Evaluation of Admire Soil Treatments on Colonization of Green Peach Aphid and Marketability of Lettuce

Admire (imidacloprid), applied as a soil treatment, protected lettuce plants from developing infestations of green peach aphid, Myzus persicae (Sulzer), for 60 -100 d after planting based on two small plot and two commercial field trials. Admire applied 7.6 an sub -seed furrow provided longer and more consistent protection from green peach aphid than treatments applied to the soil surface, as a side dress, or 15.2 an sub -seed furrow. Surface band applications of Admire provided inconsistent control probably because of inadequate hydrological incorporation into the soil. In small plot trials, effective control of aphids by Admire applied Z 6 an sub seed furrow resulted in greater than 90.0% marketable heads while the untreated plots contained 20.0% marketable heads. When used in a commercial setting, Admire applied 7.6 cm sub -seed furrow on leaf lettuce prevented aphid colonization (<3 aphids per plant) for approximately 100 d after planting, while the untreated and commercial standard treated areas contained 30.7 and 26.8 aphids per plant respectively at 100 d after planting. In addition, marketability of lettuce was greater in Admire treated plots. As a sub -seed furrow treatment, Admire provides a more suitable approach to aphid control than is currently available with foliar insecticides. Introduction Green peach aphid, Myzus persicae (Sulzer), is a common pest of iceberg lettuce, Lactuca sativa, in the western United States. This polyphagous aphid species causes economic damage to lettuce through direct injury, virus transmission, and contamination of heads (Blackman and Eastop 1984, Reid and Cuthbert 1977, Hinsch et al. 1991). Because most Western iceberg lettuce is packed in the field at harvest, it must be relatively free of contamination by aphids and other pests. Consequently, lettuce is routinely treated with insecticides throughout the season to prevent aphid colonization. Green peach aphids are presently controlled in lettuce with foliar applications of contact insecticides such as acephate, endosulfan and mevinphos (Minkenberg et al. 1993). Plant growth characteristics, insect behavior, and insecticide chemistry largely determine whether an insecticide application can effectively contact the target pest (van Emden et al. 1969, Reid and Cuthbert 1977). Iceburg lettuce grows as a rosette, and much of the lower foliage of the plant is sheltered from above by upper leaves. Green peach aphids prefer to feed on the underside of lower lettuce leaves and are protected from many foliar applied insecticides (Anonymous 1987). Consequently, once green peach aphid has successfully colonized the lower leaves, it is difficult to achieve adequate control. An effective systemic insecticide would alleviate many of the coverage problems associated with aphid control on lettuce. Imidacloprid (Admire 2F), a new chloronicotynal insecticide, has a wide range of activity against many economically important insect pests such as aphids, whiteflies and thrips (Dewar and Read 1990, Elbert et al. 1990, Mullins 1993, Pike et al. 1993). Because it has considerable systemic activity in the plant, Admire may be appropriate for soil application in some crops. However, unlike other systemics, Admire is relatively immobile in the soil and should be placed precisely where root uptake can occur (Mullins 1993). Therefore, performance of the compound may vary depending on the crop and method of application (Getting and Anderson 1990). As a seed