Problems in the Control of Mint Insects1

Abstract

Of the 54 species of insects and related pests found on peppermint and spearmint in Indiana, only cutworms and the mint looper, Raphoplusia ou (Gn.), have been serious problems in the past 10 years. The mint flea beetle, Longitarsus waterhousei Kut., has not been abundant since growers adopted a 2-year crop rotation for mint. Several species of leafhoppers and plant bugs have been present every year, but losses from their feeding have been slight. Cutworms were present in mint fields both early in the season and again near harvest. Chlordane, aldrin, dieldrin, and heptachlor gave good control of these pests when applied in late April and early May as the first new growth was appearing. Cutworms present in July and August were controlled by a single application after the crop was cut The mint looper was found to have two generations a year with the peaks of larval abundance in late June and again in mid- August. Of numerous insecticides tested against the looper, dieldrin, heptachlor, and DDT were the best. Two applications at a 10-day interval in late June gave excellent control. Malathion was found to be of value against spider mites and to some extent against plant bugs and leafhoppers. Of the materials used as foliar sprays only malathion has had a tolerance established and usage labels approved. Apparent residues found in mint oil from heptachlor- and dieldrin-treated plots were quite variable in different years and in some instances were as high as 2.7 and 4.7 p.p.m., respectively. Methods of analyzing for residues in mint oil, especially for dieldrin, toxaphene, and DDT, have not been satisfactory. DDT, however, has been the standard treatment for mint insects since 1947. The use of insecticides on mint foliage created another problem-that of possible off-flavor in the oil. Oil samples from treated plots were sent to company experts for flavor evaluation and the following materials were approved for use: DDT, dieldrin, chlordane, heptachlor, toxaphene, Strobane® (a terpene polychlorinate with a chlorine content of approximately 66%), malathion, parathion, EPN-300, and Chlorthion® ( O -(3-chloro- 4-nitrophenyl) O,O -dimethyl phosphorothioate). Two materials, aldrin and lindane, were listed as questionable, whereas BHC was objectionable.