All posts by hudelson

Disease - Vegetable

Septoria Leaf Spot

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UW Plant Disease Facts

 

Authors:   Brian Hudelson, UW-Madison Plant Pathology
Last Revised:   03/01/2024
D-number:   D0100

What is Septoria leaf spot? 

Septoria leaf spot is one of two common fungal diseases that can devastate tomatoes in both commercial settings and home gardens.  The second common tomato blight, early blight, is detailed in UW Plant Disease Facts D0046, Early Blight.

Septoria leaf spot. Note whitish spots with dark borders characteristic of the disease.
Septoria leaf spot. Note whitish spots with dark borders characteristic of the disease.

What does Septoria leaf spot look like? 

Symptoms of Septoria leaf spot first appear at the base of affected plants, where small (approximately ¼ inch diameter) spots appear on leaves and stems.  These spots typically have a whitish center and a dark border.  Eventually multiple spots on a single leaf will merge, leading to extensive destruction of leaf tissue.  Septoria leaf spot can lead to total defoliation of lower leaves and even the death of an infected plant.

Where does Septoria leaf spot come from? 

Septoria leaf spot is caused by the fungus Septoria lycopersici, which survives in plant debris or on infected plants.  Septoria leaf spot symptoms typically begin as plant canopies start to close.  Denser foliage leads to high humidity and longer periods of leaf wetness that favor the disease.

How do I save a plant with Septoria leaf spot? 

Once symptoms of Septoria leaf spot appear, control is difficult.  Thinning of whole plants or removal of selected branches from individual plants may slow the disease by increasing airflow and thus reducing humidity and the length of time that leaves remain wet.  Fungicides labeled for use on vegetables and containing copper or chlorothalonil may also provide control of Septoria leaf spot if they are carefully applied very early in the course of the disease (before symptoms develop is best) and on a regular basis throughout the rest of the growing season.  If you decide to use fungicides for disease 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 Septoria leaf spot in the future?  

Septoria leaf spot is best controlled using preventative measures.  Destroy infested plants by burning (where allowed by local ordinance) or burying them.  Rotate vegetables to different parts of your garden each year to avoid areas where infested debris (and thus spores of Septoria lycopersici) may be present.  See University of Wisconsin Garden Facts XHT1210, Using Crop Rotation in the Home Vegetable Garden, for details on this technique.  Use Septoria leaf spot-resistant tomato varieties whenever possible.  Increase spacing between plants to increase airflow and decrease humidity and foliage drying time.  Mulch your garden with approximately one inch of a high quality mulch, but DO NOT overmulch as this can lead to wet soils that can contribute to increased humidity.  Finally, where the disease has been a chronic problem, use of preventative applications of a copper or chlorothalonil-containing fungicide labeled for use on vegetables may be warranted.

For more information on Septoria leaf spot: 

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:

© 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 Karen Delahaut, Lisa Johnson and Ann Joy for reviewing this document.

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

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

Disease - Field and Forage

Sclerotinia Stem Rot of Soybean

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UW Plant Disease Facts

 

Authors:   Quinn Watson and Damon Smith, UW-Madison Plant Pathology
Last Revised:   03/01/2024
D-number:   D0099

What is Sclerotinia stem rot? 

Sclerotinia stem rot (SSR), also known as white mold, is a serious and often lethal fungal disease that affects a wide range of agricultural crops in the United States including many broadleaf vegetable crops (e.g., carrots, cruciferous plants, peas, potatoes, snap beans) and field crops, especially soybean.  SSR is most severe on soybeans in high-yielding environments that have dense, fast-growing canopies.

Cottony white growth of the Sclerotinia stem rot fungus on a soybean plant.
Cottony white growth of the Sclerotinia stem rot fungus on a soybean plant.

What does Sclerotinia stem rot look like? 

SSR causes sudden wilting of soybean leaves and rapid plant death.  Lower stems of affected plants become bleached and under moist conditions (e.g., high humidity, frequent rain), become covered with a cottony white fungal growth.  Small, black structures that look like rat or mouse droppings (called sclerotia) form on and inside the stems and pods of affected plants.

Where does Sclerotinia stem rot come from? 

