IMPACT OF INSECT FEEDING AND ECONOMICS OF SELECTED INSECTICIDES ON EARLY SUMMER BERMUDAGRASS SEED PRODUCTION IN THE DESERT SOUTHWEST

Bermudagrass seed yields were significantly increased by use of insect icides which controlled Trigonotylus tenuis (Reuter) (Hemiptera: Mirid ae) and Chirothrips spp. (Thysanoptera: Thripidae), although use of me thyl-ethyl parathion reduced yields. Seed yield differences among inse cticide treatments which controlled thrips (other than methyl-ethyl pa rathion) were highly correlated with adult T. tenuis numbers on last s ampling date (14 days) prior to harvest, which reduced seed yield by 2 2.1 kg/ha (19.7 Ibs/acre) per mirid/sweep. High numbers of T. tenuis w ere also highly correlated with reduced numbers of floral spikes, flor al spike height and blade height early in crop development. Cypermethr in was not as effective as other insecticides in controlling T. tenuis but did control Toya propinqua (Fieber) (Homoptera: Delphacidae). Toy a propinqua levels below 12.8/sweep did not cause sticky seed, and sho uld be considered in future integrated pest management decisions. Incr eased seed production offset insecticide cost except for the methyl-et hyl parathion treatment. Insecticide cost coupled with value of hay lo ss due to non-feeding restrictions with certain insecticides is calcul ated to be uneconomical in fields with yield potential less than 785.3 kg/ha (700 Ibs/acre) or when hay price is high. Changing insecticide use patterns and controlling T. tenuis could result in potential yield increases of 298.7 kg/ha (266.3 Ibs/acre), valued at over $2.0 millio n per year to bermudagrass seed industry.