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- Seedling Cotton Injury
Originally published May 5, 2020.
In the past week, I have looked at a few central Louisiana cotton fields that appeared to have severe thrips injury, yet no adult or immature thrips were present. Thrips are often one of the first factors people attribute to seedling cotton injury. However, several factors can contribute to early-season cotton injury. These include cold temperatures, insect feeding, preemergence herbicides, sand blasting, seedling disease and water stress. Fields planted in April often will experience some form of environmental stress that delays seedling growth and vigor. Severe issues often arise when these factors become additive, such as chilling injury coupled with use of preemergence herbicides. Much of this injury will look very similar to thrips and is easily mistaken as such. This type of injury can lead automatic thrips sprays when they are not warranted.
The key to making thrips rescue sprays is the presence of immatures. When immatures begin to appear, this means the seed treatment has broken and reproduction is occurring. Luckily, thrips numbers appear to be low thus far in 2020 and are primarily composed of tobacco thrips; however, this can quickly change and may differ across the state. If a rescue spray is deemed necessary, the decision should be made based on the presence of immature thrips and not old thrips damage or other non-insect related damage.
Below are some considerations when deciding what foliar insecticide to use.
Dimethoate:
Positives: Relatively inexpensive, decent efficacy at high rates, less likely to flare spider mites and aphids than acephate.
Negatives: Less effective on western flower thrips, less effective than acephate or bidrin when applied at lower rates.
Acephate
Positives: Relatively inexpensive, effective towards western flower and tobacco thrips.
Negatives: May flare spider mites and aphids if present.
Bidrin
Positives: Effective, less likely to flare spider mites and aphids than acephate.
Negatives: More expensive, less flexibility with applications early season.
Intrepid Edge
Positives: Effective, unlikely to flare spider mites and aphids. Intrepid Edge is a mix of Radiant and Intrepid. Activity is similar to Radiant.
Negatives: Requires the application of two modes of action but only gets the benefit of one.
If you have any questions or concerns please contact your local county agent or AgCenter specialist.