Sclerotinia stem rot is caused by the fungus Sclerotinia sclerotiorum, which survives as sclerotia in dead plant tissue or soil.  Sclerotia can survive for five years or more in soil.  A cool, moist environment favors Sclerotinia stem rot development.  Under these conditions, sclerotia germinate to produce small, mushroom-like structures (called apothecia) that produce spores.  These spores can be spread by wind, insects, or rain splash.  In soybeans, most infections occur via open or senescing (i.e., withering) flowers.  Occasionally, the fungus will spread from plant-to-plant via direct contact of roots or other plant parts.

How can I save plants with Sclerotinia stem rot? 

SSR is difficult to control once the disease has occurred.  If affected plants are limited to a small area in a field, removal and destruction of plants may help to limit production of sclerotia that can further contaminate and cause long-term problems in the field.  This strategy usually is not feasible on a large scale, however.  If affected plants are removed, they should be burned.  DO NOT compost plants or till them into the soil.

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

To prevent introduction of the SSR fungus into soybean fields, be sure to plant sclerotia-free soybean seed.  Also, harvest fields with SSR last to avoid spreading sclerotia of the SSR fungus from field to field on combines.

Sclerotinia stem rot can cause widespread plant death and substantial yield loss.
Sclerotinia stem rot can cause widespread plant death and substantial yield loss.

In fields with a history of SSR, grow soybean cultivars that have been bred for SSR resistance.  This is the most economical and successful long-term strategy for SSR control.  In addition, consider using no-till production for three to four years as this will reduce the number of viable sclerotia near the soil surface.  Rotate soybeans with small grain crops that are not susceptible to SSR (e.g., wheat, barley, oats) to further reduce the number of viable sclerotia in the soil.  Increase row spacing and reduce soybean seeding rates to promote a more open canopy that will have better air circulation and thus dry more rapidly.  Also, make sure fields are well drained and avoid excessive irrigation especially during flowering.  Remember that the SSR fungus prefers wetter conditions; under drier conditions the fungus is less likely to infect.  Maintain good broadleaf weed control.  Weeds not only decrease air circulation and promote wetter conditions, but can also be hosts for the SSR fungus.

Finally, there are fungicides and biological control products available for SSR management.  Fungicides containing an active ingredient that is a succinate dehydrogenase inhibitor (SDHI), such as boscalid, are often effective in SSR control.  The active ingredient picoxystrobin (a type of strobilurin fungicide) has also been shown to be effective in SSR control in university research trials.  Timing of fungicide applications is critical.  Fungicides should be applied during early flowering (R1) to early pod development (R3) growth stages.  Fungicide applications made at the full pod (R4) growth stage or later will NOT be effective.  In addition, applying fungicide treatments after symptoms are visible will not be effective.  Several biocontrol agents (the most effective being one that contains a fungus called Coniothyrium minitans) have been shown to be effective in controlling SSR.  Be sure to read and follow all label instructions of the fungicide/biological control product(s) that you select to ensure that you use the materials in the safest and most effective manner possible.

For more information on Sclerotinia stem rot:  

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

This Fact Sheet is also available in PDF format:

© 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 Ted Bay, Bryan Jensen and Julie Scharm for reviewing this document.

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

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

Disease - Vegetable

Powdery Mildew – Vegetable

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UW Plant Disease Facts

 

Authors:   Brian Hudelson, UW-Madison Plant Pathology
Last Revised:   03/01/2024
D-number:   D0086
 
Vegetables such as squash and pumpkin are very susceptible to powdery mildew.
Vegetables such as squash and pumpkin are very susceptible to powdery mildew.

What is powdery mildew? 

Powdery mildews are diseases that occur on the above-ground parts (especially the leaves) of many agricultural crops (including vegetables), as well as deciduous trees and shrubs, herbaceous ornamental plants, and indoor houseplants.  Conifers are not affected by this disease.

What does powdery mildew look like? 

The name of these diseases is descriptive.  The upper and lower surfaces of leaves, as well as stems of infected plants, have a white, powdery appearance.  They look as though someone has sprinkled them with talcum powder or powdered sugar.

Where does powdery mildew come from? 

