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A concern of many cotton farmers now is plant bugs especially if their cotton is near a corn field. North Alabama consultants are finding that tarnished plant bugs are commonly more abundant in cotton fields located next to corn fields. Plant bug numbers at times are much greater in the cotton rows bordering corn than they are in rows near the middle of the cotton field. Research in Mississippi indicates that even though plant bugs do feed and reproduce on corn silks and tassels, the majority of the plant bugs that are found in cotton now next to corn are more likely to be coming from other sources. The plant bugs are most likely flying across cotton fields and when they hit the taller corn plants they turn back and land in the cotton plants near the corn. Plant bugs do reproduce in corn on silks and tassels but most have left corn by the time silks are brown.
We would dare to venture that a significant portion of our cotton crop in north Alabama isn't scouted on a regular basis. Plant bugs can have a devastating impact on cotton so growers need to stay on their toes. A plant bug application should be made from the third week of squaring through bloom (where most of our crop in north Alabama is now) when square retention is dropping and three plant bugs are found per six feet of row with a drop cloth or 15 plant bugs are collected per 100 sweeps with a net. Square retention should not be allowed to drop below 80%. Like stink bugs, plant bugs can also feed on a very small boll after the bloom falls off. Many growers are making growth regulator applications and it would be prudent to put a plant bug treatment, if needed, with this application.
Good options for plant bug control include Centric at two ounces per acre; Transform WG at 1.5 ounces per acre; Orthene at .55 pounds per acre (several growers have said that Orthene is in short supply in NE Alabama); and Bidrin at 3.2-5.3 ounces per acre. Bidrin can only be used after first bloom and it cannot be used from pinhead square to first bloom.
Rotate your mode of action to help avoid insecticidal resistance. Bidrin and Orthene are the same mode of action (1B) so if either of these are used rotate to another mode of action (Centric-4A or Transform-4C) if another plant bug application is needed.
Most growers are also concerned about stink bugs as the cotton begins to set bolls. Our first option for plant bugs at early bloom would be Centric, Orthene or Transform. Growers should save the Bidrin for a later application when stink bug numbers build and they may be more of a threat to cotton. Bidrin is very good on both the brown and green stink bug. The rate of Orthene needs be increased to .75 pounds per acre for good control of stink bugs. Centric will give fair-to-good control of stink bugs. Transform will not control stink bugs.
The concern to preserve beneficial insects also plays a role in which insecticide to use. Bidrin, Centric and Orthene are very hard on beneficial insects. Transform is easy on beneficial insects and if used should help maintain their populations.Transform and Centric are both labeled for aphid control. Aphids are notorious for developing resistance to insecticides and it is hoped that both these products will continue to work in 2017.
Growers may remember in 2014 when cotton was rank and they had trouble killing plant bugs in the lush growth. We have had plenty of rain so far and there is a concern that cotton could be rank. Diamond, an insect growth regulator, at six ounces per acre may be a good investment with our first plant bug application at or near the early bloom stage . It is only active on immature plant bugs and will not control the adults but will help extend plant bug control.
Eddie McGriff, Regional Extension Agent
Tim Reed, Extension Entomologist
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