bodies, then carry spores to healthy trees.  These beetles are attracted to trees that have been recently wounded by wind or storm damage, or by pruning.  Oak bark beetles such as Pseudopityophthorus minutissimus and Pseudopityophthorus pruinosus are also known to move the oak wilt fungus from tree to tree.  In particular, Pseudopityophthorus minutissimus has been observed more frequently in Wisconsin in recent years.  The relative importance of sap beetles vs. oak bark beetles in the transmission of the oak wilt fungus in Wisconsin is not known at this time. 

Once Bretziella fagacearum has infected an oak tree, natural grafts between roots of oak trees growing near each other serve as a means by which the fungus moves from tree to tree.  Root grafts most commonly form between oak trees in the same oak group (see above for details), but root grafts between red oak group and white oak group oaks can also occur on occasion. 

How do I save a tree with oak wilt? 

Removing infected oaks is often the best way to manage oak wilt.  Before removing trees, be sure to disrupt root grafts between infected and other nearby oaks.  This will help limit tree to tree movement of the fungus during the removal process.  Burn or bury wood from diseased oaks, if possible.  If you decide to keep the wood, remove the bark, pile it in one place and cover it with a heavy tarp, burying the tarp edges with soil until you use it.  This will limit sap or bark beetle access to the pile and reduce the risk that these insects will acquire the oak wilt fungus.  Propiconazole injections can be used for oak wilt management, but these treatments work best when used before, rather than after, oak trees are infected.

How do I avoid problems with oak wilt in the future?  

Prune oak trees only during the dormant season when sap and bark beetles are not active.  If you must prune during the growing season (e.g., due to storm damage) IMMEDIATELY cover wounds with paint.  Sap beetles can visit wounded oaks within 10 minutes of wound formation.  Monitor oaks for oak wilt and remove infected trees promptly. 

For more information on oak wilt: 

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:

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

© 2001-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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 Ann Joy, Laura Jull 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.qa.webhosting.cals.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

Nectria Canker

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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.
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:

© 2002-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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 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.qa.webhosting.cals.wisc.edu.

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

Turf

Microdochium Patch

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UW Plant Disease Facts

 

Authors:   Sarah Rosenthal*, UW-Plant Breeding and Plant Genetics and Geunhwa Jung, formerly of UW-Plant Pathology
Last Revised:   03/01/2024
D-number:   D0073

What is Microdochium patch? 

Microdochium patch, also known as pink snow mold, is a fungal disease affecting cool season grasses such as annual, Kentucky, and rough bluegrass; colonial, velvet, and creeping bentgrass; perennial ryegrass; and fine and tall fescue.  These grasses are used in the majority of home lawns and golf courses in the Midwest.

On short-cut grass, Microdochium patch leads to the formation of round, pink-edged patches of dead turf that form over the winter.
On short-cut grass, Microdochium patch leads to the formation of round, pink-edged patches of dead turf that form over the winter.

What does Microdochium patch look like? 

Microdochium patch is characterized by the formation of circular patches of dead turf.  The dead areas can range in size from a few inches to a few feet in diameter.  When Microdochium patch develops on short-cut turf under a layer of snow, distinct dead patches appear that are bleached and matted.  When the disease develops on short-cut turf in the absence of snow, dead patches appear reddish-brown.  White fungal threads (called a mycelium) typically develop in the center of the patches, with pinkish-red threads forming at the borders.  On taller grass (greater than six inches), yellow blighted patches with diffuse margins can form.

Where does Microdochium patch come from? 

Microdochium patch is caused by the fungus Microdochium nivale which survives as fungal threads or spores in infested plant debris.  The fungus begins to grow under the snow during the winter and continues to grow until the turf warms and dries in the spring.  In addition, Microdochium patch can be found during damp, cool spring and fall weather.  The disease is more severe under cool (30 to 60°F), wet conditions, in alkaline soils, and when high levels of nitrogen fertilizer are applied early (or extremely late) in the growing season.

How do I save turf with Microdochium patch? 

Turf with Microdochium patch will often recover, but severely affected areas will need to be reseeded or replaced with Microdochium patch-resistant turf.  The least susceptible grass species are Kentucky bluegrass and fine fescue.

On taller grass, Microdochium patch can lead to a diffuse, yellow blighting of the turf.
On taller grass, Microdochium patch can lead to a diffuse, yellow blighting of the turf.

How do I avoid problems with Microdochium patch in the future? 

