Flea beetles and aphids: an update

摘要

The casual pathogen of Stewart's wilt in sweet corn is Erwinia stewartii, and it is vectored by the corn flea beetle. These small black beetles, 1/16-in. in length, overwinter in the ground as adults and appear on the earlier plantings from the seedling stage onward. Their feeding marks appear as narrow pinstripes 1/4 to 1/2-inch in length, parallel to the leaf veins. A proportion of the beetles retain the Stewart's wilt pathogen in their gut and vector the pathogen to sweet corn when they infest fields. Secondary infection and spread of the disease occurs as beetles feed on infected corn plants and disperse throughout the field. Yellow to brown stripes or streaks with wavy or irregular margins on leaves signal Stewart's wilt. Younger corn is more susceptible to the wilt than older plants, making time of infestation by corn flea beetle an important factor. Once corn is knee high or higher, Stewart's wilt will have only minimal impact. The bacterial pathogen multiplies in the vascular tissue, restricting flow of nutrients and moisture. Depending on the severity of the disease, yield and quality can be affected or the plant can be killed.