The sun has just risen as Grower Brown sips a cup of coffee and plans his activities for the day. His crop of summer squash is coming along, but he's worried about a disease that caught him off guard last year. The disease was downy mildew and it struck suddenly, leaving about 50% of the leaves scorched, as if by flames or frost. He lost a sizable portion of his crop despite three fungicide applications. The problem was the timing of his applications. By the time his first spray was applied (the day after he detected the problem), the disease was well established.

This year, Grower Brown's early morning routine includes accessing the Internet to check on the weather and look at the latest cucurbit downy mildew forecast. The forecast shows that the disease has already been reported on cucurbits (i.e., members of the gourd family: cantaloupe, cucumber, pumpkin, squash, watermelon, etc.) in states to the south, but no reports have been made in his home state yet. However, today's atmospheric trajectory shows that spores from southern sources are likely to arrive within 36 to 48 hours and that cloudy weather and rain is likely at the same time. The forecast outlook states that the risk of disease development in his area is high. Knowing how destructive the disease was last year and considering the information in the forecast, Grower Brown is seriously considering his first fungicide application of the season.

This isn't a futuristic scenario, but something that is happening every day. For the second season, we are testing the merits of a new system for forecasting atmospheric movement of cucurbit downy mildew on a national scale. The Web site can be accessed at www.ces.ncsu.edu/depts/pp/cucurbit/. Forecasts are made twice per week and begin when the first source of the disease is reported (e.g., May 14, 1998 and March 2, 1999). In addition to the forecasts, the Web site contains a great deal of information about the biology of the disease, a practical guide to foliar disease identification of cucurbits (through color images and line drawings of microscopic spores), as well as current control recommendations for downy mildew.

While the method of forecasting this disease is new, the idea is not. In the 1940s, researchers in 11 Atlantic coastal states reported the spread of cucurbit downy mildew from Florida to Massachusetts (C.J. Nusbaum, 1944 and 1948). They understood then that the evidence, although circumstantial, suggested that downy mildew probably overwintered on cucurbits in frost-free areas in Florida. Therefore, each year the pathogen spread northward with the advancing season by means of wind-borne spores.

The difference between what Nusbaum and his colleagues were doing in the 1940s and what we are doing 50 years later is adding precision, speed, and availability to the forecasts. The added precision is the result of two improvements: 1) the use of meteorological models to actually track spore movement; and 2) a large network of collaborators who quickly report disease outbreaks. The added speed and availability are the result of advancements in modern communication technology, such as the Internet and cellular phones.

The ball gets rolling once the disease is identified in a cucurbit field. There are 40 representatives from 15 states cooperating on the project and more are being added all the time. These representatives are typically plant pathologists or horticulturists who work on cucurbit crops and are aware of disease outbreaks in their region. They are also qualified to give a positive diagnosis of the disease. Growers are also encouraged to report disease outbreaks, either by means of a state coordinator or directly to the Web site. In either case, a positive diagnosis of the disease must be made.

An outbreak is then reported by means of an electronic report form on the Web site. The form requests pertinent information regarding the inoculum source (i.e., location, crop, size of field, disease severity, etc.). Seconds after the submitter clicks on the "send" button, the report is received by the forecasting staff in the Department of Plant Pathology at North Carolina State University (NCSU). A forecast is then issued based on the information received.

Forecasts are typically made on Tuesdays and Thursdays of each week, but can fluctuate as conditions demand. Modern communication technology makes it possible to go from disease detection in the field to a forecast on the Web in just a few minutes.

The idea is simple. The diseased plants are producing spores. These spores are being liberated into the air above the diseased plants. We want to know where that air will be traveling over the next 48 hours. Meteorologists have been forecasting air movement for a very long time. Thomas Keever, an NCSU meteorologist and disease forecaster, takes the location of the spore source, feeds the information into the appropriate meteorological model, and produces a "trajectory" or pathway showing the direction and speed the air (and spores) will be traveling (see "Sample Forecast" on page 35.)

Along with the trajectory map, a weather forecast is made considering those factors affecting downy mildew development. The forecast includes the production of new spores, survivability of spores, the likelihood for spore deposition via rain washout, and whether conditions will be favorable for disease development at the target locations.

Utilizing the information provided by forecasts, cucurbit growers can make informed decisions about disease control options. By knowing the level of risk associated with disease outbreaks up to 48 hours in advance, growers can help reduce the unnecessary use of pesticides and add timing precision to those applied.

This project is an experiment in disease forecasting. We are testing the merits of this system. What we know about the disease and how it spreads indicates that it should work. But the key to the success of the experiment is getting timely and accurate data about when and where cucurbit downy mildew occurs, and the only way we can know this is to have people report it.

Growers, extension agents, and others are the eyes and ears of the forecasting network. The more people that report the information, the more useful the data and the better the experiment will be. Researchers, county extension agents, crop consultants, and growers are encouraged to report disease outbreaks via the Internet (www.ces.ncsu.edu/depts/pp/cucurbit/), e-mail ( gerald_holmes [at] ncsu [dot] edu or ce_main [at] ncsu [dot] edu ) or telephone (919-515-9779 or 919-515-6992). AVG