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24
Jun
2012
Cotton insect update: keep the sweep net in your hand
Author: Gus Lorenz, Extension Entomologist

Plant bug pressure is really ramping up this week.  With a lot of corn beginning to mature and silks turning brown, we are seeing migration of plant bugs out of corn into adjoining cotton fields.  We have a unique situation right now.  With a lot of cotton beginning to bloom, this is the time we usually switch to shake sheets and put away the sweep nets. With this migration of adults from corn (and wild host, early soybeans, etc), it’s a good idea to keep that sweep net going for a little while. We put out a couple of plant bug trials this week outside Marianna.  We are finding about 10 adults per 25 sweeps but only a nymph or 2 with a shake sheet.  The sweep net is so much better for detecting adults than a shake sheet that at least for a little longer you might want to keep that sweep net in the game plan. The shake sheet is still the preferred method for detecting nymphs, but at least in the fields we are checking right now, the sweep net is giving a better reflection of numbers because the adults are moving into the fields now.  As always, monitoring for square retention is critical.  In the trials we are conducting, square retention next to corn is really falling fast due to adult feeding, and several plots had less than 80% square retention. We want to maintain square retention at 80% or greater to maintain yield potential.

In our trials, the standard treatments appear to be reducing plant bug numbers, but it appears that to maintain square retention another application will be needed.  With numbers like 10 adults on 25 sweeps, we are about 4x threshold of 9-12 per 100 sweeps.  With mass migration into the cotton from the corn field next to us, it’s really hard to determine how good an application is at this point without monitoring square retention.  In this situation, multiple applications may be required to knock numbers down to an acceptable level.  This situation is obviously worst right next to the corn, and the further away from corn, the lower the number of plant bugs, so strip treating may be the way to economically treat this situation.  If you don’t have to treat the whole field, save some money and treat only as much of the field is necessary to achieve adequate control.  At our location, numbers of plant bugs really drop off about 35-40 rows into the cotton field.  Some fields have corn on two or three sides, and it may not be possible to strip treat every field, but where possible, it can certainly save the grower some money.

There have been a lot of questions about Transform, which recently received a section 18 for use in cotton.  I strongly urge you to read the 18 before considering use of the product.  One issue is the plant back restriction for all other crops of 360 days; therefore, use of Transform will mean cotton has to be planted back in the field next year.  If the product receives a full label that restriction will be lifted.  While a full label is expected, you never know what will happen.  At a projected cost of $12 per acre the product will, in most cases, be limited to situations where plant bugs are problematic and difficulty in control is experienced.  At the 1.5 oz/ A rate, control is very good on moderate populations but may not achieve the level of control expected for the price tag if plant bug numbers are really high.  We have worked with this product for the last several years, and I have no qualms in saying that this product performs equal to or better than currently labeled insecticides for plant bug control, but just like everything else there are no silver bullets.  I just don’t want to see expectations too high, especially in the situation I described above where massive numbers of plant bug are moving into the field.  Just remember, nothing out there is going to “zero out” plant bugs in the field.  In my experience, we never see that with any product.

Transform has the potential to really help with plant bug control.  It’s a new class of chemistry and can help take the pressure off of some of our other insecticides with resistance issues looming.  In high populations, like other products, tankmixing Transform may improve control, particularly at the 1.5 oz/ A rate.  Also, we have seen benefit with sequential applications of the product to maximize control.  If you have the right situation, you should try the product and see how it performs for you.


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