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.
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.
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.
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.qa.webhosting.cals.wisc.edu.
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.
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.
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.qa.webhosting.cals.wisc.edu.
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.
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.
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.
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.qa.webhosting.cals.wisc.edu.
Authors: Ann Joy and Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 03/01/2024
D-number: D0088
What is powdery scab?
Powdery scab is a potentially serious disease of potatoes that occurs worldwide in regions where potatoes are grown, including Wisconsin. Although powdery scab primarily causes cosmetic, if unsightly, skin blemishes of potato tubers, the pathogen that causes the disease can transmit another, more serious potato pathogen, Potato mop-top virus (PMTV). PMTV was first detected in Wisconsin in 2020. This virus can cause severe losses and can limit a seed potato producer’s ability to sell to certain foreign markets. In addition, blemishes caused by powdery scab can serve as entry points for other pathogens, such as those that cause late blight (see UW Plant Disease Facts D0068, Late Blight, pink rot, dry rot and black dot.
Powdery scab can lead to development of crater-like lesions on the surface of potato tubers. (Photo courtesy of Anette Phibbs)
What does powdery scab look like?
Tubers are infected through lenticels, eyes, or wounds. Initial symptoms of tuber infection are sunken purple-brown lesions that are followed by pimple-like swellings. As lesions mature, they break through the potato skin and develop into shallow depressions that contain a mass of powdery spore balls (called cystosori) surrounded by thin, raised remnants of the outer tuber skin. When infections develop in wet soils, the lesions deepen and become open cankers. Infections of roots and stolons can also occur, and first appear as necrotic spots, that later become small, white to tan-colored galls. As galls mature, they enlarge, turn brown and finally break open releasing cystosori into the soil. Because powdery scab symptoms appear on below-ground parts of the potato, infections may not be noticed until harvest. If symptoms have not fully developed by harvest, they may continue to develop in storage. At various stages of development, powdery scab can be mistaken for common scab (see UW Plant Disease Facts D0083, Potato Scab), potato wart, black scurf, and root-knot nematode damage (see UW Plant Disease Facts D0097, Root-Knot Nematode).
Where does powdery scab come from?
Powdery scab is caused by the soil-borne slime mold, Spongospora subterranea f. sp. subterranea. The pathogen can be introduced into a non-infested field on infected seed tubers; on equipment, shoes, and other clothing contaminated with infested soil; or in infested manure (cystosori can survive passage through animal guts). S. subterranea f. sp. subterranea cystosori can survive for at least 6 years in the soil. In addition, S. subterranea f. sp. subterranea can survive on a variety of solanaceous vegetables and weeds including volunteer potatoes, tomatoes, peppers, nightshade, ground cherry and jimsonweed. Cool temperatures (52ºF to 64ºF) and wet conditions favor disease development. When free water is available, cystosori release motile spores (called zoospores) that swim to and infect root hairs, stolons and tubers. Alternating periods of wet and dry weather produce repeated cycles of zoospore release. Environmental conditions appear to be more important in disease development than initial inoculum level.
Powdery scab symptoms on a red-skinned variety of potato. (Photo courtesy of Anette Phibbs)
How do I control powdery scab?
