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08
Aug
2012
Update on the insect situation in Arkansas
Author: Gus Lorenz, Extension Entomologist

Cotton

Plant Bugs

They just won’t let up will they? With cotton winding down fast and many fields having reached NAWF=5 (physiological maturity), many of us are counting heat units (DD 60’s). Research tells us when we reach 250 HU’s we can terminate insecticide applications and suffer no yield or quality loss from plant bugs.   Some cotton is already there but a whole lot more isn’t there quite yet.   The deal is, you want to go into 250 HU’s past NAWF=5 clean.  The problem is, very few acres are “clean” at 250.  In fact, many folks simply can’t get plant bugs down below one per row foot.  I’ve received several calls the last few days where people have sprayed in the last week only to go back at 5-7 days and actually find more plant bugs than when they treated.  Very frustrating to say the least, not only for them but for any so-called expert, that can’t provide a solution (that would be me).  The silver lining to this cloud is the fact that square retention/ boll damage appears to be minimal.  This reminds me, that for many of these fields, you need to be looking at quarter-sized bolls as much or more than square retention to assess success of insecticide applications at this point.  Hopefully everyone is using tank mix applications as we have suggested and shortened the time interval between applications to aid in reducing plant bug numbers.  Just to give you an idea of how intense plant bug pressure is right now, we scouted our plant bug control plots today at Marianna.  I had one shake sheet sample in an untreated check that had 106 plant bug nymphs on 5 row feet.  That’s over 21 plant bugs per row foot.  With a threshold of 3 per 5 row feet, you can see the difficulty in reducing numbers to a sub-threshold level.  At 90% control, which nobody is reaching, that would leave about 11 plant bugs per 5 row feet or about 3.5X threshold.

We are having the best luck with Acephate + Bifenthrin, Bidrin + Bifenthrin, Endigo and Transform + Bifenthrin.  As you can imagine not many treatments are reducing numbers below threshold, but they are protecting the fruit.  Obviously nothing out there is zeroing out plant bug numbers in this situation.  I don’t know about you, but I’m getting real tired of plant bugs at this point.

Spider Mites

We are getting quite a few calls on when we can terminate insecticide applications for spider mites. Unfortunately, we have to go out a little farther with spider mites.  Premature defoliation can halt boll development, and similar to defoliators, we need to insure adequate leaf area to fill out bolls.

Soybean

Corn Earworm (or Bollworm) appears to be getting worse in some areas.  While our trap counts in central Arkansas were down last week, they peaked in Northeast Arkansas in several areas and larval numbers have jumped.  Rick Thompson, consultant and former county agent in Poinsett Co., reported fields with over 100 bollworms on 25 sweeps in fields in the Poinsett/ Craighead County area this weekend.  Bollworms continue to hit fields the hardest that are late-planted, not lapped, and beginning to bloom and set pods.  However, word of warning, we are also seeing fields that are lapped have treatment level bollworm.  So, scout all fields.  We found several fields that were R4 (3/4” pod) and R5 (full size pod) that had treatment level (9 worms/ 25 sweeps) bollworms.  We have received several calls on less than adequate control on fields with pyrethroid applications. Despite our warnings, several folks have tried pyrethroid applications and for the most part, they have gone as expected—not very well.  We have received a few calls on failures with other treatments, but they usually go back to application issues.  Belt and Steward and a pyrethroid + acephate all appear to be providing excellent control for bollworms.

Loopers are also popping up in the southern part of the state.  Evidently we had a big flight down there last week, and as a result, several fields now have fairly high levels of loopers that range in size from neonate to ¼- ½ inch long and are running upwards of 4-5 per row foot.  I predict by the end of this week and first of next week several fields may require an insecticide application.  While at Marianna today, we saw several looper moths flying around which may indicate the population is pushing north.  I encourage everyone to get out there and scout your fields close in the coming weeks.  It appears the fields being hit are R5 and R6 fields fully lapped.  Remember loopers start out at the bottom of the plant and work their way up so when you see loopers blowing out the top, you have already missed the treatment window.  That means you actually have to get out of the truck and scout.  Sorry.  Products of choice include Belt, Intrepid and Steward.

Rice

I know, you probably thought we had got past the whole stink bug deal without a hitch; however, stink bugs are definitely beginning to show up in late-planted rice.  Numbers are not bad, usually right at threshold (10 stink bugs/ 10 sweeps) or just above or below the threshold.  We encourage you to scout those late fields closely.

I can see the light at the end of the tunnel…hang in there, maintain your vigilance, let’s protect this crop for a little longer, and maybe we can enjoy a very cold winter….I’m ready, how about you?


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