The culprit, Phytophthora capsici, has become a threat to many crops nationwide. First detected in Illinois in the 1990s, it seriously threatened the production of pie-pumpkin production near Morton and forced pepper growers near Shawneetown to move into other fields. The loss of pumpkin crops would have dealt a serious economic blow to Illinois, the nation's leading pumpkin-producing state.
"There are approximately 20,000 acres of pumpkins grown each year in Illinois, 8,000 to 10,000 for processing and 10,000 to 12,000 acres for jack-o-lanterns," said Mohammad Babadoost, a professor in the department of crop sciences. Illinois growers account for 70 percent of all commercial-processing pumpkins in the nation.
"We are making progress," Babadoost said. "We have the disease contained. A walk through pumpkin fields in the Morton-Pekin area late last month showed that the disease is still there, but not spreading as it used to be doing."
Babadoost is studying both immediate and long-term strategies to fight the pathogen, which has struck pumpkins, cucumbers, eggplants, melons, peppers, squashes, tomatoes, watermelons and zucchinis with seedling death, foliar blight and fruit rot. Crop losses of 100 percent had been recorded in 1999 and 2000 in Illinois following periods of frequent and sometimes heavy rainfall. Without intervention, a crop can be lost in a week.
Babadoost reported on some of his work in the July issue of the journal HortScience and in a late July presentation to the American Phytopathological Society annual meeting in Milwaukee. Another paper has been accepted by the journal Plant Disease.
In 2000, Babadoost's team tested 14 fungicides before narrowing their choice to Acrobat MZ, with approval from the U.S. Environmental Protection Agency, for field experiments on pumpkins in 2001. While results were positive, they found MZ to be too costly. This year, they are using Acrobat 50WP alone, again with EPA approval, applying 6.4 ounces per acre where the fungus is spotted. Growers mix it with a copper compound.
At the APS meeting, Babadoost and postdoctoral associate Sayed Zahirul Islam reported that three of 56 varieties of peppers -- Emerald Isle, Paladin and Reinger -- are resistant to the pathogen in Illinois.
In HortScience, Babadoost, Islam and Y. Honda, a researcher at Japan's Shimane University, documented that starting peppers, pumpkins and tomatoes under red light in a greenhouse offers protection against P. capsici. Less than 36 percent of the plants exposed to the fungus after four weeks of red-light treatment became infected, while between 78 percent to 100 percent of control plants started under traditional white light died.
Peppers transplanted into the field after red-light treatment are showing resistance in ongoing tests near Shawneetown, Babadoost said. Pumpkin transplants in experimental fields near Pekin are being evaluated. If red-light treatment offers season-long protection, he said, chemical applications eventually might be unnecessary.
Using red light may not be readily agreeable to pumpkin growers, Babadoost said, because pumpkins traditionally are grown directly from seed in the field rather than started in a greenhouse, a change that would involve extra costs. However, red-light treatment for other cucurbit crops such as cucumbers, melons and squashes would be readily available.
Another long-term solution showing promise is the use of a fungicide on seeds. In their Plant Disease paper, Babadoost and Islam detail how the fungicide mefenoxam (Apron), when applied to seeds, offers systematic protection to pumpkin plants in early growth stages, delaying the development of Phytophthora disease.
Since Apron is already registered for use on cucurbit plants, pumpkin growers may choose to use it and later apply Acrobat, if necessary, on affected plants, he said.