The best way to manage powdery scab is to prevent introduction of the pathogen into potato fields. The introduction of the powdery scab pathogen into Wisconsin is thought to have occurred when growers planted infected seed tubers. Therefore, carefully inspect seed tubers for powdery scab symptoms and be sure to plant disease-free seed potatoes into non-infested fields. Once fields become infested, avoid these fields if possible, particularly those with poorly drained soils. Contaminated fields should be rotated away from potatoes (and other susceptible hosts, such as tomatoes) for three to 10 years. During this period, be sure to keep solanaceous weeds (e.g., nightshade, ground cherry) under control as these plants can serve as alternate hosts for the pathogen. Once potato production resumes in infested fields, be sure not to over-irrigate, especially during tuber set. Adopting a later planting date to take advantage of warmer temperatures may help reduce the level of powdery scab, but this may not be possible given other management constraints. When attempting to dispose of infected tubers, do not compost these tubers. If you decide to use infected tubers as feed, do not use manure from animals that have been fed the tubers, as cystosori can survive passage through animal guts. Research by USDA-ARS scientists indicates that some mustard family crops (e.g., white mustard, rape, canola) that produce high levels of glucosinolates, when grown as green manures (fall-planted, spring-incorporated), may reduce levels of powdery scab. Fungicides containing the active ingredient fluazinam have shown some efficacy against powdery scab, but results have been variable. If you decide to use fungicides for control, be sure to select a product that is labeled for use on potatoes, and be sure to read and follow all label instructions of the fungicide that you select to ensure that you use the product in the safest and most effective manner possible.
For more information on powdery scab:
SContact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
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 Adrian Barta, Anette Phibbs, Walt Stevenson and Ken Williams for reviewing this document.
A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.qa.webhosting.cals.wisc.edu.
Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 03/01/2024
D-number: D0083
What is potato scab?
Potato scab is a common and disfiguring disease of potato tubers that affects potatoes wherever they are grown. Thin-skinned potato varieties tend to be more severely affected. This disease can also affect other root vegetables such as beets, carrots, parsnip, radish, rutabaga, salsify and turnip.
Sunken or raised, corky spots on potato tubers are characteristic of potato scab.
What does potato scab look like?
Symptoms of scab are typically evident at harvest and vary widely depending upon potato variety and environmental conditions during tuber development. Classic symptoms of scab include scab-like raised or slightly sunken rough, corky patches on tuber or root surfaces. Under extreme conditions, large, deep pits may form.
Where does potato scab come from?
Potato scab is caused by the bacterium Streptomyces scabies. This bacterium is related to certain bacteria that produce antibiotics used to treat human diseases. S. scabies occurs naturally in many soils, from soils with high organic matter content, to coarse and gravelly soils that tend to dry quickly. S. scabies can also be introduced into garden soils when infected tubers are used as seed stock.
What do I do with potato tubers that have potato scab?
Scabby potato tubers, while unsightly, are still edible. Infected potatoes need only be peeled before use. Store tubers with scab in a cool, dark, dry place to reduce the possibility of scabby areas becoming infected by soft rot bacteria that will totally decay tubers (see UW Plant Disease Facts D0010, Bacterial Soft Rot).
How do I avoid problems with potato scab in the future?
Use certified, scab-free seed potatoes in your garden. DO NOT use infected tubers to produce seed pieces. Select potatoes varieties such as Norland, Russet Burbank and Superior that have at least moderate resistance to scab. Try not to plant potatoes in the same spot in your garden more frequently than once every three years. Rotate potatoes with crops such as corn, peas, and beans that are not susceptible to scab. Scab tends not to develop when the soil pH is less than 5.2. Therefore, acidify garden soils (i.e., make sure the soil pH is less than 7) where possible. For home gardens, keeping the soil pH at approximately 6.5 is a good compromise when growing not only potatoes, but other vegetable crops. Avoid using fertilizers (e.g., lime, calcium and potassium nitrate, or fresh manure) that may increase soil pH. Finally, make sure to adequately water your potatoes, particularly as tubers are forming.
For more information on potato scab:
Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
An EEO/Affirmative Action employer, University of Wisconsin-Madison Division of Extension provides equal opportunities in employment and programming, including Title IX and ADA requirements. This document can be provided in an alternative format by calling Brian Hudelson at (608) 262-2863 (711 for Wisconsin Relay).
References to pesticide products in this publication are for your convenience and are not an endorsement or criticism of one product over similar products. You are responsible for using pesticides according to the manufacturer’s current label directions. Follow directions exactly to protect the environment and people from pesticide exposure. Failure to do so violates the law.
Thanks to Karen Delahaut, Lis Friemoth, and Ann Joy for reviewing this document.
