Cotton Insect Update

Jeff Gore, Research and Extension Entomologist
By Jeff Gore, Research and Extension Entomologist and Angus Catchot, Extension Entomologist August 3, 2013 10:54

Several insect pests have started to show up in cotton over the last couple of weeks.  In most cases in the Delta, applications have shifted from targeting plant bugs to targeting plant bugs plus at least one other pest. In most of those situations, tank mixes with multiple insecticides are needed to control the whole complex.  In this update, we will attempt to cover all of the current pests and highlight some control options.

Tarnished Plant Bug

Tarnished plant bug populations have continued to be high in most areas of the Delta this year.  This is pretty typical for the Delta considering that most of the cotton is now well into flowering.  Populations have also been unusually high in the Hill regions this year and more applications are being made compared to previous years.  Control options are likely to be drastically different in the two regions.

High levels of resistance to most insecticides occur in populations in the Delta.  As a result, high rates of tank mixes are needed to obtain adequate control.  Acephate at 0.75 lb ai/A or higher or Bidrin at 8 fl oz/A mixed with a pyrethroid has continued to provide the best control. Another good option is Transform.  Under high populations like we typically see in the Delta, two applications will probably be needed at the 1.5 oz rate.  Control can be improved by adding a pyrethroid to the 1.5 oz rate or increasing the rate to 2.0 oz/A.  Also, as we move into peak flower, it is a good idea to bring Diamond back into the mix.  At this time of year, it is also a good idea to bring neonicotinoids back, but they will need to be mixed with a pyrethroid to get the best level of control at this time of year.

In the Hills, populations can usually be controlled with a single application of most of the currently labeled insecticides.

Cotton Aphid

Cotton aphid populations have blown up over some areas of the state recently.  In most areas of the state, cotton aphids are resistant to the neonicotinoids.  The best options for cotton aphid control include Carbine and Transform.  Fortunately, populations seem to be starting to crash, presumably from the Neozygetes fungus.  I saw some aphids today (8/2) at Stoneville that appeared to be infected with the fungus.

Spider Mites

Spider mites continue to persist in most areas of the state, especially in areas that have missed rain over the last couple of weeks.  As a reminder, control with abamectin based products is becoming less consistent.  If abamectin is used, the minimum rate should be no less than 8 oz and 10 to 12 oz would be better.  Other options include the older miticides Dicofol or Comite II and the newer miticides Portal or Zeal.

Bollworms

The bollworm flight has been about two to three weeks later than normal this year, but seems to be sweeping across the state now.  There have been a lot of questions about what to use for bollworm control in dual gene cottons.  The pyrethroids have been less consistent over the last few years.  We have been looking at the benefit of using Prevathon on dual gene cotton for about 3 years now.  In general, we have seen yield increases ranging from 60 lbs up to 300 lbs of lint per acre from 1 to 2 applications of Prevathon when bollworms are present.  Similar results can probably be achieved with Besiege.  Both of those insecticides provide long residual control, but are fairly expensive.

The big question we are starting to get is: Should I use Prevathon or Besiege as a preventative treatment in dual gene cotton?

That is a difficult question to answer.  There are a lot of factors that need to be considered when making that decision.  Our research has shown an average yield increase of around 150 lbs of lint per acre.  That research was done using Prevathon at 20 to 27 oz per acre.  Those are fairly expensive rates, but 150 lbs of lint is more than enough to justify spraying.  One important point that needs to be considered is what is going to happen the rest of the season.  There are still several weeks left in the season and more insecticide sprays will most likely be needed, especially in the Delta.

Prevathon or Besiege can definitely provide a benefit in dual gene cottons when bollworm populations are present.  However, it will be important to maintain high levels of plant bug control throughout the rest of the season.  It is not worth spending the money on these insecticides to protect 150 lbs of lint if you start cutting plant bug sprays.  Based on our experience, cutting plant bug sprays before cutout can result in yield losses much higher than 150 lbs.  The bottom line is that we don’t want to spend $25-30 to make 150 lbs of lint and then try to save money later by cutting rates on plant bug sprays and lose 300 lbs.

Finally, it will be important to not give up on this years crop.  Plant bugs are capable of causing the greatest yield losses and should be at the forefront of the overall insect management program.  Other insects should be managed accordingly based on their potential to reduce yields.  Ranking the remaining insects for their potential yield loss from highest to lowest would be bollworms, spider mites, and finally cotton aphids.

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Jeff Gore, Research and Extension Entomologist
By Jeff Gore, Research and Extension Entomologist and Angus Catchot, Extension Entomologist August 3, 2013 10:54
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