Cotton Aphids Still Hanging On

Typically cotton aphids show up in MS around the end of June and begin to peak in early July.  However, the last 2 years the bulk of our aphid pressure has been occurring around the end of July.  The fungus, Neozygites fresenii, use to be fairly predictable occurring somewhere around the 4^th – 10^th of July in MS.  In recent years it has been much less predictable and in some cases aphids never crash at all.  In order for the fungus to cause a widespread epizootic, aphid numbers usually have to build to high enough levels for the outbreak to occur.  I don’t know why exactly it has become so erratic, but maybe it’s because of the widespread use of neonics for tarnished plant bug control, not allowing the numbers to build high enough. Not sure, but for whatever reason, we are not seeing aphids crash nearly as timely as in past years.  Also, this year I have had several reports of aphids crashing then increasing back to treatable levels within 10 days.  Currently, there have been some reports for the last 14 days of aphid numbers crashing but they are still high in many areas, particularly in the north delta.

Over the last several years Dr. Jeff Gore has been testing aphids for susceptibility to the neonic insecticides.  He has consistently shown increased tolerance to Centric and Imidacloprid, particularly if the field had previously been treated with a one of these products.  This has created a dilemma for us when we are targeting both plant bugs and aphids.  We currently do not have a product in cotton that will give us good control of both species without a tank mix.  Currently, for the most consistent aphid control we have to use Intruder or Carbine but these are the weakest on tarnished plant bugs so if both are present something needs to be added for the plant bugs. While Centric and Imidacloprid perform better on plant bugs they have become very inconsistent on aphids in MS.

We have quite a bit of data that indicate the addition of an MSO at .5% as the surfactant will increase control with these products when targeting aphids.  I would consider running the Intruder at 1 oz and the Carbine at 2 – 2.2 oz for aphids.  Remember, aphids are not one of those pests that you are going to lose the farm if you don’t act quickly.  On irrigated cotton that is not stressed, I would not be scared to ride them a while in hopes of the fungus showing up.  You may not want to wait as long on dry land cotton that is stressed, particularly if large amounts of honeydew is starting to accumulate.

Below is a test we conducted 2 weeks ago.  Ratings were taken at 3 and 7 days after treatment.  Transform is a new plant bug product from Dow AgroSciences that also has excellent aphid activity.

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