Powdery mildews are caused by many closely related fungi that survive in plant debris or on infected plants.  These fungi are fairly host specific.  The powdery mildew fungus that infects one type of plant (e.g., pumpkins) is not the same powdery mildew fungus that infects another (e.g., phlox).  However, if you see powdery mildew on one plant, then weather conditions (high humidity) are favorable for development of the disease on a wide range of plants.

How do I save a plant with powdery mildew? 

DO NOT panic!  For many plants, powdery mildews are cosmetic, non-lethal diseases.  For other plants (e.g., cucumber, squash, pumpkin), powdery mildew can cause severe leaf loss.

Peas are another vegetable that can have severe powdery mildew problems.
Peas are another vegetable that can have severe powdery mildew problems.

When a highly valued plant has had severe leaf loss due to powdery mildew for several years, you may want to consider using a fungicide for control.  Fungicides containing chlorothalonil, copper, mancozeb, myclobutanil, triadimefon, sulfur or thiophanate-methyl are registered for powdery mildew control.  A combination of baking soda (1½ tablespoons) and a light weight (i.e., paraffin-based) horticultural oil (3 tablespoons) in water (1 gallon) has also been shown to be effective.  When treating vegetables, be sure to select a product that is labeled for use on edible plants.  Most products should be applied every seven to 14 days from emergence until humid weather subsides.  DO NOT use myclobutanil, triadimefon, or thiophanate-methyl as the sole active ingredient for all treatments.  If you decide to use one of these active ingredients, alternate its use with at least one of the other listed active ingredients to help minimize problems with fungicide-resistant strains of powdery mildew fungi.  DO NOT alternate myclobutanil and triadimefon as these active ingredients are chemically related.  Be sure to read and follow all label instructions of the fungicide(s) that you select to ensure that you use the product(s) in the safest and most effective manner possible.  Also consider pretesting any product that you decide to use on a small number of leaves or plants before treating a larger area to make sure there are no toxic effects, particularly when treating during warmer weather.

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

Consider buying plant varieties that are powdery mildew resistant.  This will not guarantee that your plants will be powdery mildew free every year, but should result in less severe disease when it occurs.  Reduce the humidity around your plants by spacing them further apart to increase air flow.  Be sure not to over-water as this can lead to higher air humidity as well.  Finally, at the end of the growing season, remove and destroy any infected plant debris as this can serve as a source of spores for the next growing season.  You can burn (where allowed by local ordinance), bury or hot compost this material.

For more information on powdery 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:

© 1999-2024 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 Bill Halfman, Laura Jull, Patti Nagai and Amy Sausen 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

Powdery Mildew – Herbaceous Ornamental

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UW Plant Disease Facts

 

Authors:   Brian Hudelson, UW-Madison Plant Pathology
Last Revised:   03/01/2024
D-number:   D0084
 
Plants such as phlox, Monarda and zinnia are very susceptible to powdery mildew.
Plants such as phlox, Monarda and zinnia are very susceptible to powdery mildew.

What is powdery mildew? 

Powdery mildews are diseases that occur on the above-ground parts (especially the leaves) of many herbaceous ornamentals, as well as deciduous trees and shrubs, indoor houseplants, and many agricultural crops.  Conifers are not affected by these diseases.

What does powdery mildew look like? 

The name of these diseases is descriptive.  The upper and lower surfaces of leaves, as well as stems of infected plants, have a white, powdery appearance.  They look as though someone has sprinkled them with talcum powder or powdered sugar.

Where does powdery mildew come from? 

Powdery mildews are caused by many closely related fungi that survive in plant debris or on infected plants.  These fungi are fairly host specific.  The powdery mildew fungus that infects one type of plant (e.g., phlox) is not the same powdery mildew fungus that infects another (e.g., lilac).  However, if you see powdery mildew on one plant, then weather conditions (high humidity) are favorable for development of powdery mildews on a wide range of plants.

How do I save a plant with powdery mildew? 

DO NOT panic!  For many plants, powdery mildews are cosmetic, non-lethal diseases.  For other plants [e.g., phlox, beebalms, zinnia (see University of Wisconsin Garden Facts XHT1175)], powdery mildews can cause severe leaf loss.

