Early season insect issues in cotton typically begin with thrips and this year is no exception. Thrips are be-ginning to appear in young cotton (1st to 4th true leaf) with tobacco thrips composing the primary species pre-sent with western and eastern flower thrips present at lower numbers. Adding to this issue, Syngenta has confirmed resistance to thiamethoxam, the active ingredient in Cruiser, Avicta Complete, Avicta Duo and Ac-celeron N seed treatments in four populations of tobacco thrips collected in the Mid-South. Therefore, cotton treated with thiamethoxam may not give adequate control of tobacco thrips populations in Louisiana, howev-er; western flower thrips still appear to be susceptible.
Based on limited data, resistance appears to be con-fined to thiamethoxam and has not been detected with imidacloprid.
Foliar treatments should be made when immature thrips are present and/or when large numbers of adults are present and damage is occurring. The presence of immature thrips often signifies that the insecticide seed treatment has lost is efficacy. Avoid spraying solely based on plant injury since the damage has al-ready occurred. Below are some considerations when deciding what foliar insecticide to use.
Dimethoate:
Positives: Relatively inexpensive, good efficacy at high rates, less likely to flare spider mites and aphids than acephate
Negatives: Ineffective towards western flower thrips, less effective than acephate or bidrin when applied at lower rates
Acephate
Positives: Relatively inexpensive, effective towards western flower thrips
Negatives: May flare spider mites and aphids if present, may be weaker against tobacco thrips
Bidrin
Positives: Effective, less likely to flare spider mites and aphids than acephate
Negatives: Less flexibility with applications early season
Radiant
Positives: Effective, least likely to flare spider mites and aphids
Negatives: More expensive, requires adjuvant
Insecticide choice depends on a number of factors such as cost, impact on secondary pests and spectrum of thrips species present. If a foliar thrips treatment is justified, do not wait for a glyphosate application and only spray when necessary to avoid flaring spider mites and aphids.
