Image credit: Anthony P. Keinath, Clemson University. Fungicides are necessary to manage downy mildew on all cucurbits grown in South Carolina in summer and fall. pathogen produces microscopic sac-like structures called sporangia
Plant resistant varieties if youve struggled with this disease in the past. reduce humidity levels inside the crop canopy. Downy mildew infects gourds, squash, pumpkins, melons and cucumber. progresses, the lesions expand and multiply, causing the field to
Fortunately it has occurred sporadically in this region, usually appearing late enough in the growing season that yield is not impacted. *Note: 30-day pre-harvest interval on cantaloupe and 7-day pre-harvest interval on cucumber and squashes with Omega. Extension. They are also more likely to develop sun scald, which further reduces
To stick and work, fungicides must be dry on the leaves before rain starts. Crops planted as early as possible after the last predicted frost may not need to be treated with fungicides. the late morning to facilitate rapid leaf drying. Image credit: Anthony P. Keinath, Clemson University. Compare what you are seeing to other diseases like angular leaf spot and powdery mildew. Choose cucumber varieties with resistance to downy mildew; see the. During prolonged
the disease symptoms. The use of any brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by Clemson University nor does it imply discrimination against similar products or services not mentioned. The Cucurbit Downy Mildew Forecast
Evaluation of seeding dates and fungicide application to manage downy mildew on slicing cucumber, 2021. Consider irrigating during
Downy mildew spreads quickly on cucumber, cantaloupe, and watermelon. Cucumbers are the most susceptible crop to this pathogen. Toll Free: 1-877-424-1300
Downy mildew isnt seen in Minnesota most years. The downy mildew pathogen tends to be specific to crops
Figure 3. NC State University and NC For example, in squash before disease is reported in the state you can use: Presidio + Bravo, alternated with Zampro + Bravo, alternated with Tanos + Bravo every 10 days. Anthony P. Keinath, PhD, Professor of Plant Pathology,
Fungicides recommended to prevent and manage cucurbit downy mildew. In these areas, the inoculum
Killing frosts and cold winters
This downy growth is masses of pathogen spores called sporangia, which can be seen in the field with a 20X hand lens. periods, the disease may move onto the upper crop canopy. Downy mildew causes angular, yellow to brown lesions on top of the leaves that are restricted by leaf veins (Figure 1). Rain, dew, or fog makes infection likely. Apply fungicides before a predicted rain rather than after it rains. It occurs worldwide where conditions of temperature and humidity allow its establishment and can result in major losses to cucumber, melon, squash, pumpkin, watermelon, and other cucurbits. It requires
and rounder on infected watermelon leaves (Figure 6). often develop sun scald and are not marketable. Prevention before it appears, and prompt action afterward, are needed to manage this aggressive pathogen. of melon leaves appear irregular shaped. In the Midlands and Upstate, downy mildew usually appears after June 1. use trickle irrigation. Once the disease is reported in the state, using the highest rate labeled for products will result in better control and lower risk of fungicide resistance. hosts (wild cucumber, goldencreeper and volunteer cucumbers) in
transplants are at risk of developing downy mildew from wind-borne
Agrios, George N. 2005. This site is a project of the Cornell Vegetable Program Work Team (PWT). Cucurbit downy mildew survives over winter on crops growing in southern Florida and Texas where cucurbits do not freeze. Individuals who use agricultural chemicals are responsible for ensuring that their intended use of the chemical complies with current regulations and conforms to the product label. Downy mildew can begin to develop at any time during cucurbit crop development in the northeastern US. Fungicides are the main management practice. this disease. Cucurbit downy mildew is caused by the fungus-like oomycete pathogen Pseudoperonospora cubensis (P. cubensis). Yellow to pale green spots form on the upper side of the leaves, and on the underside, there is velvety grey fuzz. of the leaf. For the latest fungicide recommendations for cucurbit downy mildew see the Southeastern US Vegetable Crop Handbook. For Current information on disease recommendations ins specific crops including information on chemical control & pesticide management, please visit the New England Vegetable Management Guide website. Isolates belonging to clade 2 can quickly become resistant to fungicides, thus, fewer effective fungicides ara available for downy mildew control in cucumber and cantaloupe. In the spring, wind blows downy mildew spores northward from the South. 2022 However, in some seasons it can move up the eastern seaboard early and arrive in July. Greenhouse growers are strongly recommended to use there tolerant varieties since chemical control options in a greenhouse are very limited and the risk of fungicide resistance is very high. overhead irrigation, insects, tools, farm equipment, the clothing
Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. will promote disease development, especially when accompanied by
Tank mixing fungicides specific for downy mildew with protectant fungicide also helps prevent fungicide resistance. appear angular in shape (Figure 4). Compendium of Cucurbit Diseases. The progress of Downy mildew is tracked by the the Cucurbit Downy Mildew Alert System (http://cdm.ipmpipe.org/). Use plant spacings which reduce the density of the plant canopy. There are two main races, one that infects cucumbers and melons, and one that infects pumpkins and squash. These spores germinate to produce the pathogen and infect leaves. This factsheet was prepared by the NCSU Vegetable Pathology Lab in 2013 with funding provided by Pickle Packers International, Inc. Find more information at the following NC State Extension websites: Publication date: Dec. 16, 2018 Sporangia (spore sacks) in the lesions
1996. Clemson (SC): Clemson Cooperative Extension, Land-Grant Press by Clemson Extension; 2022 May. Physiological specialization occurs in P. cubensis and at least five pathotypes have been described. Figure 7. High pressure (at least 75 psi) and high volume (at least 75 gpa) are needed once vines touch. Regents of the University of Minnesota. About
In eastern states with similar conditions, downy mildew does not arrive until the end of the growing season, often in August. For more information:
Downy mildew is a serious disease of cucurbit crops grown in Ontario
Keinath AP, Miller SA, Smart CD. On most species, lesions are first visible on the upper leaf surface as small, irregular to angular, slightly chlorotic areas. Figure 6. many zoospores. infected with downy mildew eventually turn brown and curl giving
Symptoms of downy mildew are confined to the leaves and their appearance varies widely among cucurbit species. Contact the State Center Directors Office if you have concerns related to discrimination, 413-545-4800 or see ag.umass.edu/civil-rights-information. Some resistant varieties are available for pumpkins and winter squash, but this is usually specific to certain variants of downy mildew and may not be effective in all cases. Both these practices are aimed at minimizing the length of leaf wetness periods. 2005. The
For downy mildew to occur in Minnesota, air currents must blow the spores from the South where it overwinters. Figure 3. Figure 2. date for this page, please contact the webmaster at -internet.webmaster.omafra@ontario.ca. Consult. Maximum control can be achieved only with a combination of these measures. movement of the disease throughout the growing season and make timely
Squash and pumpkin cultivars are resistant to some pathotypes but are very susceptible to compatible pathotypes. p. 7. Scout fields for symptoms of the disease every week - more often
The Center for Agriculture, Food and the Environment and UMass Extension are equal opportunity providers and employers, United States Department of Agriculture cooperating. Use program 1 in table 1 to prevent downy mildew. For pickling cucumber the varieties Citadel and Peacemaker from Seminis are tolerant to clade 2 isolates causing cucumber downy mildew. Once the disease is reported in the state, using the highest rate labeled for products will result in better control and lower risk of fungicide resistance. If you
There are two types of P. cubensis isolates that can infect cucurbit crops and weeds referred to as clade 1 or clade 2 isolates. Follow a preventative spray program. Plant early in the season to escape high disease pressure, Do not allow water to remain on leaves for long periods of time, Scout plants often and remove infected plants. Pathogen sporulation is below the yellow and brown symptoms visible on the upper surface (first image). In organic production, fixed copper fungicides help to prevent cucurbit downy mildew, but only if they are applied before infection. Inspect crops weekly for symptoms and have suspect samples confirmed by an extension specialist. Regularly check the UMass Vegetable website (http://ag.umass.edu/vegetable) or Cucurbit Downy Mildew Alert System (http://cdm.ipmpipe.org) for information about Downy mildew occurrence, forecasts, and risks of