Development of economic thresholds and monitoring systems for Helicoverpa armigera (Lepidoptera: Noctuidae) in tomatoes.

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Field sampling methods and economic thresholds were developed to provide management recommendations for Helicoverpa armigera (Hübner) on processing tomatoes, based on a commercially acceptable damage level of 5% fruit damage. Population estimates from destructive sampling and a rapid 1-min plant scouting method were related to fruit damage, and a nominal economic threshold of one larva per plant was derived. The economic threshold was confirmed in a designed trial where it resulted in acceptable levels of fruit damage. The 1-min scouting method and economic threshold was validated in 17 commercial crops in the Gisborne, Poverty Bay region of New Zealand. Scouting in these fields was based on 10 plants in each of four quadrants proportionally representing the topography of each field. In unsprayed areas, egg and larval populations were usually below the economic threshold in early-planted crops but often exceeded thresholds in late-planted crops. In commercial demonstration trials where standard calendar spraying practice was compared with no spraying, calendar-based applications maintained fruit damage below 3.4%, but insecticide was applied unnecessarily to more than half the crops. Larval populations were a significant predictor of damage in these commercial crops. In 12 implementation trials, where spraying recommendations were based on the 1-min scouting threshold of one larva per plant, the worst fruit damage observed was 2.3%. The definition of an economic threshold, scouting methods, and establishment of parasitoids have reduced spray applications and contributed to the implementation of an integrated pest management program for processing tomatoes in New Zealand.