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14
Jun
2012
The current insect situation in cotton
Author: Gus Lorenz, Extension Entomologist

Plant bugs:

While plant bug numbers are increasing, they still aren’t quite as bad as many of us thought they would be at this point in the season. Plenty of applications are going out in many areas of the cotton growing region, but numbers aren’t crazy high at this point. That may change as we shift gears into blooming cotton. Traditionally that is the time when plant bug numbers really start climbing quickly.

I have begun to get reports of applications going out, and five days later there are just as many plant bugs as there were, or maybe even more, than before the application.  In most cases,this is just migration out of corn, wild hosts, early planted soybeans, etc. In this case, obviously it is not the lack of control of the insecticide but simply overwhelming numbers moving into the field so plant bug numbers may not be the best gauge of the effectiveness of the insecticide. Rather, you should be looking at square retention. Square retention is the best indicator of whether or not your insecticide application is working and the overall health of the cotton. You hear most of the Midsouth entomologists harping about this all the time but it’s true. As long as your square set is above 80%, you are maintaining maximum yield potential. Several studies have shown that 80-90% square retention is actually better than 95-100% square retention because of the ability of the plant to over compensate and actually results in increased yield. There is no reason to try and hold every square out there; it just doesn’t pay. “Zero Tolerance” for plant bugs will only result in costing the grower more than it should to control plant bugs and won’t increase yield….not where we want to be.

I’ve received several calls on Diamond Insecticide for plant bugs and I want to revisit that subject for just a second. First, Diamond is an insect growth regulator (IGR), and like most IGR’s, it has a couple of characteristics unique to this class of insecticides: 1) it is more effective on nymphs than adults (for reducing numbers) because it causes a fatal molt. Adults are through molting, therefore there is no direct effect on adults. That is why we always recommend using it in conjunction with a “knockdown” material such as Centric, Admire Pro, Vydate, Bidrin, etc., with choice depending on whether it’s before or after bloom; 2) it has very good residual control (stays active on the plant) for extended periods of time compared to other classes of chemistry. This is what makes the product work well for us in cotton.

Our data has shown that in heavy infestations, the best timing for Diamond is around the third week of squaring. That allows the material to be out there on the plant right before we start seeing plant bug nymphs show up. So, what if you don’t have plant bugs? Obviously, you shouldn’t put out Diamond. Diamond, to my knowledge, isn’t a yield enhancer, it’s a yield protector. Just putting it out there because it’s the third week of squaring even though you don’t have plant bugs is just spending money. If plant bugs start building later, put the Diamond out then. Just remember, Diamond is for those situations where plant bugs are a problem, it doesn’t fit every acre of cotton in Arkansas. It will prevent yield loss; it won’t make yield. 

Spider mites:

With recent rainfall in many areas,  spider mites are not as big an issue for many growers and populations will take time to rebuild. Abamectin (Agri-Mek, Abba, Zoro, etc) appears to be doing a good job controlling spider mites. With cheaper prices than the past, this product is going out at 6-8oz/ acre in most cases and working well.


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