ABSTRACT

Field studies were initiated in cotton in the San Joaquin Valley of California to evaluate the impact of different amounts of leaf loss on growth and yield when the losses were concentrated in the first seven leaves of developing cotton plants. Evaluations were made over multiple growing seasons in field trials based on two approaches to looking at responses to leaf loss: (1) physical removal of specific main stem leaves at certain growth stages using a razor blade; and (2) measured leaf area loss produced using different rates and timing of insecticide applications to provide partial or more complete control of the thrips. Worm damage in any of the plants during the season was very light, particularly during early season growth, and the presence of thrips was confirmed visually and by field sampling. Other insect pests were controlled during the course of the growing season in all plots according to University of CA sampling guidelines, and kept below threshold levels in plots. Leaf removal treatments were 0, 29, 43, 57, 71 and 86 percent removal of the first seven main stem leaves on developing plants (with specific patterns and timing of leaf removal). Leaf area loss treatments produced using variable insecticide timing and rates produced leaf area losses ranging from 0 to 84 percent leaf area reduction as measured when the 7^th leaf reached 25 mm diameter in the 0 percent leaf loss control treatment. Early season leaf loss up to about 60 percent had no significant impact on lint yields. Leaf loss in the 77 and 86 percent treatments resulted in 6 to 16 percent reductions in final plant leaf area (measured in August), moderate delays (3 to 7 days) in reaching boll maturity (defined as 60% open bolls) and 9 to 16 percent reductions in yield.