Annuals such as zinnias are also very susceptible to powdery mildew.
Annuals such as zinnias are also very susceptible to powdery mildew.

When a highly valued plant has had severe leaf loss due to powdery mildew for several years, you may want to consider using a fungicide for control.  Fungicides containing chlorothalonil, copper, mancozeb, myclobutanil, triadimefon, sulfur or thiophanate-methyl are registered for powdery mildew control.  A combination of baking soda (1½ tablespoons) and a light weight (i.e., paraffin-based) horticultural oil (3 tablespoons) in water (1 gallon) has also been shown to be effective.  Most products should be applied every seven to 14 days from bud break until humid weather subsides.  DO NOT use myclobutanil, triadimefon, or thiophanate-methyl as the sole active ingredient for all treatments.  If you decide to use one of these active ingredients, alternate its use with at least one of the other listed active ingredients to help minimize problems with fungicide-resistant strains of powdery mildew fungi.  DO NOT alternate myclobutanil and triadimefon as these active ingredients are chemically related.  Be sure to read and follow all label instructions of the fungicide(s) that you select to ensure that you use the product(s) in the safest and most effective manner possible.  Also consider pretesting any product that you decide to use on a small number of leaves or plants before treating a larger area to make sure there are no toxic effects, particularly when treating during warmer weather.

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

Consider buying plant varieties that are powdery mildew resistant.  This will not guarantee that your plants will be powdery mildew free every year, but should result in less severe disease when it occurs.  Reduce the humidity around your plants by spacing them further apart to increase air flow.  Be sure not to over-water as this can lead to higher air humidity as well.  Finally, at the end of the growing season, remove and destroy any infected plant debris as this can serve as a source of spores for the next growing season.  You can burn (where allowed by local ordinance), bury or hot compost this material.

For more information on powdery 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:

© 1999-2024 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 Bill Halfman, Laura Jull, Patti Nagai and Amy Sausen 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

Powdery Mildew – Deciduous Woody Ornamentals

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UW Plant Disease Facts

 

Authors:   Brian Hudelson, UW-Madison Plant Pathology
Last Revised:   03/01/2024
D-number:   D0087
 
Many woody plants such as rose and lilac are susceptible to powdery mildew.
Many woody plants such as rose and lilac are susceptible to powdery mildew.

What is powdery mildew? 

Powdery mildews are diseases that occur on the above-ground parts (especially the leaves) of many deciduous trees and shrubs, as well as herbaceous ornamental plants, indoor houseplants, and many agricultural crops.  Conifers are not affected by these diseases.

What does powdery mildew look like? 

The name of these diseases is descriptive.  The upper and lower surfaces of leaves, as well as stems of infected plants, have a white, powdery appearance.  They look as though someone has sprinkled them with talcum powder or powdered sugar.

Where does powdery mildew come from? 

Powdery mildews are caused by many closely related fungi that survive in plant debris or on infected plants.  These fungi are fairly host specific.  The powdery mildew fungus that infects one type of plant (e.g., lilac) is not the same powdery mildew fungus that infects another (e.g., phlox).  However, if you see powdery mildew on one plant, then weather conditions (high humidity) are favorable for development of the disease on a wide range of plants.

How do I save a plant with powdery mildew? 

DO NOT panic!  For many trees and shrubs (e.g., lilac), powdery mildews are cosmetic, non-lethal disease.  For other plants (e.g., rose, ninebark) powdery mildews can cause severe leaf loss and even branch tip dieback.

Powdery mildew on ninebark can be so severe that it causes branch tip dieback.
Powdery mildew on ninebark can be so severe that it causes branch tip dieback.

