West Texas Cotton: Should I Be on the Lookout for Thrips?

Thrips damaged cotton.

I have noticed some thrips damage on the early planted cotton especially in the areas north of Lubbock. Fields that have already reached 4 true-leaf stage are pretty much safe from further thrips damage.

We still, however, have a lot of late-planted cotton in South Plains that ranges from emergence to 1st or 2nd true-leaf stages which are very prone to thrips injury.

Late planted cotton usually escapes peak thrips flight but the fields at the most vulnerable stages especially those in the vicinity of maturing wheat or pastures will have to be watched closely for thrips.

In general, with the current hot and mostly sunny days, I would not be too aggressive when it comes to spraying as cotton plants can outgrow thrips under good growing conditions.

Having said that, I wouldn’t wait too long either if the damage is being done. Spraying for thrips after the 3rd true-leaf stage contributes little towards the yield—so the timing is critical!

What are thrips?

Thrips are early-season pests of seedling cotton. They are numerous in cotton grown near maturing small grains (wheat) or seedling corn. Thrips attack leaves, leaf buds, and very small squares (flower buds), causing a silvering of the lower leaf surface, deformed or blackened leaves, and terminal and square loss.

Feeding most often occurs in the new terminal growth and on the underside of the leaves. Their feeding ruptures cells, causing stunted plants and crinkled leaves that curl upward. Severe infestations can destroy terminal buds, causing excessive branching of the plants and delayed plant growth.

No damage to severe thrips damage. Click Image to Enlarge

How do I scout for thrips?

Begin inspections once the cotton reaches approximately 50 percent stand emergence. Thrips can migrate in great numbers from adjacent weeds or crops, especially small grains (wheat), and cause significant damage within a few days. Randomly select 20-25 plants from different parts of the field and closely examine them, looking for adult and immature thrips.

Look carefully through the terminal growth, picking it apart with a pencil lead or other pointed object, uncurling all the leaves—thrips often hide in tight locations, especially during rainy, windy conditions.

Thrips on plant terminal

What are the thresholds and control options for thrips?

The threshold for thrips is 1 thrips per true leaf (i.e. at 2 true leaves, it would be 2 thrips per plant; at 3 true leaves, the threshold would be 3 thrips per plant and so on). Research shows that applying foliar sprays after significant thrips damage has occurred results in little or no benefit.

Base your decision to apply insecticide on the number of thrips present and the plant development stage. Foliar insecticides for thrips provide maximum benefit when applied at or before the second true leaf emerges.

Sprays at the four and five-leaf stage after the damage is already done are typically for revenge, rather than yield.

Seed treatments with neonicotinoids (e.g. imidacloprid and thiamethoxam) are still proving to be effective controlling thrips in the Texas High Plains region. However, under heavy thrips pressure, foliar treatment is often needed on the top of seed treatment.

Presence of immatures and injury symptoms on plant are good indicators of whether the seed treatments are working or not. As far as foliar treatments are concerned, acephate, dicrotophos (e.g. Bidrin 8EC), and spinetoram (e.g. Radiant SC) all provide an excellent thrips control. You can tank mix your insecticide with a post emergence herbicide application.

The decision you will likely make is whether to be timely for the weeds or the thrips. Remember, no insecticides are approved for tank mixing with applications of any dicamba products in cotton.

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