A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.qa.webhosting.cals.wisc.edu.
Authors: Amanda Gevens, Anna Seidl y Brian Hudelson, Departamento de Patología de Plantas, UW-Madison Traducido por Marisol López
Last Revised: 05/11/2011
D-number: D0068S
Tizón Tardío
¿Qué es el tizón tardío?
El tizón tardío es una enfermedad destructiva de los tomates y de las papas que puede matar a las plantas maduras y causar que los frutos del tomate y los tubérculos de la papa no sean comestibles. Esta enfermedad también afecta, aunque típicamente en menor grado, a las berengenas y a los pimientos así como a malezas relacionadas como la hierba mora. Históricamente, el tizón tardío fue el responsable de la hambruna irlandesa de la papa, que causó la muerte de por lo menos un millón de irlandeses, y la emigración de otro millón de ellos a Gran Bretaña, Estados Unidos, Australia, Canadá y otros países. Recientemente, la enfermedad causó pérdidas graves a productores de tomates frescos para el mercado y a jardineros en Wisconsin.
El tizón tardío puede diezmar a las plantas de tomate y papa en siete a diez días si las condiciones del clima son frescas y húmedas.
¿Cómo es el tizón tardío?
En las hojas del tomate y la papa, el tizón tardío comienza a verse como áreas de color verde claro o verde olivo que rápidamente se agrandan volviendose marrón negruzcas, como empapadas de agua y de apariencia oleosa. Los tallos también pueden exhibir áreas de color marrón oscuro a negro. Si las condiciones del clima son frescas y húmedas, las plantas enteras pueden colapsar y morir de tizón tardío en 7 a 10 días. Los frutos del tomate con tizón tardío desarrollan manchas grandes, firmes, casi siempre hundidas, de color dorado a marrón chocolate y con anillos distintivos. Los tubérculos de papa con la enfermedad, desarrollan áreas con una decoloración rojiza a marrón debajo de la cáscara que pueden después hundirse. El tejido de la hoja, tallo, fruto o tubérculo, afectado con la enfermedad, con el tiempo casi siempre desarrolla un aspecto velloso de blanco a gris, cuando el organismo de tizón tardío comienza a reproducirse. Otras enfermedades del tomate y la papa como la mancha de la hoja causada por Septoria (vea University of Wisconsin Garden Facts XHT1073), tizón temprano (vea University of Wisconsin Garden Facts XHT1074) y marchitez causada por Verticillium pueden ser confundidas con tizón tardío.
¿Cómo evito problemas de tizón tardío en el futuro?
En la primavera, elimine cualquier planta voluntaria de tomate o de papa (y malezas como hierba mora) de la manera descrita anteriormente. Todas estas plantas son fuentes posibles de P. infestans. Por el mismo motivo, NO use los tubérculos de la cosecha de papa de un año anterior como semillas de papa. En lugar de eso, compre cada año semillas de papa certificadas de un proveedor reputable. También considere plantar variedades de tomate resistentes al tizón tardío. Esas variedades incluyen “Better Boy”, “Golden Sweet”, “Green Zebra”, “Juliet”, “Legend”, “Magic Mountain”, “Matt’s Wild Cherry”, “Pruden’s Purple”, “Regal Plum”, “Roma”, “Slava”, “Stupice”, “Sun Sugar”, “Wapsipinicon”, y “Wisconsin 55”. El desempeño de estas variedades puede variar dependiendo de la variante de P. infestans que está presente en una temporada de cultivo en particular, y también dependiendo de las condiciones del clima. Sin embargo, “Magic Mountain” y “Regal Plum” han demostrado una excelente resistencia a muchas variantes del organismo de tizón tardío en un amplio rango de condiciones ambientales.