When a highly valued plant has had severe leaf loss due to powdery mildew for several years, you may want to consider using a fungicide for control.  Fungicides containing chlorothalonil, copper, mancozeb, myclobutanil, triadimefon, sulfur or thiophanate-methyl are registered for powdery mildew control.  A combination of baking soda (1½ tablespoons) and a light weight (i.e., paraffin-based) horticultural oil (3 tablespoons) in water (1 gallon) has also been shown to be effective.  Most products should be applied every seven to 14 days from bud break until humid weather subsides.  DO NOT use myclobutanil, triadimefon, or thiophanate-methyl as the sole active ingredient for all treatments.  If you decide to use one of these active ingredients, alternate its use with at least one of the other listed active ingredients to help minimize problems with fungicide-resistant strains of powdery mildew fungi.  DO NOT alternate myclobutanil and triadimefon as these active ingredients are chemically related.  Be sure to read and follow all label instructions of the fungicide(s) that you select to ensure that you use the product(s) in the safest and most effective manner possible.  Also consider pretesting any product that you decide to use on a small number of leaves before treating an entire tree or shrub to make sure there are no toxic effects, particularly when treating during warmer weather.

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

Consider buying plant varieties that are powdery mildew resistant.  This will not guarantee that your plants will be powdery mildew free every year, but should result in less severe disease when it occurs.  Reduce the humidity around your plants by spacing them further apart to increase air flow.  In established trees and shrubs, thin canopies to increase air flow.  Be sure not to over-water as this can lead to higher air humidity as well.  Finally, at the end of the growing season, remove and destroy any infected plant debris as this can serve as a source of spores for the next growing season.  You can burn (where allowed by local ordinance), bury or hot compost this material.

For more information on powdery 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:

© 1999-2024 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 Bill Halfman, Laura Jull, Patti Nagai and Amy Sausen 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

Rose Rust

Extension Logo

UW Plant Disease Facts

 

Authors:   Robyn Roberts*, UW-Madison Plant Pathology
Last Revised:   03/01/2024
D-number:   D0098

What is rose rust? 

Rose rust is a common fungal disease found in much of North America (including the continental United States) and Europe.  Rose rust affects many varieties of rose, though some varieties (e.g., hybrids) are more prone to the disease.  Rose rust has been a perennial problem along the Pacific Coast of the United States where mild temperatures and high moisture are favorable for rust development.  In the Midwest, extremes in winter and summer temperatures have historically tended to be less favorable for the disease.  However, recent climate changes in Wisconsin have led to rose rust becoming more commonplace in the state.

Yellow spots on upper leaf surfaces with corresponding powdery, orange to black spots on lower leaf surfaces are typical of rose rust.
Yellow spots on upper leaf surfaces with corresponding powdery, orange to black spots on lower leaf surfaces are typical of rose rust.

What does rose rust look like? 

Rose rust often first appears on lower leaves, but eventually an entire plant can be affected.  Typical symptoms include general yellowing of leaves followed by eventual leaf death.  Affected rose stems (i.e., canes) can become curled and distorted.  As the disease progresses, powdery orange or black, circular spots (called pustules) containing spores of the fungus that causes the disease form on the undersides of leaves.  Corresponding yellow spots are visible on upper leaf surfaces above the pustules.  Pustules may also form on stems and green flower parts (sepals).  Rose rust usually develops in the spring and fall (when favorable mild temperatures and wet conditions are more common), but the disease can affect roses during the summer months as well.

Where does rose rust come from? 

Rose rust is caused by several species of fungi in the genus Phragmidium.  These fungi specifically infect roses.  Rose rust is often introduced into a garden on infected shrubs purchased from a nursery or other rose supplier.  Once introduced into a garden, rose rust fungi can overwinter in rose leaf debris, as well as on infected rose canes.  In the spring, spores produced in debris and on canes can blow to newly emerging rose foliage, leading to new infections.

How do I save a plant with rose rust? 

Control of rose rust is difficult once symptoms develop.  Prune out affected canes and remove leaves as symptoms develop to prevent the spread of rust fungi to other rose shrubs.  Destroy these materials by burning (where allowed by local ordinances) or burying them.  In the fall, remove and destroy any remaining dead leaves and other rose debris to eliminate places where rose rust fungi can overwinter.  If you notice a rust problem very early (before there are many symptoms), fungicide treatments may be useful for managing the disease; however, most fungicides work best when applied before any symptoms appear.  If you decide to use fungicides for rust control, select products that are labeled for use on roses and that contains the active ingredients chlorothalonil, mancozeb, myclobutanil, propiconazole, sulfur or triforine.  Treat every seven to 10 days, and DO NOT use the same active ingredient for all treatments, particularly if you decide to use myclobutanil, propiconazole or triforine.  Instead, alternate use of the two active ingredients listed above to help minimize potential problems with fungicide-resistant strains of rose rust fungi.  DO NOT alternate myclobutanil, propiconazole or triforine, as these active ingredients are chemically related.  Be sure to read and follow all label instructions of the fungicides that you select to ensure that you use these products in the safest and most effective manner possible.

