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09
Aug
2019
Row Crop Insect Update, August 8.
Author: Ben Thrash, Extension Entomologist

Ben Thrash, Gus Lorenz, Nick Bateman, Glenn Studebaker

August 8, 2019

Cotton

In south Arkansas this past week there has been a huge flight of bollworm moths and these numbers are not being reflected in our moth traps.  We think this is due to a large amount of pheromone in the air from the moths which is overwhelming the pheromone in the traps.  I have been told that back in the day, when boll weevil numbers were extremely high, a similar phenomenon would occur. These moths are making their way North and several people are beginning to find them in a few spots around Marianna and creeping up past I-40.

Several people have treated with a diamide on two gene cotton and 10 days later got a 100% egg lay.  We know that the diamides provide longer residual control than that, however this is a situation where 90% control wouldn’t be good enough.  If put in this position we recommend using bifenthrin + acephate in order to knock down some moths and kill some small larvae when they hatch. It is too soon and too expensive to go back to back with another diamide application. So far our three gene cotton has been providing good control.

Non-Bt, WideStrike, TwinLink, and BG2 cotton varieties:

Before bloom: Treat when population reaches or exceeds 8 larvae/100 plants or 6% fruit injury of any kind.

After bloom: Treat when you find 20-25 eggs/100 plants or 6% fruit injury of any kind.  Regardless of size of larvae, treatment may be warranted if damaged-boll counts exceed 2 percent and significant numbers of larvae are present and continuing to cause damage.

*If treating on eggs with a diamide insecticide, do not make additional diamide applications on eggs sooner than 12-14 days apart.

WideStrike 3, TwinLink Plus, and BG3 cotton varieties:

Before bloom: Treat when population reaches or exceeds 8 larvae/100 plants or 6% fruit injury of any kind.

After Bloom:  Treat when larvae 1/8-inch long or longer exceed 4 larvae/100 plants or 6% fruit injury of any kind.  Regardless of size of larvae, treatment may be warranted if damaged-boll counts exceed 2 percent and significant numbers of larvae are present and continuing to cause damage.

We have seen a resurgence in plant bugs this past week. Most people are using acephate + bifenthrin at this time or Bidrin + bifenthrin.  Both are providing excellent control in our plots this year.  If aphids or spider mites have been a problem where you are, Bidrin may be a better choice between the two, it tends not flair these pests.  Aphids are spotty throughout the state and unless they are really bad we don’t recommend an application solely for aphids.  Generally its best to wait and spray Transform at the next plant bug application.  Spider mites have flared up in a few areas in NE Arkansas requiring treatment. Remember if abamectin was used to control mites and they resurge on you, don’t come back with abamectin a second time.  Switch to another chemistry such as Portal, Zeal or Oberon.

Stinkbugs are also showing up in places.  Our threshold for stinkbugs is 1 per 6 row feet or 20% boll damage. Checking for damaged bolls is easy, just break open 10 nickle to dime sized bolls and look for discolored lint or warts on the inside of the boll wall. Remember, plant bugs can also cause damage on these bolls and later in the season when bolls are in the top of the plant, we need to move from checking square retention to checking for damaged bolls.

Lets talk for a second about insecticide termination timings. The cutout date for cotton in Arkansas is August 8 in North AR and August 21 in South AR.  This means fruit present on this date has a 50% chance of making a mature boll. We can terminate insecticide timings for plant bugs at NAWF 5 + 250 heat units, bollworms at NAWF 5 + 350 heat units, and stink bugs at NAWF 5 + 450 heat units.  There is no termination date for spider mites and you must treat for them until you are ready to defoliate the cotton

Soybean

Similarly to cotton, lots of bollworms are being found in open canopy blooming beans. The virus (Heligen) has been performing well for lots of people.  With that being said we looked at a couple of fields yesterday where the virus was getting overwhelmed by the sheer number of worms in the field. The virus had been sprayed 10 days previously and there were no large worms to be found, that tells us that it worked. We could find many small, virus dead, dying, and lethargic larvae in the field, however there were still lots of small healthy worms and lots of moths to boot. Another classic situation of 90% control not being good enough.

Late planting, poor stands, too much water, not enough water, this isn’t exactly a soybean crop sink a lot of money into.  However, some are wanting to put the virus out in fields where it doesn’t belong, because it is so much cheaper than a diamide.  Remember our recommendation is 3-5 small worms (less than ½ inch)/25 sweeps. I would feel ok having a few more worms than that, but they better be small. Remember this is a biological, not a traditional insecticide, don’t put it where it doesn’t fit.  Another note on the virus, it looks like getting good coverage is critical.  Several people have told us that they have seen a night and day difference between 3 GPA by air compared to 10 GPA by ground.

Redbanded stink bugs are being found here and there in the southern part of the state. But we haven’t heard of any fields being treated as of yet.  When it does become time to treat acephate + bifenthrin is the best option.  We’ve been told that acephate is in short supply so if you can’t find it then bifenthrin + imidacloprid, Endigo, and Leverage 360 are your next best options, in that order.

Optimum size bollworms for virus

Rice

Still seeing a healthy population of stink bugs in headed rice fields.  Once fields start drying down, stink bugs will begin to concentrate on the late planted rice.  Those fields have the potential to see some large numbers of stink bugs, so keep an eye on them.

We looked at a lot of row rice this year and we can find billbug in around half of them.  In some fields the damage looks pretty significant, in others its fairly sparse.  We have several trials out evaluating the efficacy of seed treatments on them and when to time an insecticide application.  Below are a few pictures of what they and their damage looks like. Sometimes we will find them buried up in the stem of a plant, sometimes they are in the ground below the plant. 

Dead tiller associated with rice billbug feeding.
Billbug larvae in stem.
Billbug adult feeding?
Billbug larvae at the base of rice plants in the soil.


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