Tips for Cotton Thrips

Generally cotton planting would be under way, with thrips management decisions soon follow. We know that mid-April to approximately May 10 planted cotton is historically the most at risk for thrips damage, primarily due to typically slower seedling grow-off conditions.  Curtis Fountain, Duplin Co. agent, put it well.  Why would a tropically adapted perennial plant put a lot of energy into growing quick when you plant it in North Carolina?  Keep in mind that these unfavorable growing conditions, when paired with high densities of cotton thrips can wreak havoc on a seedling.

So where are thrips now?  Based on degree-day modeling, current thrips population development is way behind the 5 year historical average.  Depending on the location, thrips may be behind 2-3 weeks from “normal” in 2014.  This means that our early cotton will still be at risk for thrips, even though it will be planted later than normal.  Also keep in mind that optimum cotton insecticidal seed treatment or at-plant insecticide uptake matches optimum cotton seedling growth- moist soils and warm temperatures.  Moist soil does not equal saturated soil.  A saturated stand will not grow well and will be more at risk for thrips.

If you’ve used a seed treatment or the Admire Pro at-plant + seed treatment combination, keep in mind that residual begins to decline as soon as seed is planted. No more than 2 ½ to 3 weeks activity can be expected with an insecticidal seed treatment alone.  With Admire Pro + insecticidal seed treatment, you can expect 4 to 5 weeks of activity.

If you’re using a seed treatment alone, you’ll likely need an additional foliar application.  If you’re using Admire Pro + seed treatment, you may or may not need the additional foliar spray. Be sure to scout thrips to see if treatment is needed.  Concentrate your attention to live yellow immature thrips in terminals. Older damage can be misleading. The threshold is two immature thrips per plant, with 25% of the plants injured by thrips. Treatment is rarely needed once cotton has reached the five-leaf stage, even if the cotton has been badly injured by thrips.  Avoid treating for revenge.

First true leaf cotton. Image D. Mott.

Foliar application timing for thrips is most effective when cotton is between the expanded cotyledon to first true leaf stage (see photo). Also remember that tank mixes to control both weeds and thrips can reduce application costs. However, a tank mix prioritized for weed control applied after the first or early second true leaf stage may expose the seedlings to significant thrips damage. In this case, separate trips over the field should be made.  Finally, seedlings with “herbicide burn” stress are more subject to thrips damage (another stress). That does not mean, however, that herbicide-burned seedlings have thrips.

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Written By

Dr. Dominic ReisigAssistant Professor and Extension Specialist (252) 793-4428 Entomology - NC State University

Posted on Apr 30, 2014

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