How do I avoid problems with rose rust in the future?  

Whenever possible, plant rose varieties that are less susceptible to rose rust (i.e., avoid hybrid varieties).  Always inspect new rose shrubs for rose rust (and other diseases) prior to purchase.  DO NOT bring diseased shrubs into your garden.  Plant rose shrubs far enough apart so that their foliage does not overlap, and thin your roses on a regular basis.  Proper planting and pruning promote good air circulation that will facilitate rapid drying of leaves and canes, thus making the environment less favorable for rust development.  Avoid working with your roses when they are wet as you are more likely to spread rust spores under these conditions.  Fertilize and water roses appropriately.  Well-cared-for plants tend to be less susceptible to disease.  When watering, apply water at the base of your shrubs (e.g., with a soaker or drip hose) rather than over the leaves (e.g., with a sprinkler).  Watering with a sprinkler tends to spread rust spores and wets leaves and canes, thus providing a more favorable environment for rust infections to occur.

For more information on rose rust: 

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

This Fact Sheet is also available in PDF format:

*Completed as partial fulfillment of the requirements for Plant Pathology 558 at the University of Wisconsin Madison.

© 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 Erica Arcibal, Rosemarie Bugs, Lisa Johnson, Cyndy King, Janet Roberts, Jillian Roberts and Rose Roberts 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 - Herbaceous Ornamental, Disease - Vegetable, Turf

Root-Knot Nematode

Extension Logo

UW Plant Disease Facts

 

Authors:   Nolan Bornowski*, UW-Madison Plant Pathology
Last Revised:   03/01/2024
D-number:   D0097
 

Root-knot nematodes (Meloidogyne spp.) are small, soilborne, worm-like organisms that infect many agricultural and horticultural plants.  Root-knot nematodes are found worldwide, and are named for the swellings (called “galls” or “knots”) that they cause on plant roots.  Economically-important species of Meloidogyne include M. arenaria, M. hapla, M. incognita, and M. javanica.  Of these, M. hapla (commonly known as Northern root-knot nematode) is most likely to be found in Wisconsin soils.

Root-knot nematodes cause swollen, distorted roots that can interfere with movement of water and nutrients within a plant.
Root-knot nematodes cause swollen, distorted roots that can interfere with movement of water and nutrients within a plant.

Appearance:  

Root-knot nematodes are about 1/10 the size of a pinhead and are typically embedded inside roots.  They are impossible to see with the naked eye.  Juvenile root-knot nematodes (both males and females), as well as adult males, are vermiform (i.e., worm-shaped) and live in the soil.  Adult females are spherical in shape and live inside roots.  Both males and females possess a thin, tube-like structure called a stylet that they use for penetrating root tissue.

Symptoms and Effects: 

When root-knot nematodes enter roots, they release chemicals that cause nearby root cells to enlarge.  This leads to the formation of swollen, distorted areas in roots known as galls or knots.  The number and size of galls varies depending on plant species and cultivar, and the number of root-knot nematodes in the soil.  On some hosts (e.g., grasses) root swelling can be very difficult to detect.  Nematode feeding interferes with proper root function (e.g., water and nutrient movement).  Thus, infected plants may be stunted and wilted, may exhibit discolorations (e.g., yellowing) typical of plants with nutrient deficiencies, and ultimately (in field or vegetable crops) may have lower yields.  Because root-knot nematodes tend not to be uniformly distributed in the soil, symptomatic plants often occur in patches and are typically surrounded by plants of normal height and appearance.  Environmental factors such as slope, soil type, or soil moisture can cause similar patchy patterns, so identification of a root-knot nematode problem requires examination of symptomatic plants at a lab qualified to perform nematode diagnostics.

