RELATIONSHIPS AMONG EAR MORPHOLOGY, WESTERN FLOWER THRIPS, AND FUSARIUM EAR ROT OF CORN

The relationships among insects, corn (Zea mays) ear morphology, and ear rot caused by Fusarium moniliforme were studied in 1988 and 1989. Silks on ears of two corn hybrids, one susceptible to Fusarium ear rot and one with an intermediate level of resistance, received applications of the insecticides acephate or carbaryl at the green silk stage before the onset of ear rot symptoms. In both years, insecticide treatments reduced intra-ear populations of western flower thrips (Frankliniella occidentalis) at the brown silk stage and reduced disease incidence at maturity. In 1989, 15 corn hybrids, representing a range of susceptibility to Fusarium ear rot, were examined for ear morphology factors that may be correlated with disease incidence. Factors examined were heat units to silking; days from initial green silk to yellow-brown silk and to brown silk stages; intra-ear thrips populations at the green, yellow-brown, and brown silk stages; and husk looseness at the yellow-brown and brown silk stages. Disease incidence was correlated with thrips populations at the brown silk stage and with husk looseness at the brown silk stage but was not correlated with the other factors measured. Hybrids also could be separated by contrast analysis into susceptible, intermediate, and resistant groups on the basis of thrips populations and husk looseness at the brown silk stage. On the basis of these data, intra-ear thrips populations and husk tightness at the brown silk stage are important in the epidemiology of Fusarium ear rot.