Influence of Planting Date and Insecticidal Control on Seasonal Abundance of Lettuce Aphids on Head Lettuce

Abstract

Small plot studies were conducted from 1999-2001 to examine the population abundance and control of the lettuce aphid on winter and spring head lettuce crops. In each year, Seven, 0.25 acre planting of head lettuce were established beginning in Sep-Oct with final harvest occurring in April. Replicated plots within several planting were treated with an Admire treatment at planting, a side dress application of Platinum post-planting or allowed to remain untreated. Lettuce aphids were first detected in our experimental area in December in PD 3 in 2001, but in 2002 first occurred in lettuce almost 2 months later (Feb 21). Similarly, lettuce aphid abundance was much greater in 2001 than in 2002, probably a result of temperature difference. Temperature had an important influence upon lettuce aphid development based on our field observations. Population appeared to increase in early March when the average daily temperature was about 65 E F. We observed a sharp decline in population abundance in April where daytime highs exceeded 90E F. Insecticide treatments also influenced seasonal abundance. Under heavy aphid pressure in 2001, lettuce treated with Admire in the early planting dates appeared to prevent lettuce aphids from significantly infesting lettuce heads at harvest. However, lettuce aphids in the last 3 planting dates were able to colonize plants and infest a larger proportion of heads at levels not considered commercially acceptable. Under lighter pressure in 2002, lettuce aphids did not significantly colonize Admire treated lettuce. Green peach aphid, potato aphid and foxglove aphids were also present in both years, but seldom reached economic levels, and where completely controlled in plots treated with soil, systemic insecticides.