Los fungicidas también pueden ser usados para reducir el impacto del tizón tardío. Sin embargo, las aplicaciones de fungicidas, para que sean efectivas, deben de hacerse antes de que comience la enfermedad. Las aplicaciones de fungicidas no son necesarias durante períodos de clima caliente y seco porque P. infestans no tiene probabilidades de ser activo bajo estas condiciones. Los fungicidas tienen la mayor probabilidad de ser efectivos durante períodos de clima fresco y húmedo. Sin embargo, si las condiciones del clima son excesivamente frescas y húmedas, aunque el fungicida se aplique en el tiempo apropiado quizás no provea un control adecuado contra el tizón tardío. Si usted decide usar fungicidas, seleccione un producto específico para el uso en tomates (o papas) y que contenga chorotalonil o cobre como ingrediente activo. Algunos, pero no todos, los productos que contienen cobre pueden ser usados para la producción de vegetales orgánicos. Asegúrese de seguir las indicaciones de la etiqueta para garantizar que el producto que usted seleccione sea usado de la manera más segura y efectiva posible.
¿De dónde viene el tizón tardío?
El tizón tardío es causado por el hongo acuático Phytophthorainfestans. Hay varias variantes de este organismo. Algunas variantes causan problemas severos en los tomates; otras son un problema mayor en las papas. P. infestans puede ser introducido cuando las esporangias (es decir, estructuras similares a las esporas) del organismo son transportadas a un área donde prevalecen vientos. P. infestans también puede ser introducido en plantas infectadas (ej. plántulas de tomates) o tubérculos de papas que han sido traídos a un área para la venta. Es improbable que P. infestans sobreviva durante el invierno en los suelos de Wisconsin. Sin embargo, el organismo puede sobrevivir en restos de plantas infectadas que permanecen vivas durante el invierno. Estos restos de plantas pueden incluir plantas de tomate infectadas con P. infestans o frutos mantenidos temperados en acumulaciones de abono, y tubérculos de papas infectados con P. infestans que han quedado en la tierra después de la cosecha o que han sido almacenadas en un lugar cálido.
¿Cómo salvo a una planta con tizón tardío?
Las plantas que muestran síntomas de tizón tardío no pueden ser salvadas y deben de ser eliminadas de forma inmediata para limitar la propagación de P. infestans a otras plantas. Para los jardineros caseros, el método preferido de eliminación es sacar las plantas afectadas (con raíz y todo) y ponerlas en bolsas de plástico. Las bolsas deberán dejarse al sol por algunos días para asegurarse que las plantas, así como cualquier P. infestans, estén totalmente muertos. Las plantas en las bolsas pueden luego ponerse en la basura para ser recogida. Las plantas o partes de plantas enfermas (ej. frutos del tomate o tubérculos de papa) NO deben de ser usados para hacer abono. Los frutos de plantas de tomate afectadas por tizón tardío que se vean saludables se pueden comer o conservar sin peligro. Sin embargo, antes de intentar conservar cualquier fruta o vegetal, contacte a la oficina de UW-Extensión de su condado para obtener las instrucciones más actualizadas sobre la conservación de alimentos. Una vez que los frutos del tomate o los tubérculos de la papa comienzan a presentar los síntomas de tizón tardío, NO deben de ser comidos o enlatados o conservados de alguna otra manera.
En las hojas del tomate (izquierda), el tizón tardío produce áreas de color marrón negruzcas, como empapadas de agua y de apariencia oleosa que pueden tener aspecto velloso de blanco a gris. En los frutos del tomate (derecha), el tizón tardío produce manchas grandes, firmes, casi siempre hundidas, de color dorado a marrón chocolate, con anillos distintivos.
¿Cómo evito problemas de tizón tardío en el futuro?
