Mildew Control In Organic Cucurbits

Downy and powdery mildew on pumpkin leaves

Editor’s Note: McGrath is in the Department of Plant Pathology and Plant-Microbe Biology at Cornell University.

MANAGING diseases is an important component of successful production of melons, squashes, cucumbers, and other cucurbit crops for organic and conventional growers. Unfortunately, many diseases plague these crops. Two important diseases, powdery mildew and downy mildew, cannot be avoided because the pathogens produce wind-dispersed spores capable of moving long distances. Occurrence of other diseases is typically more variable, depending on the presence of the pathogen (many survive between crops) and favorability of conditions.

New management tools for organic growers include resistant varieties, biopesticides, and a spore exclusion tunnel. The list of melon varieties resistant to powdery mildew continues to grow. In addition, cucumber varieties with a new source of resistance to downy mildew are on the way.

Research in New York has shown that complete control of downy mildew can be achieved by growing cucumbers in low and high tunnels set up with a low-cost air filtration system with allergen filters to trap spores. The system was designed and tested by Lou Lego at his farm, Elderberry Pond Farm in Auburn, NY. He uses the cucurbit downy mildew forecast program on his farm, which can be accessed at http://cdm.ipmpipe.org, to decide when to turn on the system.

New Tools

Several new biopesticides are helping to manage soil-borne as well as foliar pathogens for growers producing organically as well as conventionally.

● Double Nickel 55 (Bacillus amyloliquefaciens strain D747) is labeled to apply to soil for damping-off and vine decline and to foliage for downy mildew, gummy stem blight, and powdery mildew.

● Serenade Soil (Bacillus subtilis strain QST 713) is a new formulation for soil application. This bacterium colonizes roots and produces compounds that affect pathogens directly and triggers metabolic pathways to activate the plant’s natural defenses and modulate growth. It is labeled for diseases caused by Rhizoctonia, Pythium, Fusarium, Verticillium, and Phytophthora.

● Regalia (5% extract of Reynoutria sachalinensis) is now labeled to permit application in transplant water or as a soil drench, which might be more effective than applying to foliage. The product boosts the plants’ natural defense mechanism against certain fungal and bacterial diseases and is labeled for Anthracnose, downy mildew, gummy stem blight, Phytophthora blight, and powdery mildew in cucurbits.

Powdery Mildew Control Options

This disease is managed with resistant varieties and fungicides. An integrated program with both management tools is needed to achieve effective control. Additionally it is more difficult for new pathogen races or strains to develop when an integrated program is used.

There are resistant varieties in most crop groups with new varieties released most years. With melons, first find out what races occur in the area from state Extension specialists. Melons with resistance to pathogen races 1 and 2 provided good suppression of powdery mildew? when evaluated on Long Island in 2012. Many types of resistant melons are now available.

Be sure to select squash and pumpkins with resistance from both parents (homozygous resistance), when possible. The term homozygous resistance is used in a few seed company catalogs whereas others use terms like “high resistance” and “intermediate resistance” to generally refer to homozygous and heterozygous resistance, respectively.

The degree of disease suppression obtained with a variety also depends on modifying genes present. Resistant squash and pumpkin varieties have not provided as effective control in recent years as before, but they remain an important tool. Plant breeders are actively searching for new sources of resistance to powdery mildew.

Powdery mildew can be managed more effectively with organic fungicides than downy mildew. Many different products are available for growers to chose from that contain a large diversity of active ingredients, including botanical oils (such as sesame, rosemary, and thyme oil), mineral oil, potassium bicarbonate, biocontrol organisms (such as Bacillus and Streptomyces species), a plant extract (giant knotweed), copper, and sulfur.

The Trouble With Downy

Downy mildew is primarily managed with fungicides. Resistance was the main tool for cucumbers until a new strain of the pathogen appeared.

Since 2004, varieties with this resistance, which include most hybrids, have provided some suppression of the new pathogen strains present, but substantially less than what was achieved against strains present before 2004. However, these resistant varieties are still considered a worthwhile component of an IPM program. Fortunately, cucumber varieties with new genes for resistance are being developed.

