Chemicals have limited effects on controlling it and there are no known resistant varieties of processing pumpkin to withstand an attack of the deadly blight known as Phytophthora capsici (P. capsici). Now, researchers at the University of Illinois suspect that rotating crops that are not susceptible to the disease may be a solution to the problem.

In a recent study, 45 species of crop and weed plants were screened for their susceptibility to P. capsici. Although 22 crop species succumbed to the disease, 14 did not. Mohammad Babadoost, plant pathologist at the University of Illinois in the College of Agricultural, Consumer and Environmental Sciences, believes that rotating the 14 resistant vegetable varieties may serve to wait out the pathogen until it is safe to once again plant pumpkins or other crops susceptible to P. capsici.

"Crop rotation is already being used by pumpkin growers as an important component of disease management," said Babadoost.  "Most pumpkin growers in Illinois follow at least a short-term crop rotation. However, most growers have experienced heavy losses when carrot, lima beans, pea, pepper, snap bean, and tomato were grown prior to pumpkin."

In order to make crop rotation a successful solution to waiting out the pathogen, a critical question remains to be answered: How long does the pathogen stay alive in the soil?

"Unfortunately, we don't know how long," Babadoost said. "Currently, I have a graduate student investigating that. We are trying to work out the problem piece by piece, then develop effective strategies to manage this disease. Definitely, the study that Tian completed provided us with very valuable information in dealing with this destructive pathogen."

Soybean, corn, and wheat, the major crops grown in Illinois, did not become infected, and there is no report indicating that these crops are hosts of P. capsici.  The other 11 vegetable crops that, when inoculated with P. capsici, did not develop symptoms of the disease are basil, broccoli, cabbage, cauliflower, celery, chive, dill, kale, kohlrabi, mustard and parsley. 

The 22 vegetable crop seedlings that became infected and developed symptoms of the disease in the study are: beet, carrot, eggplant, green bean, lima bean, radish, snow pea, spinach, Swiss-chard, tomato, turnip, onion, pepper and a long list of vine vegetables including pumpkin, cantaloupe, cucumber, gourd, honeydew melon, muskmelon, squash, watermelon and zucchini.

Babadoost said that the incidence of fruit rot on pumpkins caused by P.capsici has dramatically increased in Illinois causing yield losses of up to 100 percent. "Jack-o-lantern pumpkin is an important crop in Illinois, and approximately 90 percent of the commercial processing pumpkin produced in the United States are grown in Illinois, so this is an economic problem for the state."

Babadoost and crop sciences graduate student Donglan Tian completed the study which is published in the May 2004 issue of Plant Disease by the American Phytopathological Society.  The research was supported in part by funds from North Central Region Sustainable Agriculture, Research and Education, the Illinois Department of Agriculture and Nestle Food, Inc.