En la primavera, elimine cualquier planta voluntaria de tomate o de papa (y malezas como hierba mora) de la manera descrita anteriormente. Todas estas plantas son fuentes posibles de P. infestans. Por el mismo motivo, NO use los tubérculos de la cosecha de papa de un año anterior como semillas de papa. En lugar de eso, compre cada año semillas de papa certificadas de un proveedor reputable. También considere plantar variedades de tomate resistentes al tizón tardío. Esas variedades incluyen “Better Boy”, “Golden Sweet”, “Green Zebra”, “Juliet”, “Legend”, “Magic Mountain”, “Matt’s Wild Cherry”, “Pruden’s Purple”, “Regal Plum”, “Roma”, “Slava”, “Stupice”, “Sun Sugar”, “Wapsipinicon”, y “Wisconsin 55”. El desempeño de estas variedades puede variar dependiendo de la variante de P. infestans que está presente en una temporada de cultivo en particular, y también dependiendo de las condiciones del clima. Sin embargo, “Magic Mountain” y “Regal Plum” han demostrado una excelente resistencia a muchas variantes del organismo de tizón tardío en un amplio rango de condiciones ambientales.
Los fungicidas también pueden ser usados para reducir el impacto del tizón tardío. Sin embargo, las aplicaciones de fungicidas, para que sean efectivas, deben de hacerse antes de que comience la enfermedad. Las aplicaciones de fungicidas no son necesarias durante períodos de clima caliente y seco porque P. infestans no tiene probabilidades de ser activo bajo estas condiciones. Los fungicidas tienen la mayor probabilidad de ser efectivos durante períodos de clima fresco y húmedo. Sin embargo, si las condiciones del clima son excesivamente frescas y húmedas, aunque el fungicida se aplique en el tiempo apropiado quizás no provea un control adecuado contra el tizón tardío. Si usted decide usar fungicidas, seleccione un producto específico para el uso en tomates (o papas) y que contenga chorotalonil o cobre como ingrediente activo. Algunos, pero no todos, los productos que contienen cobre pueden ser usados para la producción de vegetales orgánicos. Asegúrese de seguir las indicaciones de la etiqueta para garantizar que el producto que usted seleccione sea usado de la manera más segura y efectiva posible.
Para obtener más información sobre tizón tardío:
Vea el boletín UW-Extensión A3422, o contacte al agente de Extensión de su condado.
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.
Gracias a Ann Joy, Kristin Krokowski, Barb Larson, Maria del Pilar Marquez, Patti Nagai y Ann Wied por revisar este documento.
A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.qa.webhosting.cals.wisc.edu.
Authors: Amanda Gevens, Anna Seidl and Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 03/01/2024
D-number: D0068
What is late blight?
Late blight is a destructive disease of tomatoes and potatoes that can kill plants, and make tomato fruits and potato tubers inedible. This disease also affects, although typically to a lesser extent, weeds such as nightshade. Historically, late blight was responsible, in part, for the Irish potato famine, which led to the death of at least one million Irish, and the emigration of another one million Irish to Great Britain, the United States, Australia, Canada and other countries. The disease routinely causes severe losses for fresh market tomato producers and home gardeners in Wisconsin.
Late blight can decimate tomato and potato plants in seven to 10 days if weather conditions are cool and wet.
What does late blight look like?
On leaves of tomato or potato, late blight begins as pale-green or olive-green areas that quickly enlarge to become brown-black, water-soaked, and oily-looking. Stems can also exhibit dark-brown to black areas. If weather conditions are cool and wet, entire plants can collapse and die from late blight in seven to 10 days. Tomato fruits with late blight develop large, often sunken, golden- to chocolate-brown, firm spots with distinct rings. Potato tubers with the disease develop a reddish-brown discoloration under the skin and these areas may become sunken. Affected leaf, stem, fruit or tuber tissue often eventually develops a white-gray, fuzzy look as the late blight organism begins to reproduce. Other tomato and potato diseases such as Septoria leaf spot (see UW Plant Disease Facts D0100, Septoria Leaf Spot), early blight (see UW Plant Disease Facts D0046, Early Blight) and Verticillium wilt (see UW Plant Disease Facts D0122, Verticillium Wilt of Vegetables) may be misidentified as late blight.
Where does late blight come from?
