Journal of Insect Science (2008) 8 (49), 9-10

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P.C. Ellsworth and S.E. Naranjo (2008)
Action thresholds and selective insecticides for management of Lygus in Arizona cotton
Journal of Insect Science 8 (49), 9-10
in P.B. Goodell and P.C. Ellsworth, organizers: Second International Lygus Symposium, Pacific Grove, California, April 15-19 2007
Abstract: In most years over the last decade, on a relative basis, cottongrowers have sprayed and spent more to control Lygus spp. (mainly L. hesperus), and have lost more in yield to this pest than any other insect. As major advances were made in the control of pink bollworm with Bt transgenic cottons and whiteflies [Bemisia tabaci (Genn), biotype B] with selective insect growth regulators, Lygus bugs have become a more important management focus for growers. Over the last decade, studies in Arizona cotton have focused on the development and refinement of action thresholds, termination rules for chemical control, and the identification and development of selective chemistries that will permit further gains in conservation biological control in our system. We identified 15 total Lygus per 100 sweeps as a density associated with economic loss; however, correlations of "total Lygus" with yield were weak. Nymphs, however, especially large nymphs (instars 3-5), were best associated with yield loss over a wide range of conditions. Regression analyses showed maximal yield at 15 total Lygus with at least 1.7 nymphs per 100 sweeps. However, revenues were maximized over a wide range of economic conditions at 15 total Lygus with at least 5.2 nymphs per 100 sweeps. Extension guidelines were taught to growers and implemented in AZ and Mexico using action thresholds of 15 total Lygus with at least 4 nymphs per 100 sweeps ('15:4'). As the plant senesces and fewer flowering/fruiting sites are produced, the need for and return on control investment diminishes. Termination rules for discontinuing Lygus chemical controls over twelve different production scenarios (2 planting dates x 2 irrigation termination timings x 3 different maturity groups) revealed an extremely dynamic relationship between yield/revenue and bug density. Generally, shorter season varieties benefit less from extended protection from Lygus. Longer season varieties appear to be especially vulnerable to Lygus damage and therefore more responsive to Lygus controls. Cotton producers have historically depended on very old and very broad-spectrum chemistry for Lygus control, tending to place the grower at greater risk of pest resurgence and secondary pest outbreaks. Exploratory studies with new chemistries over the last 5 years have brought forth two promising control agents, metaflumizone and flonicamid, with new opportunities for selectively controlling Lygus. Large plot studies have confirmed that usage of these new compounds leaves a complex of natural enemies intact relative to untreated controls, whereas broad-spectrum standards like acephate dramatically reduce the natural enemy community. The integration of this new understanding in density:damage relationships (e.g., improved action thresholds) and new selective chemistry for control of Lygus completes a system for Arizona cotton growers that allows them to manage pests without potentially costly disruptions with broad-spectrum materials while fostering a richer and more functional natural enemy community.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Database assignments for author(s): Peter C. Ellsworth, Steven E. Naranjo

Research topic(s) for pests/diseases/weeds:
control - general

Pest and/or beneficial records:

Beneficial Pest/Disease/Weed Crop/Product Country Quarant.

Lygus hesperus Cotton (Gossypium) U.S.A. (SW)