Life Cycle: 

Root-knot nematodes (i.e., M. hapla) are native to Wisconsin and can be spread whenever contaminated soil or infected plants are moved.  Root-knot nematodes survive the winter as eggs in the soil.  Like insects, root-knot nematodes have several juvenile stages and the nematodes molt (i.e., shed their outer layers) as they grow.  The second juvenile stage of root-knot nematode is the most important, because at this stage the nematode seeks out and infects plant roots.  Once it has entered a root, a root-knot nematode molts three more times before becoming an adult.  A male root-knot nematode is able to move about freely and can leave a root.  A female root-knot nematode remains and feeds in a given location within a root.  Eventually, a female enlarges to the point where a portion of her body extends to the root surface and this allows her to lay her eggs in the soil.  In some hosts, eggs can also be found within the galls.

Control: 

If you are having a root-knot nematode problem in your garden, consider crop rotation and the use of cover crops as management tools.  See University of Wisconsin Garden Facts XHT1210, Crop Rotation in the Home Vegetable Garden and XHT1209, Using Cover Crops and Green Manures in the Home Vegetable Garden for details.  If used properly, these techniques can be effective in reducing the number of root-knot nematodes in the soil.  M. hapla, the root-knot nematode species most common in Wisconsin, does not infect corn, wheat, oats or rye, so use of these crops in a rotation or as cover crops often provides great benefit.

Cover crops of French marigolds (Tagetes patula) also have been shown to reduce the number of root-knot nematodes in soil.  This common garden ornamental releases a chemical (alpha-terthienyl) that is highly toxic to root-knot nematodes and prevents their eggs from hatching.  As an added bonus, root-knot nematodes are not able to develop properly in marigold roots.  When using crop rotation or cover crops, proper broadleaf weed control is critical because weeds can provide a place for root-knot nematodes to survive and reproduce.

Finally, consider amending the soil in your garden with organic matter such as compost or leaf mulch.  Such amendments tend to increase the diversity of microorganisms in the soil and can encourage the growth of certain soilborne fungi that ensnare and feed on root knot nematodes, and parasitize their eggs.

For more information on root-knot nematode: 

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 558 at the University of Wisconsin Madison.

© 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 Freddie Bornowski, Ashley Ellinghuysen, Amy Kispert, Ian McCue , Ann MacGuidwin, Scott Reuss and Ken Schroeder 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

Root Rots on Houseplants

What is root rot?

Root rot is a general term that describes any disease where the pathogen (causal organism) causes the deterioration of a plant’s root system. Most plants are susceptible to root rots, including both woody and herbaceous ornamentals. Root rots can be chronic diseases or, more commonly, are acute and can lead to the death of the plant.

Wilting of poinsettia associated with Pythium root rot.
Wilting of poinsettia associated with Pythium root rot.

How do you know if your plant has a root rot?

Homeowners often become aware of root rots when they note that a plant is wilted, even though the soil is wet. Plants with root rots are also often stunted, and may have leaves with a yellow or red color, symptoms that suggest a nutrient deficiency. Careful examination of the root systems of these plants reveals roots that are soft and brown. These roots may have a bad odor.

Where does root rot come from?

A large number of soil-borne fungi cause root rots. Pythium spp., Phytophthora spp., Rhizoctonia solani, and Fusarium spp. are the most common root rot fungi. These fungi have wide host ranges, and thus can cause root rots on a wide variety of plants. Most root rot fungi prefer wet soil conditions and some, such as Pythium and Phytophthora produce spores that can survive for long periods in soil or plant debris.

How do I save a plant with root rot?

Often the best and most cost effective way of dealing with a plant with root rot is to throw it out. If you decide to keep a plant with root rot, REDUCE SOIL MOISTURE! Provide enough water to fulfill the plant’s growth needs and prevent drought stress, but DO NOT over-water. We DO NOT recommend use of chemical fungicides for control of root rots on houseplants because of the limited availability of products for use by homeowners, and because those products that are available tend to be expensive.

How do I avoid problems with root rots?