Late blight is caused by the fungus-like water mold Phytophthora infestans. There are several variants or strains of this organism. Some variants/strains cause more severe problems on tomatoes; others are more of a problem on potatoes. P. infestans can be introduced when sporangia (i.e., spore-like structures) of the organism are blown into an area on prevailing winds. P. infestans can also be introduced on infected plants (e.g., tomato seedlings) or potato tubers that are brought into an area for sale. P. infestans is unlikely to survive over the winter in Wisconsin soils. However, the organism can survive on infected plant material that remains alive through the winter. Such plant materials can include P. infestans-infected tomato plants or fruits kept warm in compost piles, and P. infestans infected potato tubers that have remained in the soil after harvest or have been stored in a warm place.
How do I save a plant with late blight?
Plants showing symptoms of late blight cannot be saved and should be disposed of immediately to limit spread of P. infestans to other plants. For home gardeners, the preferred method of disposal is to pull affected plants (roots and all), and place them in plastic bags. The bags should be left in the sun for a few days to make sure that plants, as well as any P. infestans, are totally killed. Bagged plants should then be put out for trash pickup. Diseased plants or plant parts (e.g., tomato fruits or potato tubers) should NOT be composted. Healthy-looking fruits from late-blight-affected tomato plants are safe to eat or preserve. However, before attempting to preserve any fruit or vegetable, contact your county UW-Extension office for the most current food preservation instructions. Once tomato fruits or potato tubers begin to show symptoms of late blight, they should NOT be eaten, nor should they be canned or otherwise preserved.
On tomato leaves (left), late blight leads to brown-black, water-soaked, oily areas that may have a white-gray fuzzy look. On tomato fruits (right), late blight leads to large, often sunken, golden- to chocolate-brown, firm spots with distinct rings.
How do I avoid problems with late blight in the future?
In the spring, dispose of any volunteer tomato and potato plants (as well as weeds such as nightshade) as described above. All of these plants are potential sources of P. infestans. For the same reason, DO NOT use tubers from a previous year’s potato crop as seed potatoes. Instead purchase certified seed potatoes from a reputable supplier each year. Also, consider planting tomato varieties with late blight tolerance or resistance. Such varieties include ‘Defiant PHR’, ‘Iron Lady’, ‘Jasper’, ‘JTO-545’, ‘Lemon Drop’, ‘Matt’s Wild Cherry’, ‘Mountain Magic’, ‘Mountain Merit’, ‘Mr. Stripey’, ‘Plum Regal’, ‘Pruden’s Purple’, ‘Stellar’ and ‘Wapsipinicon Peach.’ The performance of these varieties may vary depending on the variant or strain of P. infestans that is present in a particular growing season, and depending on the weather conditions. Consider planting several resistant tomato varieties to help ensure that no matter what P. infestans variant is prevalent in a given year, you will have some healthy tomato plants and fruits.
Fungicides also can be used to reduce the impact of late blight. However, fungicide applications must be made prior to the onset of disease or they will be ineffective. Fungicide applications are not needed during periods of hot, dry weather as P. infestans is not likely to be active under these conditions. Fungicides are most likely to be useful during periods of cool, wet weather. However, if weather conditions are excessively cool and wet, even properly-timed fungicide applications may not provide adequate late blight control. If you decide to use fungicides, select a product that is labeled for use on tomatoes (or potatoes) and that contains chlorothalonil or copper as the active ingredient. Certain, but not all, copper-containing products can be used for organic vegetable production. Be sure to follow all label instructions to ensure that you use the product that you select in the safest, most effective means possible. For more information on home garden fungicides for vegetable disease control, see UW Plant Disease Facts D0062, Home Vegetable Garden Fungicides.
For more information on late blight:
Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
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 Kristin Krokowski, Barb Larson, Patti Nagai and Ann Wied for reviewing this document.
A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.qa.webhosting.cals.wisc.edu.
