Disease Note.

Severe Stewart’s Wilt in Central Illinois on Sweet Corn Hybrids Moderately Resistant to Erwinia stewartii. . J. K. Pataky, Department of Crop Sciences, University of Illinois, Urbana 61801 . L. J. du Toit Department of Crop Sciences, University of Illinois, Urbana 61801 T. E. Kunkel and R. A. Schmitt, Del Monte Corp., PO Box 89, Rochelle, IL 61801, and 205 N. Wiget Lane, Walnut Creek, CA 94598-2458. Plant Dis. 80:104. Accepted for publication 14 November 1995. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0104B.

Sweet corn (Zea mays L.) hybrids moderately resistant to Erwinia stewartii in previous trials (2) were severely infected under extreme Stewart’s wilt pressure associated with an abundance of corn flea beetles during hot, dry weather in central Illinois. Twenty-six fields of processing sweet corn planted from 26 June to 14 July 1995 in Mason and Tazewell counties were inspected in early August. Main stalks of severely infected plants were dead, tillers were growing profusely, and plants were barren. Leaf symptoms on plants with normal stalks and on tillers of plants with dead stalks were typical of resistant reactions, i.e., water-soaked lesions restricted to 1 to 2 cm from flea beetle feeding wounds. Symptoms of systemic infection (i.e., water-soaked, chlorotic, or necrotic streaks with wavy margins following veins of leaves) were sporadic. Hence, resistance appeared to be effective against the leaf blight phase of Stewart’s wilt. Incidence of main stalk death ranged from 5 to 50% in the 26 fields of commercial hybrids GH 2628 and Tribune. In early August, these fields had 10 to 20 flea beetles per plant, which was comparable with beetle populations in other central Illinois corn fields in early July. Therefore, we believe the high incidence of death of main stalks was associated with excessive flea beetle feeding when plants were emerging. Resistance, which restricts the movement of E. stewartii (1), may not have been effective if inoculum was introduced close to the plant’s growing point at a very early growth stage. In previous trials (2), pin-prick inoculation of sweet corn prior to the three-leaf growth stage occasionally killed main stalks. This is the first report of which we are aware of a case in which the natural occurrence of Stewart’s wilt caused a high incidence of main stalk death in several hundred acres of moderately resistant sweet corn hybrids.