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24
Jun
2012
Soybean insect update
Author: Gus Lorenz, Extension Entomologist

Blister beetle

Blister beetles have been tough this year. We’ve had reports in all areas of the state of this pest invading soybeans, particularly in some of the drier areas of the state. It seems like one of the hardest hit areas is the Arkansas River Valley from Conway up through Fort Smith, but we’ve also seen blister beetles in NE and SE Arkansas.

Adult blister beetles have broad heads and narrow necks.  Several species are recognized.  Two of the most common include the margined and striped blister beetles.  The margined blister beetle is black, gray, or a mixture of the two colors. Striped blister beetles are yellowish-orange with brown stripes.  They are usually spotty in fields and cause severe defoliation in small areas of the field.  When you see one you will see thousands as they like to stay together.  Believe it or not, blister beetles are also considered beneficial because the larval stage eats grasshopper eggs. Pyrethroids such as Baythroid, Declare, Karate, and Mustang Max, as well as Sevin, are all effective for spot treatment control. Check the MP-144 for rates.  If you spot infestations in the field you should treat immediately.  Blister beetles can pick up and leave an area quick; they may move a few hundred yards or a mile at any time.  So if you wait a day or more to treat make sure you go back to see that they are still there or you may waste a treatment.

Striped blister beetle attacking soybean.

Striped blister beetle attacking soybean.

Bollworm/ Corn earworm

Trap counts were holding steady from last week when they jumped over 100 moths per trap in Lonoke. However trap counts this week bottomed out and there is little activity out there. I think the worms will be coming, but for right now let’s enjoy the lull in activity. Remember, check fields that aren’t lapped first as these will be the ones that are desirable to bollworms and other caterpillar pests. The threshold is 9 bollworms per 25 sweeps average in the field.

I’m getting a ton of calls about what insecticide to “throw in” the tank with my R3 fungicide. You have to know that really “punches my button”.  If you have treatment level worms, by all means let’s get them out!  Otherwise, why do you want to spray?  Even a $3 pyrethroid on 500 acres is $1500—I don’t need to do the math for you, you can do that, but I assure you, that pyrethroids will kill the beneficials and just open the door for the bad guys you really don’t want to deal with.  I can’t tell you how many times last year folks would call and say “I can’t believe I already have worms again, I just put out a pyrethroid last week with my fungicide.”—not realizing they created the problem to begin with.  Almost every field last year that got treated with a pyrethroid for threecornered alfalfa hopper, yellow-striped armyworm, etc., were the same fields that had blowout numbers of bollworms a few weeks later.  I know there are a lot of people smarter than me out there, but it certainly isn’t the guy that came over here this year and told growers that  “IPM doesn’t work in soybeans.”  He also said “you should spray a pyrethroid every time you go across the field, they are just too cheap not to” and finally, that Gus Lorenz “didn’t know what he was talking about.”  Well he’s flat wrong on the first two, but at least I know the value of Soybean IPM to our growers and that spraying a pyrethroid every time you “go across the field” is about the worst thing you can do for several reasons: 1) it costs the grower with no return on investment, 2) it flares problem insects like bollworm and soybean looper, and, 3) it promotes insecticide resistance with one of the most effective classes of insecticides we have had for soybeans.  This mentality is what got us to the situation we are in with pyrethroid failures the last 2 years.  With soybean loopers, cotton bollworms and tobacco budworms, and bean leaf beetlesnow showing tolerance/ resistance, it makes you wonder what the value of making a pyrethroid application every chance you get is going to do for you.

I guess that guy didn’t think his words would get back to me—they did.  I feel better getting that off my chest.  Bottom line, if you don’t have a problem, don’t create one.

Finally Angus Catchot wrote a great little piece in their (Mississippi State) blog about soybean insects, things to avoid, and good advice on their blog. I suggest you read it:  Soybeans: Should I Add an Insecticide With the Fungicide?

Stink bugs

Stink bugs are beginning to move into some of the early planted fields that are beginning to pod up. In most cases, we have only seen about half threshold (threshold is 9 stink bugs per 25 sweeps). We are seeing egg masses show up in the field so start looking for stink bugs in early planted fields.


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