Insecticides Applied to the Soil for Control of Eight Species of Insects on Irish Potatoes in Virginia1

Abstract

Field experiments to control 8 species of insects were conducted on Irish potatoes in southeastern Virginia from 1961 to 1966. Twenty-five different compounds in several formulations, rates, and methods of application were evaluated as soil Insecticides. Applications of phorate, NIA 10242 (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate), disulfoton, Temik® (10% granular formulation of 2-methyl-2-(methylthio) propionaldehyde O -(methylcarbamoyl) oxime) and Dasanit ( O, O -diethyl O -[ p -(methylsulfinyl) phenyl] phosphorothioate) granules in the fertilizer band (2-3 pounds actual per acre) at planting gave highly significant reductions in Colorado potato beetle, Leptinotarsa decemlineata (Say), for 70-90 days. Band placement of the granules was superior to all other formulations and methods except dropping the granules directly in the seed furrow or use of insecticide-fertilizer combinations in bands. In general, the same insecticides and methods of application were most effective against potato flea beetles, Epitrix cucumeris (Harris), tobacco flea beetles, E. hirtipennis (Melsheimer), and potato leafhoppers, Empoasca fabae (Harris). Conversely, all were totally ineffective against the cabbage looper, Trichoplusia ni (Hubner). European corn borers, Ostrinia nubilalis (Hubner), were satisfactorily controlled by only 2 soil insecticides, Dasanit and NIA 10242, both of which reduced corn borer populations to negligible proportions. Foliage infestations of the potato tuberworm, Phthorimaea operculella (Zeller), proved to be somewhat more difficult to control but these 2 chemicals along with phorate gave best results. Later in the season Dasanit was superior to NIA 10242 and phorate. None of the soil systemics gave satisfactory reduction of black cutworm, Agrotis ipsilon (Hufnagel), damage to the tubers when used at practical rates. Likewise, dieldrin, chlordane, and diazinon, with only 65% reduction in damage, could not be regarded as satisfactory and were significantly less effective than foliage treatments with DDT, azinphosmethyl, or carbaryl, when these were timed to coincide with peak moth flights. Potato insect control resulted in consistent and often striking yield increases and improved quality as reflected by much higher specific gravities.