Authors: Ann Joy and Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 03/01/2024
D-number: D0067
Ringspots on coleus leaf caused by impatiens necrotic spot virus. (Photo courtesy of Margaret Daughtrey)
What is impatiens necrotic spot?
Impatiens necrotic spot is a viral disease that causes considerable losses to greenhouse-grown ornamentals and, to a lesser extent, vegetable crops. In the southern United States, impatiens necrotic spot can also be a problem on field crops. Ornamental crops affected by impatiens necrotic spot include impatiens, gloxinia, cineraria, cyclamen, exacum, petunia, begonia, primrose and ranunculus. Susceptible vegetables include cucumber, tomato and pepper. Impatiens necrotic spot also affects weeds including chickweed, jewelweed, oxalis, and gill-over-the-ground.
What does impatiens necrotic spot look like?
Symptoms vary from species to species and from cultivar to cultivar. Environmental conditions can also influence symptom development. Infected plants may exhibit chlorotic or necrotic spotting; stem, vein or growing point necrosis; ringspots, mosaic or line patterns on leaves; color break in flowers; wilting and collapse. Plants that are infected at a young age tend to exhibit more severe symptoms than those infected at an older age. Some plants may remain symptomless but still can be a source of the causal virus, leading to infection other plants.
Where does impatiens necrotic spot come from?
Impatiens necrotic spot is caused by the Impatiens necrotic spot virus (INSV). The primary means of plant-to-plant spread of INSV is by the western flower thrips (Frankliniella occidentalis). This insect acquires INSV when feeding on infected plant sap, carries the virus to its next feeding site, and transmits the virus to the new plant after 15 to 30 minutes of feeding. Only a few thrips are needed to spread INSV rapidly throughout a greenhouse. Numbers of INSV-infected plants also can be increased simply by taking vegetative cuttings from infected plants.
How do I save a plant with impatiens necrotic spot?
After infection, INSV spreads throughout a plant. Therefore plants remain infected indefinitely. Infected plants cannot be treated to remove the virus and should be destroyed by burning (where allowed by local ordinance), burying or composting.
Symptoms of impatiens necrotic spot on Gloxinia. (Photo courtesy of Margaret Daughtrey)
How do I control impatiens necrotic spot in the future?
Impatiens necrotic spot control focuses on excluding INSV and preventing its spread. Inspect any plants entering a greenhouse (e.g., new plant shipments, plants moved in from outdoors) for viral symptoms and thrips. Isolate new plants until they are determined to be thrips- and virus-free. In commercial settings, isolate breeding and stock plants from production, and do not carry over plants from fall production into the spring. Destroy any symptomatic plants. Control greenhouse weeds, which can be symptomless reservoirs of INSV. Monitor and control thrips populations. Exclude thrips by screening greenhouse vents and doors (screening should have apertures that are ≤0.135 mm). Set up yellow, white or blue sticky traps to monitor for thrips in growing areas and near greenhouse entry points. Indicator plants such as Petunia x hybrida ‘Summer Madness’, ‘Super Magic Coral’, or ‘Red Cloud’ (with flowers removed) can provide early warning signs of a problem with thrips. Petunia leaves on which INSV-free thrips feed will develop whitish feeding scars, while those leaves on which INSV-carrying thrips feed will develop small brown to black spots, turning tan with a dark border. See also University of Wisconsin Garden Facts XHT1022, Managing Thrips in Greenhouses, for additional pointers on thrips control, including insecticide recommendations.
For more information on impatiens necrotic spot:
Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
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 Tom German, Andy Witherell and Anna Whitfield for reviewing this document.
A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.qa.webhosting.cals.wisc.edu.
Authors: Amanda Gevens, UW-Madison Plant Pathology with contributions by UW-Madison Plant Pathology undergraduates Ken Cleveland and Lauren Thomas
Last Revised: 03/01/2024
D-number: D0062
Diseases of vegetable plants can pose a challenge for the home gardener. Typically, cultural methods are the preferred options for disease management in home vegetable gardens. Cultural methods include proper site selection, plant spacing, staking, watering, fertilization, and perhaps most importantly, use of disease-resistant vegetable cultivars. However, if diseases become especially problematic, fungicide treatments are also an option for home gardeners.
