All posts by hudelson

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

Downy Mildew

July 21, 2015 hudelson

UW Plant Disease Facts

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

Last Revised: 02/29/2024

D-number: D0044

What is downy mildew?

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

What does downy mildew look like?

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

Where does downy mildew come from?

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

How do I save a plant with downy mildew?

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

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

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

For more information on downy mildew:

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

This Fact Sheet is also available in PDF format:

Full Color PDF

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

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

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

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

Disease - Needled Woody Ornamental

Dothistroma Needle Blight

July 21, 2015 hudelson

UW Plant Disease Facts

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

Last Revised: 02/29/2024

D-number: D0043

What is Dothistroma needle blight?

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

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

What does Dothistroma needle blight look like?

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

Where does Dothistroma needle blight come from?

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

How do I save a tree with Dothistroma needle blight?

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

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

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

For more information on Dothistroma needle blight:

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

This Fact Sheet is also available in PDF format:

Full Color PDF

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

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

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

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

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

Dodder

July 21, 2015 hudelson

UW Plant Disease Facts

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

Last Revised: 02/29/2024

D-number: D0129

Spaghetti-like dodder plants parasitizing carrots.

What is dodder?

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

What does dodder look like?

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

Where does dodder come from?

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

How do I save plants parasitized by dodder?

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

How do I avoid problems with dodder in the future?

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

For more information on dodder:

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

This Fact Sheet is also available in PDF format:

Full Color PDF

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

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

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

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

Dead Man’s Fingers

July 19, 2015 hudelson

UW Plant Disease Facts

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

Last Revised: 02/29/2024

D-number: D0040

What is dead man’s fingers?

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

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

What does dead man’s fingers look like?

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

Where does dead man’s fingers come from?

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

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

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

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

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

For more information on dead man’s fingers:

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

This Fact Sheet is also available in PDF format:

Full Color PDF

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

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

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

Disease - Herbaceous Ornamental

Daylily Leaf Streak

July 19, 2015 hudelson

UW Plant Disease Facts

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

Last Revised: 02/29/2024

D-number: D0039

What is leaf streak?

Leaf streak is a common disease of daylilies, affecting daylilies wherever they are grown. Daylily varieties can vary widely in terms of their susceptibility to the disease. Oftentimes leaf streak is a cosmetic problem, causing little damage. In some cases however, leaf streak can cause substantial leaf loss, and rarely, it may lead to complete defoliation of daylily plants.

Yellowing and browning of leaves typical of daylily leaf streak. (Photo courtesy of Doug Maxwell)

What does leaf streak look like?

Leaf streak symptoms often initially appear as yellowing that begins at leaf tips and spreads down along and outward from the midveins of leaves. This tissue eventually browns and dies. Red-brown flecks may also be a symptom of leaf streak. These flecks enlarge, turn brown and become surrounded by yellow halos. As the disease progresses, complete leaf death can occur.

Where does leaf streak come from?

Leaf streak is caused by the fungus Aureobasidium microstictum. This fungus overwinters in daylily leaf debris where it produces spores that initiate the disease each spring. Spores produced on infected leaves lead to additional infections. The disease is most common in warm, wet weather.

How do I save a plant with leaf streak?

Remove infected leaves as they appear, and fertilize and water your plants properly to promote growth of new leaves. DO NOT water with a sprinkler. This can spread the leaf streak fungus, as well create conditions more favorable for infection. Instead, use a soaker or drip hose to apply water directly into the soil. To further limit pathogen spread, avoid working with plants when they are wet.

How do I avoid problems with leaf streak in the future?

Remove dead leaves from daylilies each fall to eliminate a source of the leaf streak fungus. Burn (where allowed by local ordinance), deep bury or hot compost this material. As daylily plants grow, divide them into smaller clumps, and replant them with ample space between clumps. This will improve air circulation and promote more rapid leaf drying. Consider using daylily varieties (e.g., ‘Betty Bennet’, ‘Edna Spalding’, ‘Ella Pettigrew’, ‘Globe Trotter’, ‘Nancy Hicks’, ‘Pink Superior’, ‘Ron Rousseau’, ‘Sudie’, ‘Tropical Tones’, ‘Upper Room’, ‘Winsome Lady’) with reported leaf streak resistance. Keep in mind however, that resistant varieties may not perform well every year and under all environmental conditions. If you grow daylily varieties that have severe leaf streak every year, consider applying fungicides containing chlorothalonil, mancozeb or thiophanate-methyl to prevent the disease. Use fungicides only during periods of wet weather. Start applications before you see symptoms and treat every seven to 14 days as long as wet weather persists. DO NOT use the same active ingredient for all treatments, particularly if you decide to use thiophanate-methyl. Alternate use of at least two active ingredients to help minimize problems with fungicide-resistant strains of the leaf streak pathogen. 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.

For more information on daylily leaf streak:

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

This Fact Sheet is also available in PDF format:

Full Color PDF

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

Thanks to Heidi Doering, Doug Maxwell 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 - Herbaceous Ornamental, Disease - Vegetable

Damping-Off

July 19, 2015 hudelson

UW Plant Disease Facts

Authors: Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/29/2024

D-number: D0038

What is damping-off?

Damping-off is a common and fatal disease that affects all types of plant seedlings. The disease is most prevalent when seeds are germinated in cool, wet soils. Fortunately, seedlings are susceptible to damping-off for only a short period following emergence. As plants age, their susceptibility to damping-off declines.

Lower stem collapse of Zinnia seedlings due to damping-off.

What does damping-off look like?

Seedlings killed by damping-off initially are healthy but shortly after emergence become infected at or just below the soil line. The lower stems of the seedlings collapse, and the seedlings fall over onto the soil surface. The seedlings subsequently die.

Where does damping-off come from?

Damping-off is caused by several soil-borne water molds and fungi, including (but not limited to) Pythium spp., Rhizoctonia solani and Fusarium spp. These organisms readily survive and are moved in soil or on soil-contaminated items such as pots, tools and workbenches.

How do I save seedlings with damping-off?

Seedlings with damping-off will die and cannot be saved. Proper prevention is the only way to avoid problems with this disease.

How do I avoid problems with damping-off in the future?

When planting seeds, make sure that work areas, tools and pots are pathogen-free. Decontaminate tools and workbenches by treating them for at least 30 seconds with 10% bleach or (preferably due to its less corrosive properties) 70% alcohol (e.g., rubbing alcohol or certain spray disinfectants). Decontaminate pots by washing them with soapy water to remove bits of old soil, soaking them for at least 20 minutes in 10% bleach, and then rinsing them thoroughly to remove bleach residues. DO NOT reuse plastic pots if you have had problems with damping-off or root rots (see UW Plant Disease Facts D0095, Root Rots in the Garden, for details) in the past, as they are difficult to decontaminate.

When planting, use a well-drained, pasteurized potting mixture. DO NOT use garden soils as they often contain damping-off pathogens. DO NOT plant seeds too deeply, and germinate seeds at high temperatures, so that seedlings rapidly grow out of the stage where they are susceptible to damping-off. DO NOT overwater as damping-off organisms are more active in wet soils. If the techniques described above do not work, then consider using fungicide-treated seed. In particular, plants grown from captan-treated seeds tend to have fewer problems with damping-off.

For more information on damping-off:

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

This Fact Sheet is also available in PDF format:

Full Color PDF

Thanks to Lis Friemoth, Ann Joy 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 - Needled Woody Ornamental

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

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

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/.