When establishing a lawn, make sure that soils are well-drained and do not accumulate excessive amounts of water.  Make sure that the soil pH is 7.0 or below, and also be sure to plant a Microdocium patch resistant grass variety (e.g., Kentucky bluegrass or fine fescue).  In established lawns, DO NOT apply fast releasing nitrogen fertilizers (e.g., urea or ammonium nitrate) in the fall, and continue to mow grass until it goes dormant.  Maintain a soil pH of 7.0 or below.  Remove thatch in your lawn in either September or May, if the thatch layer is greater than 1/2 inch.  Building a snow fence to minimize snow accumulation, and encouraging rapid snow melting may also help reduce the incidence and severity of Microdochium patch.  Fungicides containing the active ingredients azoxystrobin, chlorothalonil, fenarimol, fludioxonil, iprodione, mancozeb, myclobutanil, PCNB, polyoxin D, propiconazole, pyraclostrobin, thiophanate-methyl, thiram, triadimefon, trifloxystrobin, and vinclozolin are labeled for Microdochium patch control, and can be applied in October or November to prevent disease in the spring.  However, these treatments are often not cost-effective.  If you decide to use fungicides for control, be sure to read and follow all label instructions of the fungicide that you select to ensure that you use the product in the safest and most effective manner possible.

For more information on Microdochium patch: 

Contact the University of Wisconsin Turf Diagnostic Lab (TDL) at (608) 845-2535 or hockemeyer@wisc.edu.

This Fact Sheet is also available in PDF format:

*Completed as partial fulfillment of the requirements for Plant Pathology 559 – Diseases of Economic Plants at the University of Wisconsin Madison.

© 2007-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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 Jason Dettman-Kruse, Bruce Schweiger and John Stier 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.qa.webhosting.cals.wisc.edu.

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

Uncategorized

Lichens

There are many types of lichens. Crustose lichens (left) are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens (right) are leaf-like and composed of flat sheets of tissue that are not tightly bound.
There are many types of lichens. Crustose lichens (left) are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens (right) are leaf-like and composed of flat sheets of tissue that are not tightly bound.

There are many types of lichens. Crustose lichens (left) are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens (right) are leaf-like and composed of flat sheets of tissue that are not tightly bound.What are lichens?  Lichens are organisms that arise from mutually beneficial interactions between certain filamentous fungi, algae and yeasts.  The filamentous fungi provide the physical structures of the lichens, as well as protection for the algae and yeasts.  The algae produce food for the fungi and yeasts via photosynthesis.  The yeasts are thought to produce compounds to fend off disease-causing organisms and insect pests.

What do lichens look like?  Lichens come in four basic growth forms.  Crustose lichens are crust-like and adhere tightly to the surface upon which they grow.  Foliose lichens are leaf-like and composed of flat sheets of tissue that are not tightly bound together.  Squamulose lichens are composed of scale-like parts.  Fruticose lichens are composed of free-standing branching tubes.

Where do lichens come from?  Lichens are everywhere.  There are an estimated 13,500 to 17,000 species of lichens, and lichens can be found growing in tropical, temperate and polar regions throughout the world.  Lichens will grow on almost any surface that is stable and reasonably well-lit.  In temperate regions, lichens can often be found growing on the bark of trees or old fence posts.  Others lichens grow in less hospitable places, such as bare rock surfaces or old headstones in graveyards, where they aid in the breakdown of rocks and the formation of soil.

There are many types of lichens. Crustose lichens (left) are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens (right) are leaf-like and composed of flat sheets of tissue that are not tightly bound.
There are many types of lichens. Crustose lichens (left) are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens (right) are leaf-like and composed of flat sheets of tissue that are not tightly bound.

How do I save a tree with lichens?  DO NOT PANIC!  Lichens do not harm trees; they are not pathogens or parasites, and do not cause disease.  Lichens are self-reliant, with the algal component of the lichen producing food for the organism via photosynthesis.  Lichens absorb water and minerals from rainwater and the atmosphere, and because of this, they are extremely sensitive to air pollution.  As a result, the presence or absence of certain lichen species can be used as an indicator of levels of atmospheric pollutants.  Information on the abundance and species of lichens growing in an area can give a good indication of the local air quality.

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

Disease - Field and Forage

Leaf and Glume Blotch of Small Grains

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UW Plant Disease Facts

 

Authors:   Damon Smith, UW-Madison Plant Pathology
Last Revised:   03/01/2024
D-number:   D0070

What is leaf and glume blotch? 