This guide is intended to help identify some of the common, and most suitable, fungicides available for disease control in home vegetable gardens. All of the fungicides listed on this fact sheet have been found on shelves at southern Wisconsin home garden centers. This listing is not intended to be exhaustive, but references fungicides that, when used properly, can be effective in controlling the most common diseases of vegetables grown in home gardens. When selecting a product from this list, be sure to note the product name carefully, as several products can have very similar names and contain similar active ingredients. Check that the active ingredient on the label of the product that you select is the ingredient that you are looking for. Also, 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.
VEGETABLE
DISEASE(S)
ACTIVE INGREDIENT
BRAND NAMES
asparagus
rust
chlorothalonil
Daconil, Fung-onil,
Ortho Max Disease Control
mancozeb
Mancozeb Flowable
myclobutanil
Spectracide Immunox
propiconazole
Monterey Fungi Fighter, Infuse
tebuconazole
Bayer Advanced 3 in 1,
Bayer Advanced Disease Control
bean
rust
chlorothalonil
Daconil, Fung-onil,
Ortho Max Disease Control
myclobutanil
Spectracide Immunox
propiconazole
Monterey Fungi Fighter, Infuse
tebuconazole
Bayer Advanced 3 in 1, Bayer Advanced Disease Control
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 Russell Groves, Stephen Jordan, James Kerns and Patti Nagai for reviewing this document.
A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.qa.webhosting.cals.wisc.edu.
Authors: Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 03/01/2024
D-number: D0060
What is herbicide damage?
Herbicide damage is any adverse, undesired effect on a plant that is caused by exposure of that plant to a pesticide designed for weed control (i.e., an herbicide). Any plant can be subject to this problem.
Squash leaf distorted due to exposure to a common lawn herbicide.
What does herbicide damage look like?
Symptoms of herbicide damage vary depending upon the plant affected and the herbicide used. Common symptoms include stems that are flattened, or that twist or corkscrew. Leaves may have abnormal shapes, sizes or textures. In addition, leaves or leaf veins may yellow or redden. In severe cases, plants may brown and die. Some plants, such as tomatoes and grapes, are particularly susceptible to herbicide damage and can be used as indicators of unwanted herbicide exposure.
How does herbicide damage occur?
Herbicide damage results when an herbicide is misapplied. Herbicides for control of broadleaf weeds are occasionally applied with fertilizers as part of a lawn care program. If these products are applied too close to ornamentals or vegetables, or are applied when there is too much wind, then the herbicide can drift (move) from the area of application into a non-treated area. Often, drifting herbicides are difficult to detect by eye because they are extremely fine mists. They can better be detected by smell. Some herbicides readily produce vapors that can begin to drift several hours after application.
How do I save a plant that has been damaged by herbicides?
There is nothing you can do after plants have been exposed. However, most plants accidentally exposed to broadleaf herbicides applied with lawn fertilizers do not receive a high enough dose to kill them. Young growth exposed to the herbicide will be distorted and discolored, but subsequent growth will be normal.
How do I avoid problems with herbicide damage in the future?
When using a lawn herbicide, follow the application directions exactly. DO NOT apply the product too close to, or in a manner that will cause exposure to, non-target ornamentals or vegetables. To avoid drift, apply the herbicide when there is as little wind as possible (< 5 mph). Apply the herbicide at low pressure to minimize production of fine mists. Finally, use amine forms rather than ester forms of herbicides as amine forms are less likely to produce vapors.
For more information on herbicide damage:
Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.
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 Sharon Morrisey, John Stier, Ann Wied and Chris Williamson for reviewing this document.
A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.qa.webhosting.cals.wisc.edu.