disease development. E-mail: ag.info.omafra@ontario.ca, Accessing this message means you do not have a JavaScript enabled browser. sacks) that can be observed with a hand lens (Figure 7). of workers and through the handling of infected plants. Downy mildew is often confused with other foliar diseases such as: Figure 3. infections on cucurbits produce more sporangia within 4 days. if possible. Most cucumber varieties commercially available are resistant to P. cubensis clade 1 isolates but there is no resistance available for clade 2 isolates. heavy dews, fog or precipitation. Because rain favors this disease, when possible protect crops before and after a rain event. Research and Extension Vegetable Pathologist,
Sporangia are
Fruit of infected plants are usually undersized and misshapen. When planting cucurbit transplants, ensure that the transplants
LGP 1019. http://lgpress.clemson.edu/publication/powdery-mildew-on-watermelon. With nighttime temperatures around
Pale green to yellow spots form on the upper surface of leaves, and later turn brown. Table 1. Due to the rapid spread of this disease and because symptoms often
pp. For pickling cucumber the varieties Citadel and Peacemaker from Seminis are tolerant to cucumber downy mildew. Vegetable Crop Handbook (vegcrophandbook.com).3. Trellising does not help manage downy mildew.4. The pathogen comes into our area on air currents from the south, but many years it never makes it to Minnesota. This Factsheet was written by Michael Celetti,
For slicing cucumber the varieties SV3462CS and SV4142CL. It is caused by the fungus-like water mould Pseudoperonospora
the plant a brown crispy appearance. If possible,
Extensive defoliation can occur when conditions are favorable. This publication printed on: July 29, 2022, Skip to Favorable Environmental Conditions for the Disease, Skip to Disease Control for Conventional Growers, Skip to Disease Control for Organic Growers, Skip to Disease Control for Home Gardeners, NC State Extension Plant Pathology portal, NC on the underside of the light yellow lesions observed on the top
Apply broad-spectrum protective fungicides before detection and systemic narrow-spectrum fungicides when downy mildew occurs early in crop production. Leaf spots on cucumber (figure 1) or cantaloupe start as pale green to yellow, angular spots that turn brown. Organic growers have less chemical options that are effective; the only OMRI labeled active ingredients that have some efficacy against cucurbit downy mildew are fixed copper formulations. N.C. carried long distances by storms and may survive for several days. Trellis plants to improve air circulation. Cucurbit downy mildew can also be spread through diseased transplants. Published: May 9, 2022 | Printable Version (PDF) | Anthony P. KeinathLGP 1002. Sometimes spots are small and yellow (figure 3), and in other cases, they are up to one-half inch wide, irregular, and brown. Figure 1. different strains (pathotypes) of this organism have been identified
The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by NC State University or N.C. A&T State University nor discrimination against similar products or services not mentioned. on the underside leaf surface appear as black specks. builds up on susceptible hosts in the early spring. Zitter, Thomas A., Donald L. Hopkins and Claude E. Thomas. The Cucurbit Downy Mildew Forecast map (cdm.ipmpipe.org) shows where downy mildew has been reported in the current year. Contact your local Extension office for information on disability accommodations. Listen to Meg McGrath talk about managing downy mildew in a teleconference hosted by Steve Bogash ofMarrone Bio Innovations on 17 June 2020. Figure 4. The information in this publication is provided for educational and informational purposes only. Dr. Lina Quesada, NC State Vegetable Pathology Lab. Individuals who use agricultural chemicals are responsible for ensuring that their intended use of the chemical complies with current regulations and conforms to the product label. do not appear until 4-12 days after infection, a successful disease
Downy mildew does not create viable oospores (thick-walled resting structures) that would allow it to survive outdoors during Minnesota's harsh winter. Contact. Authors: Marissa Schuh, horticultural IPM extension educator, and Michelle Grabowski, Reviewed by Natalie Hoidal, Extension educator. Kemble JM, senior editor. Revised: Jan. 5, 2021, There is an alternate Spanish language version of this document here: Aublo lanoso en cucurbitceas. The information in this publication is provided for educational and informational purposes only. Keinath AP. New England Vegetable Management Guide website. Spread of Downy mildew within a field can be by air currents, rain splash, workers, and tools. After disease is reported in the state you can use: Ranman + Bravo, alternated with Previcur Flex + Bravo, alternated with Orondis Opti every 5 to 7 days, with the shorter interval if the weather is wet and cool. When conditions (leaf wetness and humidity) favor sporulation, the production of fruiting bodies (sporangia) on the lower leaf surface gives the undersides of the lesions a downy appearance, varying in color from light gray to deep purple. Clade-specific biosurveillance of. This disease may progress slowly or stop temporarily when temperatures
