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11
Jul
2013
Plant bug and spider mite activity picking up in cotton
Author: Gus Lorenz, Extension Entomologist

Plant Bugs

Things are beginning to heat up out there and insect activity is on the uptick. With much of the cotton crop beginning to bloom, plant bugs are really moving into cotton right now. We’ve been seeing plant bugs in wild hosts for some time now and predicted that plant bugs might be pretty tough this year—I think I finally got one right.  It appears that numbers are going from just a few, to as many as 60 plant bugs per 100 sweeps. Remember, our threshold with the sweep net is 9-12/ 100 sweeps.  I have had several reports from all over the cotton region of counts from 15-20 to 40-60 per 100 sweeps, and it’s always the same scenario: the cotton is around the 10-12th and there is a corn field nearby.  I think in some cases, you can substitute the corn field for fields with large areas of blooming weeds nearby too. Anyway, these fields went from just a few plant bugs a week ago to up to 5X threshold this week.  In most cases, the corn is beginning to reach brown silk and plant bugs are coming out of the corn.  Another consideration is the hot dry weather for much of the growing region, and in most of the state it’s getting dry and the weeds on levees and ditch banks are drying out, so we are getting an influx of plant bugs from this source too.  With cotton blooming in most fields now and plant bug numbers increasing, it may be time to consider options.  If plant bug numbers are rapidly increasing, this is the time when tank mixes can really help get the plant bugs under control.  Options of a knockdown material like Centric, Bidrin or Orthene with Diamond might be a choice.  Also, with cotton blooming, it may be time to think about Transform too.  Just remember with both Diamond and Transform, we’ve seen better control using these products in consecutive applications, that is two shots of Diamond at 6 oz with a knockdown material or Transform at 1.5 oz 7-12 days apart depending on plant bug numbers.  I’ve already received calls where a single product was applied and plant bugs were back above treatment level in 5 days.  In those really bad plant bug situations, remember that 2 applications 5-7 days apart are often necessary to get numbers under control.  If plant bugs aren’t that bad, stay with your tried and true approach.  In some parts of the state, plant bugs are there but aren’t “blowing up.”  If that’s the case, don’t get excited, just treat as needed and use the products that have always worked for you.

Remember too, square retention is equally important to plant bug numbers on making management decisions.  Keeping square retention around 80-85% is the goal, not 95 or 100%. With cotton beginning to bloom, we will transition into shake sheet counts.  Three per 5 row feet is the threshold.  We definitely want to get plant bugs to an acceptable level before the canopy closes up, because we know how difficult plant bugs can be to control once that happens.  It just becomes difficult to get good coverage down in the plant.

Spider Mites

With the hot, dry weather we are also seeing spider mites beginning to become an issue all across the cotton growing region.  If you haven’t heard, there have been some issues in Mississippi, Louisiana, and Missouri of not getting adequate control of spider mites with abamectin (Agri-Mek, Abba, etc.). This has been the product of choice for most of us because once it went off patent a few years ago, there were many companies that began to produce it, and competition drove the prices down.  As a result, it became much cheaper than other miticides, and it has been used almost exclusively now for the last several years around the Midsouth.  If you have used this product in the last couple of weeks, I recommend you watch closely to see if you are getting adequate control.  Abamectin works slowly.  You cannot go behind an application and see decent control in 3-5 days.  Our experience with the product has been that you begin to see some control at about 7-8 days, decent control in 10-11 days and by 12-14 days the control has been very good.  So, don’t try to evaluate control too early.  If by 7-8 days population has not gone down or by 10-12 days control is not adequate, you may be experiencing a problem with control.  Certainly if numbers are increasing from the time you treated, there is definitely a problem.  In that situation, what you should not do is make another application of the product.  Don’t try to increase the rate you previously used and make another application.  Go to another miticide such as Oberon, Portal, or Zeal.  These are all different chemistries and should provide good control.  The only problem is they are more expensive.  Several folks have abamectin out right now and at this point, no failures in Arkansas have been brought to our attention, but we need to be vigilant and watch for developing problems.  We will let you know as soon as possible if we see any problems developing.

Spider Mites and Plant Bugs

Many folks have both spider mites and plant bugs which require a tank mix of insecticides for control of both pests. We have tank mixed most of the miticides and plant bug materials in trials the past couple of years and have not experienced any issues with combining the products.

Information provided by Drs. Gus Lorenz and Glenn Studebaker 

 


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