Citrus Thrips Control Trial in California, 1987

Insecticides were evaluated for control of citrus thrips populations on 17-yr old Atwood Navel oranges located at the University of California’s Lindcove Field Station near Exeter, Calif. Pesticides were applied prebloom, petal fall (30 Apr), and/ or various dates after petal fall with a handgun set at 500 psi, outside coverage, and 200 gpa. The field was subdivided into 3 blocks with 1 replicate of each treatment within each block allocated randomly; each replicate consisted of 4 trees. The untreated control was replicated 10 times. Ten fruit per tree from knee to eye level were picked and sampled for citrus thrips infestation at weekly intervals for the critical 6 wk after petal fall during which citrus thrips fruit scarring occurs. Probably due to higher than normal temperatures in Apr, fruit set was very low (all 4 trees of 1 replicate in treatment 1 had only a few fruit and therefore were not sampled on +26 and +37 days so that sufficient fruit would remain for scarring counts). Citrus thrips fruit scarring counts were taken 1 month prior to harvest (on 13 Oct) on all fruit on the exterior of the tree from knee to eye level. Scarring was rated as: (a) none, (b) slight (any citrus thrips scarring), or (c) severe (complete ring scar or extensive surface scarring at a level that would cause downgrading of fruit in a commercial operation). Economic scarring levels in a normal year are approximately 5% severe scars.