Leaf and glume blotch is a common disease of wheat, and to a lesser extent barley and rye.  While the impact of the disease is typically relatively minor (usually 5% or less of a wheat crop is affected), under favorable environmental conditions, leaf and glume blotch can destroy upwards of 20% of a wheat crop.

Blotchy brown to purple discolorations on grain heads are characteristic of leaf and glume blotch of wheat. Photo courtesy of Craig Grau.
Blotchy brown to purple discolorations on grain heads are characteristic of leaf and glume blotch of wheat. Photo courtesy of Craig Grau.

What does leaf and glume blotch look like? 

Leaf and glume blotch on leaves appears initially as small yellow flecks that enlarge to form brown, lens-shaped lesions, often surrounded by yellow halos.  These regions can merge, leading to large necrotic (i.e., dead) areas on leaves.  The disease can also affect stems and grain heads resulting in smaller brown to purple lesions on tillers and botchy brown to purple areas on glumes (i.e., the leafy, husk tissue that surrounds developing seeds).  As the disease develops, small, dark, pimple-like dots (reproductive structures of the fungus that causes the disease) form in the discolored tissue.  When the humidity is high, gelatinous masses of fungal spores are exuded from these tiny dots giving leaves, stems and grain heads a shiny, wet appearance.

Where does leaf and glume blotch come from? 

Leaf and glume blotch is caused by the fungus Parastagonospora nodorum which can survive in wheat debris, as well as in wheat seed.  Spores of the fungus are produced on wheat debris and on infected plants during periods of high humidity and moderate temperatures (optimally around 68°F) and are easily moved within a wheat planting by splashing due to heavy rains.

How can I save plants with leaf and glume blotch? 

Once plants are infected with the leaf and glume blotch fungus, curative treatments are not available.  Luckily, under weather conditions typical for small grain production in Wisconsin, damage due to leaf and glume blotch is not severe (at most perhaps 5% of an overall wheat crop in a typical growing season).  However, under weather conditions favorable for leaf and glume blotch to develop, early detection of the disease is important to provide greater flexibility in applying fungicide treatments that can limit disease development (see details below).  In particular, fungicide treatments that protect the flag leaves of wheat plants (i.e., the leaves just under the grain heads) can be important in preventing significant losses due to leaf and glume blotch.

On wheat leaves, leaf and glume blotch leads to brown, lens-shaped lesions with yellow halos. Photo courtesy of Craig Grau.
On wheat leaves, leaf and glume blotch leads to brown, lens-shaped lesions with yellow halos. Photo courtesy of Craig Grau.

How can I avoid problems with leaf and glume blotch in the future? 

The best method for managing leaf and glume blotch is through the use of appropriate crop rotation.  Rotate wheat and other small grains with nonsusceptible crops (e.g., soybeans, corn, or vegetable crops) for at least one year.  Where feasible, also consider using tillage practices that partially or fully bury wheat debris, and avoid planting wheat excessively early.  Rotation, proper tillage and delayed planting all provide time for wheat debris to decay, which in turn eliminates the primary source of spores of the leaf and glume blotch fungus.  Also, use wheat seed that was produced in leaf and glume blotch-free fields to avoid introducing the fungus on contaminated seed.

Where leaf and glume blotch has been a chronic problem, use leaf and glume blotch-resistant wheat cultivars and reduce seeding rates to allow better air penetration and more rapid drying of plants.  Avoid overuse of nitrogen fertilizers as this will promote excessive leaf growth that will slow leaf drying.  Finally, scout wheat fields routinely, and consider using preventative fungicide treatments at the emerging flag leaf stage of development (Feekes 8).  Many strobilurin fungicides (FRAC group 11) and demethylation inhibitor fungicides (FRAC group 3), as well as mixes of active ingredients with these modes of action, provide very good control of leaf and glume blotch.  Use fungicides containing a strobilurin only prior to heading; avoid using these products after wheat has flowered.  Demythylation inhibitor fungicides can be applied both before and after wheat has flowered.  Be sure to read and follow all label instructions of the fungicide(s) that you select to ensure that you use the material(s) in the safest and most effective manner possible.

For more information on leaf and glume blotch:  

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:

© 2015-2024 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.

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 Nick Baker, Bryan Jensen and George Koepp 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.qa.webhosting.cals.wisc.edu.

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