Perspectives Online

Disease forecasting helps growers avoid downy mildew

Ojiambo (left), Britton and Keever work together to develop the forecasting system.
Photo by Becky Kirkland

Just as weather forecasts help farmers plan their work, so, too, do modern plant disease forecasts. An N.C. State University-developed downy mildew forecasting system is helping cucurbit growers pinpoint times when conditions are most favorable for the disease to develop and, therefore, the best times to take action against it.

The Cucurbit Downy Mildew Forecasting Web site gives farmers and gardeners across the eastern half of the nation county-by-county information about active and potential disease outbreaks. That information is updated three times a week. The site also includes background information on downy mildew and how to identify and manage it.

Cucurbits are plants in the gourd family: watermelon, cucumber, cantaloupe, pumpkin and squash, to name a few. Downy mildew is one of the most serious diseases affecting these plants, causing severe problems to vines and leaves and reducing the size and number of fruit. The disease also reduces the sugar content of watermelon and cantaloupe, making them less marketable.

Before 2004, cucurbit downy mildew was not a major disease problem on cucumber in North Carolina, but that year there was a major outbreak on cucumbers that caused devastating losses. North Carolina is the second-leading state when it comes to cucumber production, and growers here hadn’t been using fungicides to protect their crops.

The forecasting project helps growers avoid financial losses caused by reduced yields and helps them avoid unnecessary — and costly — pesticide sprays, says Dr. Peter Ojiambo, the project leader and assistant professor in the Department of Plant Pathology.

Fungicides are more effective if growers apply them before infection starts, but applying them when there’s no threat isn’t cost effective, he adds.

The cucurbit downy mildew forecasting project got under way in 2008 with a $990,000 grant from the U.S. Department of Agriculture. The funding program is also known as the Pest Information Platform for Extension and Education, or PIPE.

In addition to Dr. Ojiambo, others involved in developing the forecast are Thomas Keever, the lead forecaster and meteorologist, and Wendy Britton, the project coordinator. The project involves 90 sentinel plots in 23 states as well as Ontario where extension plant pathology specialists from other universities monitor and report on downy mildew outbreaks.

Downy mildew is caused by a fungal-like micro-organism that spreads annually from south to north by airborne spores produced on infected plants. Knowing where outbreaks are located, Keever uses meteorological models to forecast where air from those locations is likely to travel over the next 48 hours and whether conditions are favorable there for disease development along the projected pathway. This gives farmers and gardeners time to apply fungicides ahead of time if needed.

The likelihood of downy mildew’s spreading depends heavily on weather conditions. Cloud cover shields airborne spores, allowing them to survive, but several hours of direct sunlight kills airborne spores.

Growers, crop consultants, extension agents, chemical company representatives and even some gardeners use the cucurbit downy mildew forecast at no cost. Beginning next spring, Web site users will be able sign up for customized email or text message alerts containing information on new infections and predicted risk for disease outbreak on their farms.

—Dee Shore