Cotton Aphid Update

Jeff Gore, Research and Extension Entomologist
By Jeff Gore, Research and Extension Entomologist and Angus Catchot, Extension Entomologist July 20, 2012 20:40

Aphids have really been blowing up recently in cotton across Mississippi, so I wanted to give a quick update on our bioassay results from this year.  To date, I have not tested a single colony that was susceptible to neonicotinoids.  Cotton aphids have a long history of rapidly developing resistance to all classes of insecticides.  It is surprising that the neonicotinoids have remained effective for as long as they have.  As most everyone knows, cotton aphids have been resistant to the OP’s and pyrethroids for a long time. 

Bidrin and Cotton Aphids?

Every year we get multiple questions about Bidrin and cotton aphids.  In some areas of Mississippi, Bidrin may show some suppression of cotton aphids, but I wouldn’t count on it.  The main benefit of Bidrin is that it is the least likely insecticide of the OP’s and pyrethroids to flare aphids after an application. This can easily be confused with suppression, especially when you compare a field where acephate has been sprayed and populations increase rapidly to one where Bidrin has been sprayed and the population increase is slower.

Status of Neonicotinoids

As for the neonicotinoids, they are not all created equal.  Intruder will still give some level of control when used at the highest labeled rate (1.1 oz/A) and 0.5% MSO is added.  However, even Intruder seems to be less consistent than it was a few years ago.  The other neonicotinoids are even less consistent and in some fields may actually flare aphids. 

Control Options

For effective control, there are only two good options at this time.  Carbine has continued to perform well, especially in fields where failures have been experienced with the neonicotinoids.  Carbine should be used at a rate of at least 2.0 oz/A and more is always better.  Rates below 2.0 ounces can be very inconsistent.

The other option is not really an option (at least not everywhere in Mississippi).  If tarnished plant bugs are in the field and you are in one of the counties listed on the Section 18, then Transform will also clean up cotton aphids that are in the field.

Fungus Update

Fortunately, it appears that the aphid fungus, Neozygites fresenii, epizootic is starting in parts of Mississippi.  We are getting reports of the fungus from the south Delta and hopefully it will spread fairly rapidly across the rest of the state. Unfortunately, it is very difficult to predict how widespread the fungus is without a monitoring program.  A lot of things can cause aphids to crash.  The difference between these other factors and the fungus is that the aphids can rebound fairly quick behind if they crash due to something other than the fungus.

We should know if a true epizootic has started in Mississippi within the next week to 10 days. In the meantime, we will try to keep everyone updated on what is going on with the fungus.

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Jeff Gore, Research and Extension Entomologist
By Jeff Gore, Research and Extension Entomologist and Angus Catchot, Extension Entomologist July 20, 2012 20:40
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