Status of the European Corn Borer in the United States in 1924

Abstract

During 1924 the European com borer, Pyrausta nubilalis Hubn., increased the area of its distribution in the United States from 16,052 square miles to 24,773 square miles. The greater part of this dispersion occurred in the stragetic area west and south of Lake Eric and advanced the pest well into the heavy com producing regions. In Ohio and Michigan there occurred an increase in intensity of infestation amounting to approximately 258 per cent and in western New York an increase in intensity of approximately 284 per cent. A decrease in intensity of approximately 20per cent occurred in New England. No increase of territory in eastern New York nor in the main New England area. The increases in the single generation western areas are believed to be char gable to favorable weather conditions while the decrease in the two generation area of New England is probably chargeable to the culminative effect of unfavorable weather conditions existing in 1923 and 1924 plus the very thorough dean up and plowing operations under the stimulus of the 'Massachusetts state law. Insectary experiments and field observations in Ohio indicated a larval survival of 10 per cent, based upon number of eggs deposited. The necessity of cutting com as low, and as early in the season as possible, was forcibly demonstrated by observations showing that the percentage of larval population, left in 6 inch stubble from stalks cut during early November was three times greater than in stubble of the same height cut during mid-September. Varieties of com characterized by large stalks and ears have exhibited a greater resistance to severe injury by the corn borer than varieties possessing small stalks and ears. None of the varieties tested to date possessed practical immunity from attack. In Ohio and Michigan the percentage of stalk infestation in sweet corn was slight1y greater than in field (dent) corn while the larval population in sweet corn was more than double that in field corn. In this same area but very little injury developed in fields of sweet or field corn planted after the first week of June. Early sweet corn as a trap crop failed to function under 1924 conditions. Clean plowing, especially during the late autumn, is recommended for infested crop residues which arc impractical to eliminate by burning or feeding. Two per cent free nicotine dust gave encouraging results during 1924 when applied at the period of maximum egg batching. A total of 1,168,276 foreign parasites, consisting of seven different species, have been liberated in the United Slates. Two of these species have been recovered in the field. European observations during 1924 showed that the corn borer is a pest of prime importance in the principal corn growing region of Hungary, where conditions are similar to those existing in the Corn Belt of the United States.