Posted 28 May 2015. PMN Crop News.
Should You Spray for Cotton Thrips?
Source: North Carolina State University Press Release. harvest.cals.ncsu.edu
Raleigh, North Carolina (May 10, 2015)--What is the growth stage of the cotton? I cannot stress the importance of this point. Cotton is most susceptible by far before the two-leaf stage. Cotton will take a yield hit up to the five leaf stage, but sprays at the four and five-leaf stage are typically for revenge, rather than yield. You can tank mix your insecticide with a post herbicide application. The decision you will likely make is whether to be timely for the weeds or the thrips.
What are your thrips numbers?
Our threshold is two nymphs per seedling at or before the first leaf stage. Note the importance of spraying your cotton early. Finally, the majority of fields in our state without imidacloprid in-furrow will greatly exceed the economic threshold, justifying sprays.
When did you plant?
On average, cotton planted after the 17 of May is safe from thrips. The earlier you plant, the more likely you are to suffer from thrips. This varies from year to year, of course. Last year, cotton planted mid-May was hammered by thrips. This is because the two most critical factors for thrips injury in cotton are the “thrips flight” and how fast the cotton grows (cooler conditions mean slower grow off for the cotton). Last year’s thrips flight just happened to be timed so that our cotton planted during mid-May was at severe risk. Both weather and the thrips flight are unpredictable at this time, although a model is in development to predict risk to cotton.
What is your insecticidal seed treatment?
Acceleron I, FI, N, NPV, etc., as well as Aeris and Gaucho are imidacloprid alone or in combination with clothianidin. These seed treatments are far and away what have been offered on our seed this year. A little seed will be treated with Avicta or Cruiser, which is thiamethoxam. Tobacco thrips are now resistant to neonicotinoid insecticides in our state, although the resistance levels in 2014 varied among geography. In general, although there is imidacloprid resistance out there, field performance of this chemical seems to be superior to thiamethoxam. Bottom line, if you only have thiamethoxam seed treatment, spray insecticide at the one leaf stage. If you have imidacloprid-treated seed, keep an eye out for how it is performing.
Did you use imidacloprid in-furrow?
Our recommendation for the past two years has been to use the highest labeled rate of imidacloprid (Admire Pro) in-furrow overtop of insecticide-treated seed. The rationale for this is that, when the imidacloprid was applied correctly in replicated tests, a foliar spray for thrips was not necessary. Even though thrips were neonicotinoid resistant in 2014, the cotton seemed to take up enough insecticide with this shot in the furrow to overcome the thrips. We do not know how this will hold up in 2015. Also, if the application method is not correct (not applied directly in-furrow with good insecticide to seed contact), you will likely need to spray.