An adjustable action threshold using larval parasitism of Helicoverpa armigera (Lepidoptera: Noctuidae) in IPM for processing tomatoes

Published source details Walker G.P., Herman T.J.B., Kale A.J. & Wallace A.R. (2010) An adjustable action threshold using larval parasitism of Helicoverpa armigera (Lepidoptera: Noctuidae) in IPM for processing tomatoes. Biological Control, 52, 30-36.
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This study is summarised as evidence for the following.

	Action	Category
	Incorporate parasitism rates when setting thresholds for insecticide use Action Link
	Use pesticides only when pests or crop damage reach threshold levels Action Link

Incorporate parasitism rates when setting thresholds for insecticide use

A controlled study in 2000-2002 in Hawke’s Bay, New Zealand (Walker et al. 2010) found that tomato Solanum lycopersicum damage from cotton bollworm Helicoverpa armigera larvae did not exceed the commercially acceptable level of 5% on 16 of 17 occasions when treatment decisions were based on parasitism-adjusted pest thresholds. Only 1.2-5.5% of tomatoes were damaged in 11 fields where decisions to not spray crops used thresholds accounting for parasitism (damage exceeded the acceptable 5% level in only one field), and 3.0-3.4% were damaged in two sprayed fields where conventional thresholds (using pest but not parasitism levels) were used. Tomato damage averaged 3.9-7.1% in three unsprayed fields where cotton bollworm numbers exceeded parasitism-adjusted threshold levels. Treatment decisions were made for 22 fields which met or exceeded a conventional threshold of one cotton bollworm larvae/plant, suggesting spraying was necessary. However, in 16 fields and one half-field, crops were only sprayed if bollworm numbers exceeded thresholds adjusted for site-specific parasitism rates (ranging 1-8.3 larvae/plant). Controls included two fields sprayed when only the conventional pest threshold was exceeded, and three fields and one half-field left unsprayed despite exceeding all thresholds. Insecticides included spinosad and Bacillus thuringiensis pesticidal bacteria. Fruit damage was assessed for 40 random plants/field.
Use pesticides only when pests or crop damage reach threshold levels

A trial in 2000-2002 in Hawke’s Bay, New Zealand (Walker et al. 2010) found that tomato Solanum lycopersicum damage did not exceed the commercially acceptable level of 5% at harvest on 16 of 17 occasions when decisions to spray were made using thresholds of cotton bollworm Helicoverpa armigera larvae abundance. On average, 0.8-5.5% of tomatoes were damaged in treated fields compared with 3.9-7.1% in unsprayed fields (where thresholds were also exceeded). The decision to not treat crops while maintaining < 5% damage was correct 10 out of 11 times. Treatment decisions were made for 22 fields which all met or exceeded a conventional threshold of one larvae/plant. However, in 16 fields and one half-field, spraying only took place if larvae numbers exceeded an adjustable threshold accounting for site-specific parasitism rates (see 'Incorporate parasitism rates when setting thresholds for insecticide use'). Thresholds varied from 1-8.3 larvae/plant. Insecticides included spinosad or Bacillus thuringiensis pesticidal bacteria. Fruit damage was assessed for 40 random plants/field. Three fields and one half-field were left unsprayed to assess crop damage without treatment, but the effects of spraying with and without a pest threshold approach were not compared. Effects on natural enemies were not presented.