First, buy plants from a reputable source and make sure they are root rot-free prior to purchase. Second, replant your houseplants properly. Use a pot with drainage holes, but DO NOT put rocks or gravel at the bottom of the pot. The presence of rocks or gravel can actually inhibit drainage. Use a pasteurized commercial potting mix, NOT soil from your garden. Garden soils often contain root rot fungi. Add organic material (e.g., peat moss) to heavy potting mixes to increase drainage. Third, minimize potential contamination of your plants with root rot fungi. DO NOT reuse potting mix from your houseplants, or water that has drained from your plants, as both potentially can contain root rot fungi. After working with plants with root rot problems, disinfest tools, working surfaces and clay pots with a 10% bleach or detergent solution, or alcohol. DO NOT reuse plastic pots as they are often difficult to disinfest adequately. Finally and most importantly, moderate plant moisture. Provide enough water to fulfill your plants’ needs for growth and prevent drought stress, but DO NOT over-water. In particular, DO NOT allow plants to sit in drainage water. REMEMBER, root rot fungi grow and reproduce best in wet soils.

For more information on root rots:

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

Disease - Herbaceous Ornamental, Disease - Vegetable

Root Rots in the Garden

Extension Logo

UW Plant Disease Facts
 
Authors:   Brian Hudelson, UW-Madison Plant Pathology and Laura Jull, UW-Madison Horticulture
Last Revised:   03/01/2024
D-number:   D0095
 
Brown discoloration of roots typical of root rots.
Brown discoloration of roots typical of root rots.

What is root rot? 

Root rot is a general term that describes any disease where the pathogen (causal organism) attacks and leads to the deterioration of a plant’s root system.  Most plants are susceptible to root rots, including both woody and herbaceous ornamentals.  Root rots can be chronic diseases or, more commonly, are acute and can lead to the death of the plant.

What does root rot look like? 

Gardeners often become aware of root rot problems when they see above ground symptoms of the disease.  Plants with root rot are often stunted, wilted, or have top-down dieback.  They may also have leaves with a yellow or red color, suggesting a nutrient deficiency.  Examination of the roots of these plants reveals tissue that is soft and brown.

Where does root rot come from? 

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

How do I save a plant with root rot? 

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

Stunting, top-down dieback, and red or yellow foliage can indicate a root rot problem.
Stunting, top-down dieback, and red or yellow foliage can indicate a root rot problem.

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

How do I avoid problems with root rots? 

Buy plants from a reputable source and make sure they are root rot-free prior to purchase.  Establish healthy plants in a well-drained site.  Moderate soil moisture; add organic material (e.g., leaf litter or compost) to heavy soils to increase soil drainage, and DO NOT over-water.  Provide just enough water to fulfill a plant’s needs for growth and prevent drought stress.  Also, DO NOT apply more than three inches of mulch in flowerbeds.  Excessive mulching can lead to over wet soils, which favor root rot fungi growth and reproduction.  Finally, minimize movement of root/crown rot fungi in your garden.  DO NOT move soil or plants from areas where plants are having root rot problems.  DO NOT water plants with water contaminated with soil (and thus potentially with root rot organisms).  After working with plants with root rot, decontaminate tools and footwear by treating for at least 30 seconds with a 10% bleach solution or 70% alcohol (e.g., rubbing alcohol, certain spray disinfectants).  If you use bleach to decontaminate metal tools, be sure to thoroughly rinse and oil your tools after you are done gardening to prevent rusting.

For more information on root rots: 

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

This Fact Sheet is also available in PDF format:

© 2000-2024 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, Ann Joy and Sharon Morrisey for reviewing this document.

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

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

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

Root and Crown Rots

Extension Logo

UW Plant Disease Facts

 

Authors:   Brian Hudelson, UW-Madison Plant Pathology and Laura Jull, UW-Madison Horticulture
Last Revised:   03/01/2024
D-number:   D0094
 
Discoloration of maple crown and roots typical of Phytophthora root/crown rot.
Discoloration of maple crown and roots typical of Phytophthora root/crown rot.

What is root/crown rot? 

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

What does root/crown rot look like? 

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

Where does root/crown rot come from? 

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

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

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

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

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

How do I avoid problems with root/crown rots?  

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

For more information on root/crown rots: 

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

This Fact Sheet is also available in PDF format:

© 2000-2024 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, Ann Joy and Sharon Morrisey for reviewing this document.

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

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