Pest intensity-crop loss relationships for the leafminer fly Liriomyza huidobrensis (Blanchard) in different potato (Solanum tuberosum L.) varieties

Quantifying the relationship between plant injury and yield loss is a critical component for decision making in integrated pest management (IPM). The effects of foliar injury during different growth stages of potato (Solanum tuberosum L.), caused by natural populations of the leafminer fly Liriomyza huidobrensis (Blanchard) on potato yield, and the economic injury level for potato varieties with different maturity times were studied in the Cañete valley on the central coast of Peru. Field experiments were carried out during the potato cropping season (July–November) in the years 2005, 2007 and 2008 using early, middle-late and late potato varieties. Insecticides with different control efficiencies or the use of varying numbers of insecticide applications obtained various levels of leafminer fly infestation intensities. Leafminer fly infestation caused foliar injury in all potato varieties resulting in yield losses, which varied, according to the seasonal adult flight activity in each year of evaluation, between 22% in 2007 (2508 adults/trap/season) and 51% in 2005 (3147 adults/trap/season). Foliar injury increased with the development and growth of the potato plant, with the highest injury registered at the end of the cropping period. Early varieties showed higher foliar injury and yield loss than late potato varieties with the exception of Maria Tambeña, which is considered partially resistant to leafminer fly infestation. Yield losses increased linearly by each percentage of foliar injury in all potato varieties. Critical point and multiple point models made it possible to identify the potato growth stage at which leafminer infestation had the greatest effect on yield. Pest infestation-crop loss relationships indicated that the accumulated foliar injury up to the growth stages of flowering and berry formation produced the highest yield losses in the different potato varieties. Economic injury levels varied according to control costs and commodity values in each potato variety (Desiree: 21–28%, Revolucion: 34–47%, Canchan: 31–40%, Maria Tambeña: 40–53%, Tomasa: 55–74%, and Yungay: 40–54% of foliar injury). Potato varieties can tolerate considerable levels of foliar injury by the leafminer fly before control measures are needed. The use of the economic injury levels is suggested as a decision support tool for managing the leafminer fly at reduced pest management costs.