Topics: , ,

Leave a Reply

One comment on “Mildew Control In Organic Cucurbits

Cucurbits Stories
Amblyseius swirskii predatory mite feeding on a thrips
Cucurbits
December 17, 2015
Study: Mighty Mite Might Be Big Benefit For Florida Cucumber Crop
Researchers find predator potent in controlling thrips. Read More
Sakata donated pumpkins to a Washington zoo for animal feedings, toys for the animals, pumpkin carving, fall displays, and activities for children attending the celebration. 
Photo courtesy of Sakata Seed America
Cucurbits
November 23, 2015
Sakata Donates Pumpkins To Washington Zoo
The pumpkins were used for a variety of purposes including toys for the animals and pumpkin carving. Read More
These watermelons were on display at Bayer CropScience Vegetable Seeds' field day, which was held in Florida earlier this month.
Cucurbits
November 16, 2015
Watermelon Field Day Highlights 26 Varieties
Bayer CropScience Vegetable Seeds’ event showcases varieties for Florida. Read More
Melons
Cucurbits
November 15, 2015
Melon Genome Study Discloses Impacts Of Breeding
Analyses of seven melon varieties will help breeders increase plant quality. Read More
Arizona melon field
Crop Protection
November 10, 2015
Management Tactics To Control Cucurbit Yellow Stunting Disorder Virus
This virus, which was discovered in 2006, is transmitted by whiteflies and infects several melon types in Arizona and California. Read More
Goldprize zucchini
Cucurbits
October 28, 2015
7 Cutting-Edge Cucurbits Fitting For Florida Farmers
See the latest cucumber and squash selections from leading seed companies. Read More
Allsweet Seeded 800F1 watermelon
Cucurbits
October 26, 2015
19 Marvelous Melons Bred For Market Impact
Check out the latest watermelon and cantaloupe varieties from leading seed companies. Read More
The Latest
Cucurbits
January 27, 2016
Imported Cucumbers Connected With Multis…
Since the Salmonella outbreak occurred in September, nearly 900 people in 39 states have fallen ill. Read More
Cucurbits
January 20, 2016
9 Watermelon Varieties You Need To Know …
Check out these watermelon varieties boasting high Brix, a good disease resistance package, and excellent yield potential. Read More
Cucurbits
December 22, 2015
National Watermelon Association To Inaug…
Past leaders to be honored as the inaugural class of the association’s Hall of Fame. Read More
Cucurbits
December 17, 2015
Study: Mighty Mite Might Be Big Benefit …
Researchers find predator potent in controlling thrips. Read More
Cucurbits
November 23, 2015
Sakata Donates Pumpkins To Washington Zo…
The pumpkins were used for a variety of purposes including toys for the animals and pumpkin carving. Read More
Cucurbits
November 16, 2015
Watermelon Field Day Highlights 26 Varie…
Bayer CropScience Vegetable Seeds’ event showcases varieties for Florida. Read More
Cucurbits
November 15, 2015
Melon Genome Study Discloses Impacts Of …
Analyses of seven melon varieties will help breeders increase plant quality. Read More
Crop Protection
November 10, 2015
Management Tactics To Control Cucurbit Y…
This virus, which was discovered in 2006, is transmitted by whiteflies and infects several melon types in Arizona and California. Read More
Cucurbits
October 28, 2015
7 Cutting-Edge Cucurbits Fitting For Flo…
See the latest cucumber and squash selections from leading seed companies. Read More
Cucurbits
October 26, 2015
19 Marvelous Melons Bred For Market Impa…
Check out the latest watermelon and cantaloupe varieties from leading seed companies. Read More
Cucurbits
October 13, 2015
Researchers Find That Grafting Increases…
University of New Hampshire researchers aim to improve cold tolerance, disease resistance. Read More
Cucurbits
October 6, 2015
Bayer CropScience Vegetable Seeds, Natio…
Bayer to fund first-year memberships to all eligible watermelon growers. Read More
Cucurbits
August 31, 2015
8 Must-Have Melons
This month’s variety specs feature focuses on the latest cantaloupe and melon varieties. Some of the features highlighted include disease Read More
Cucurbits
July 22, 2015
Win The War Against Bacterial Wilt Of Cu…
Learn how to identify, the survival and spread, as well as management methods of this vegetable disease. Read More
Cucurbits
July 22, 2015
Sakata Promotes Melon With Long Shelf Li…
The variety Infinite Gold features good holding ability in the field. Read More
Cucurbits
July 14, 2015
High Heat Impacts Georgia Watermelons
Numbers are expected to be lower this year, but it is too early to tell by how much. Read More
Crop Protection
July 8, 2015
Downy Mildew Reported In Ohio Cucumber F…
According to a disease update from Ohio State University Extension, downy mildew was reported in cucumbers on farms in West Read More
Cucurbits
July 1, 2015
11 Pumpkin And Squash Varieties
This month’s variety specs feature focuses on pumpkin and squash varieties. Features highlighted include great disease resistance packages, excellent yield potential, Read More
[gravityform id="62" title="false" description="false"]