Stewart's Wilt - Environment

Environment

The number of flea beetles emerging in spring from hibernation depends on the severity of winter temperatures. Warm winter temperatures favor the survival of flea beetle vectors and increase the risk of Stewart’s disease. Low temperatures are highly unfavorable for beetle survival. The numbers of emerging adults can be estimated by calculating a winter temperature index by averaging the mean temperatures (expressed in °F) for December, January, and February. If the sum of the mean temperatures is 90°F or greater, the beetles will survive in high numbers and the disease risk is high; if the sum is between 85° and 90°, the risk is moderate to high; 80° to 85°, moderate to low; and a sum less than 80°F represents low risk.

Flea beetles do not survive in the northern half of Illinois due to low winter temperatures. Those found in late spring or summer have migrated from the south. Snow or other winter cover apparently has little effect in providing sufficient shelter to enhance survival of the overwintering flea beetles. Prolonged periods of wet summer weather are unfavorable for beetle multiplication and feeding, while dry weather is favorable. Consequently, although this disease has been found throughout the world, the bacterium has never survived and spread other than in North America. The reason for this is because the disease depends on where Chaetocnema pulicaria occur. In North America, Stewart’s wilt is found in the mid-Atlantic and the Ohio River Valley regions and in the southern portion of the Corn Belt. This region includes parts of Connecticut, Delaware, Illinois, Indiana, Iowa, Kentucky, Maryland, Missouri, New Jersey, New York, Ohio, Pennsylvania, Rhode Island, Virginia, and West Virginia. Stewart’s wilt can also be found in eastern and midwestern states and prtions of Canada, but this depends on whether or not the corn flea beetles survive the winters. Corn flea beetles can transmit the bacteria northward during the summer, but if the insect vectors cannot survive the harsh winter temperatures, then the bacteria cannot be spread. The toothed flea beetle, adult 12-spotted cucumber beetle, seed corn maggot, wheat wireworm, white grubs, and larvae of corn rootworms can also carry Pantoea stewartii from one plant to another during the summer. These pests cannot overwinter and transmit this disease.