Insect Strip

Insect Strip

Tuesday, March 8, 2016

Wheat Pest Report

Army cutworm
Last Friday, I received a call from Scott Strawn, CEA - Ochiltree County, reporting army cutworms were found in a producer’s wheat field. The cutworm larvae hide in loose soil at the base of the plant or under soil clods on sunny days. Then at night or on cloudy days will come out and can be found feeding on the plants. They clip the above-ground portion of the plant from the root system at or below the soil surface.  When disturbed larvae will curl into a “C” shape. Infestations will be “clumped” across the field resulting in sporadic dead spots. These infestations are from the moths laying eggs in the soil last fall and then larvae hatching following our rains from September to November. Current suggestions for control is when there are 4 or more larvae per square foot. But, when plants are small coming out of dormancy or under moisture stress then 2 or more larvae per square foot may require a treatment. Any of the pyrethroid insecticides labeled for army cutworms should provide effective control.

Photo: Kansas State University Extension Entomology
winter Grain Mite

Dr. Charlie Rush, Research Plant Pathologist, Texas A&M AgriLife at Bushland called this morning about little reddish mites in a dry area of his wheat field. The mites are the winter grain mites,  Penthaleus major (Duges). They can be a pest of wheat, barley, oats, and rye. The distinguishing characteristic is that all life stages have reddish-orange legs and a red spot on the abdomen. The body of the immatures are dark brown while the adult body may also be black. All of the legs are equal in length which differs from the Brown wheat mite that has the front legs 2X longer than the other legs. Their activity declines after temperatures exceed 75oF because at these temperatures the eggs do not hatch but over summer until the fall. They feed primarily at night or during cloudy conditions. Damage symptoms begins as speckled yellow spots on the leaf (similar to spider mite damage to corn leaves) but progresses as tips of leaves turning brown, plant stunting with a silvery-grey appearance and even plant death. No thresholds are available for making control decisions. So, control becomes a judgement between how extensive the damage becomes and when temperatures are high enough to cause mite numbers to decline. Also, because the winter grain mite is such a minor pest there is only Malathion 5E at 2 pt/A labeled for control.
Winter grain mite, Photo: Kansas Department of Agriculture
Aphids
Now would be a good time to begin scouting for greenbugs (GB), Russian wheat aphids, and bird cherry-oat aphid (BCOA). Greenbugs and bird cherry-oat aphids are known to be vectors of the barley yellow dwarf virus. Unlike the greenbug, the bird cherry-oat aphid does not inject a toxin while feeding and therefore feeding by this aphid is less damaging, but still can cause significant yield loss. Recent studies by Oklahoma State University and the USDA-ARS has shown a 5% loss in yield when there are 20 BCOA per tiller for 10 days before the boot stage and a 9% yield loss at 40 aphids per tiller for 10 days. Both the greenbug and the bird cherry-oat aphid co-exist and feed on the underside of the lower leaves. Unlike GBs, feeding from BCOAs does not cause visible damage to wheat plants. GB feeding appears as yellow or reddish-brown irregularly shaped spotting  on the leaves and will progress to cause yellow or large dead areas across the field. Russian wheat aphids feed in rolled leaves on the upper part of the plant and injects a toxin that causes purple and white longitudinal streaking on the leaves. Decisions to treat for both the GB and the Russian wheat aphid should be based on established economic thresholds which can be found at previously posted article on the Texas Panhandle Pest News (http://txppipm.blogspot.com/2015/03/texas-high-plains-wheat-pest-update.html).
Chlorpyrifos Status
On October 30, 2015, EPA proposed to revoke all food residue tolerances of chlorpyrifos in response to a court-ordered deadline by the 9th Circuit Court of Appeals. EPA notified the court that the final rule will occur in December 2016.  So, what would be affected by this proposed rule on chlorpyrifos. If this moves forward as outlined then all agricultural uses of chlorpyrifos would end in December 2016. Currently, chlorpyrifos remains registered and can still be used this year as specified by the product label. Insecticide companies are still able to sell chlorpyrifos products for agricultural use this market year.