and Elaine Roddy, Vegetable Crops Specialist, OMAFRA, Ridgetown. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. The site also predicts where spores will spread from known sources and where weather will be favorable for a new outbreak in the next 48 to 72 hours. cucurbits will not infect legumes or spinach and vice versa. Because rain favors this disease, when possible protect crops before and after a rain event. rise above 30C during the day. Receive Email Notifications for New Publications. Downy mildew on the bottom of infected leaves. Check label for restrictions of number of applications to plan your program. 2022. Nighttime temperatures of 12C-23C
appear smaller and rounder than on cucumber or cantaloupe leaves. Along the coast of South Carolina, cucurbit downy mildew usually shows up after May 1. such as soft rot bacteria or other fungi. 2022 University of Massachusetts Amherst Site Policies, Center for Agriculture, Food,andtheEnvironment, Request a Crop & Pest Management Planning Meeting, Northeast Vegetable and Strawberry Pest Identification Guide, Cucurbit Disease Scouting & Management Guide, Sweet Corn IPM Scouting Guide & Record Keeping Book, Nutrient Management Guide for New England Vegetable Production, Heating Greenhouses with Locally Grown Corn, Recursos en Espaol (Spanish-Language Resources), http://vegetablemdonline.ppath.cornell.edu/Tables/TableList.htm. Cooperative Extension prohibits discrimination and harassment regardless of age, color, disability, family and marital status, gender identity, national origin, political beliefs, race, religion, sex (including pregnancy), sexual orientation and veteran status. Recommendations for the use of agricultural chemicals may be included in this publication as a convenience to the reader. fungicide applications: Monitor the Cucurbit Downy Mildew Forecast website to follow the
Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. Cucurbit crops such as cucumber, watermelon, melon, cantaloupe, squash, and pumpkin. Margaret Tuttle McGrathAssociate ProfessorLong Island Horticultural Research and Extension Center (LIHREC)Plant Pathology and Plant-Microbe Biology SectionSchool of Integrative Plant ScienceCollege of Agriculture and Life SciencesCornell Universitymtm3@cornell.edu. Symptoms of downy mildew lower surface of cucumber leaf. sources early in the spring, before the field crop has been planted. Outbreaks of cucurbit downy mildew are most likely to occur during mild, wet weather. Orondis fungicides may be sprayed twice if the total number of sprays is six to eight. neighbouring fence rows and field edges. Maximize the distance between cucurbit fields to limit potential inoculum sources. of Cucurbit Diseases: Observations, Identification and Control. There are resistance concerns around downy mildew, so make sure to follow labels carefully and rotate products. LGP 1001. http://lgpress.clemson.edu/publication/watermelon-fungicide-guide. Rural
Moderate to low levels of resistance are available for melons. dew formation. Downy mildew on cucumber leaf. The main means of control are fungicide applications, the use of resistant cultivars, and cultural practices. Alternaria leaf blight on watermelon. Orondis Ultra (Orondis + Revus premix) is not recommended on cucumber, cantaloupe, or honeydew, because strain 2 is insensitive to the Revus component (table 2).6. A preventive spray program with chlorothalonil or mancozeb will give you a head start before downy mildew spores blow into the area. Once the disease arrives in Ontario and becomes established in a
cool wet periods, the sporangia can also burst open and release
Avoid excess overhead irrigation. Consider washing equipment and tools before moving from one
Strain 1 found in Charleston, South Carolina, in 2020 and 2021 is less sensitive to Orondis than it was in 2015.6 Orondis products must be rotated with other fungicides recommended for downy mildew to lower the risk of resistance getting worse. Under humid conditions, downy mildew rapidly reproduces and spreads, resulting in severe crop damage. Plant cucurbits as early as possible. Cucurbit leaves form a very dense canopy. For assistance, contact your local N.C. News
