The effect of hybrid and planting date on yield losses by the corn ear insects Helicoverpa zea (Boddie) and Spodoptera frugiperda (J.E. Smith) was determined in northeastern México, from 2006 - 2009. Eight corn hybrids (white and yellow) were planted each year during early January, February and March. Regardless of year, hybrid, or planting date, the most abundant ear insect was H. zea (61 - 99%). Yield losses varied greatly according to year, hybrid and planting date, with a maximum of 596 kg/ha, equivalent to 10.6% of total yield. Regarding planting dates, yield losses were lower in February, greater in March, and intermediate in January, probably attributed to host plant availability for ear insects in the region. An average of 74% greater yield loss was observed in yellow hybrids as compared with white hybrids for all planting dates, probably because of a differential grain hardness and husk wrap. According to current local value of corn grain and cost of insecticide and aerial application, insecticide treatment of lepidopterans attacking corn ears would have not been justified during this study.
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Vol. 47 • No. 2