Downy mildew primarily overwinters in the southern U.S. and Mexico
Strain 1 mainly attacks watermelon, pumpkin, and squashes. The pathogen can move on air currents, splashing water and on the tools and hands of growers. It cannot survive on plant debris and only grows on living plant tissue. In a fungicide program, Orondis fungicides must be rotated with two other fungicides 1:1:1. The downy mildew pathogen primarily infects the leaves, resulting
and can directly infect the leaf within one hour. There are no effective pesticide products for downy mildew available to home gardeners. Spores come to North Carolina every year from infected plants in surrounding states or in greenhouses with year-round production. Bertucci M, Jennings KM, Meadows IM, Rodrigues C, Walgenbach JF, Wszelaki AL, associate editors. The sporangia act similar to spores. Read our Babadoost, Mohammad, Richard A. Weinzierl, John B. Masiunas. growing season and alerts growers to the potential movement of the
mornings after a period of wet weather or when conditions favour
Before disease appears apply fungicides at 7-day interval for cucumbers and 10-day intervals for other cucurbits. fungicide applications. Unmanaged gardens can become a source of inoculum for commercial plantings, thus, it is important that home owners are actively scouting their plants for downy mildew. Alternate products and tank mix with mancozeb or chlorothalonil to avoid generating fungicide-resistant strains. Image credit: Anthony P. Keinath, Clemson University. 6 hours of high humidity. The downy mildew pathogen is an obligate parasite. As the disease
is a web-based downy mildew forecasting system that follows the
Do not rotate Orondis Opti and Orondis Ultra with each other. 427-33. are free from disease. Figure 2. Manage. The yellow spots sometimes take on a "greasy"
Plant Dis. Interaction of cucurbit host with different
(Table 1). Ensure field workers wash their hands before moving from one
Unprotected cucumber fruit
Civil Rights and Non-Discrimination Information, UMass Research and Education Center Farms, Soil and Plant Nutrient Testing Laboratory, Water Testing / Environmental Analysis Laboratory, Conservation Assessment Prioritization System (CAPS), Extension Risk Management/Crop Insurance Education, North American Aquatic Connectivity Collaborative, Agriculture & Commercial Horticulture Resources. the topside of leaves (left) are often the first symptom of downy
All rights reserved. Summer squash, zucchini, and acorn squash tolerate some downy mildew. cubensis. Special notes about Foliar Orondis products. Downy mildew is favoured by cool, wet and humid conditions. 3rd ed. right). of the downy growth on the underside of the lesion is a key to diagnosing
biens fonds agricoles, Agricultural Information Contact Centre 1-877-424-1300. Many commercial cultivars of cucumber have good levels of resistance to Downy Mildew. 2022 Southeast U.S. vegetable crop handbook. This means it is possible to see a healthy pumpkin field alongside a severely diseased cucumber field. The authors would like to acknowledge Dr. Ron Pitblado for his contributions
Keinath AP. in the same greenhouse as mature greenhouse cucumber plants. This web resource is designed to enhance access to Cornell's vegetable production resources. This downy growth is particularly noticeable in the
movement of downy mildew from the south to north throughout the
Request a Crop & Pest Management Planning Session, CenterforAgriculture, Food, and theEnvironment, Center for Agriculture, Food and the Environment, Monitor disease occurrence and weather forecasts at. Check label for restrictions of number of applications to plan your program. appear irregular shaped (Figure 5), whereas the lesions are smaller
In wet or very humid conditions, the disease develops rapidly. a row cover or tunnel and immediately after the row cover or tunnel
take on a brown and "crispy" appearance. field to another and, if possible, wear freshly laundered clothing
The pathogen that causes downy mildew in
A&T State University. APS Press. Rahman A, Standish JR, DArcangelo KN, and Quesada-Ocampo LM. Several
(Figure 1). In most parts of the United States, both strains 1 and 2 of cucurbit downy mildew are resistant to Ridomil, Forum, and FRAC Group 11 fungicides (Cabrio, Quadris, Flint, Pristine, and Reason).5 Resistance to Previcur Flex, Tanos, and Curzate is also present in some strains and locations, so these fungicides are not recommended against cucurbit downy mildew in South Carolina. management program must be implemented prior to the appearance of
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