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Hessian fly strikes back!

Back in 2006 it appeared that Hessian fly was going to be the demise of no-till wheat production in Oklahoma. Early planting, lack of crop rotation, and no-till monocrop wheat all create a favorable environment for Hessian fly, and there were several early-sown fields that were completely lost to the Hessian fly in 2006 & 2007. About that same time OSU release a variety named Duster that was an excellent grazing wheat with good yield potential. Duster also happened to be Hessian fly resistant. (If you are not a Star Wars fan, skip the next sentence) This resistance was a clear proton torpedo in the thermal exhaust port of the fully operational Hessian fly Death Star.

Mature Hessian fly larvae are brown in color and often referred to as flaxseed. Tillers with larvae will not recover and will eventually die and slough off.

Mature Hessian fly larvae are brown in color and often referred to as flaxseed. Tillers with larvae will not recover and will eventually die and slough off.

Over the past four years, I have received very few calls about Hessian fly. It seemed as thought the adoption of Duster and unfavorable environmental conditions resulted in a dramatic reduction in Hessian fly in Oklahoma, but there are some indications Hessian fly is making a return. I have received a few calls about Hessian fly this fall, most of them from southwest Oklahoma. In most cases producers had  either switched to a newer variety that was not Hessian fly resistant or changed to a nonresistant variety because they were displeased with Duster’s performance the past two years.

There are no curative treatments for Hessian fly in wheat. If you currently have a field that is infested with Hessian fly, the first step is to assess the level of infestation. If a plant with four viable tillers has one infected, then the impact on yield might not be that great, as we could have additional tillering in late winter. A field with the majority of tillers infected is likely a good candidate for graze out.

It is never too soon to be thinking of how to limit the impact of Hessian fly on next year’s crop. Planting a resistant variety still remains the most effective technique of combating the Hessian fly menace in Oklahoma for dual-purpose wheat farmers. To determine which varieties are resistant, consult a current OSU Wheat Variety Comparison Chart. Insecticide seed treatments are effective early in the season, but do not typically last long enough to provide season long control in Oklahoma. Cultural practices such as crop rotation and delaying planting until mid October will also help reduce Hessian fly infestations but might not be suitable for all operations.

Insecticide-resistant greenbugs in TX Panhandle

By Tom Royer, OSU Extension Entomologist

I received some troubling news from the Texas Panhandle.  Dr. Ed Bynum, Extension Entomologist from Amarillo, reported finding some greenbug populations that were shown to be resistant to chlorpyrifos, the active ingredient in Lorsban 4E, and other generic products (Govern 4E, Hatchet, Nufos, Vulcan, Warhawk, Whirlwind).   You can read the full article by clicking on this url: http://texashighplainsinsects.net/april-12th-special-edition/  The bottom line:  he tested some suspect greenbug populations using a diagnostic test that he developed for testing greenbugs in sorghum in the 1990’s, and found that they were resistant to chlorpyrifos at labeled rates.

Greenbugs on wheat

Greenbugs on wheat

This should not raise panic among growers in Oklahoma for two reasons.  The first is that I have not heard of or received reports of any control failures for greenbugs in Oklahoma, in fact, generally greenbugs have been pretty scarce this winter.

The second reason is that it is late enough in the growing season to expect that the primary natural control of greenbugs, a tiny wasp called Lysiphlebus testaceipes (see picture to right), keeping greenbug numbers from becoming an outbreak.

Natural predators can keep greenbug infestations below economic thresholds

Natural predators can keep greenbug infestations below economic thresholds

The best course of action is to sample winter wheat fields with the Glance ‘n Go system.

Start by going to the Cereal Aphids Decision Support Tool on your computer http://entoplp.okstate.edu/gbweb/index3.htm and selecting the Greenbug Calculator.

By answering a few simple questions, you can determine an economic threshold for controlling greenbugs.  This threshold is based on the estimated cost of treating the field and the estimated price of wheat.  Once a threshold is calculated, you can print a Glance ‘n Go scouting form, take it to a field and record your sampling results.  The form will help you to decide if the field needs to be treatment for greenbugs.  There are several things that make Glance ‘n Go a good way to make such a decision. You only have to “Glance” at a tiller to see if it has greenbugs (no counting greenbug numbers).  You can make a decision to treat “on the Go” because you stop sampling once a decision is reached (no set number of samples).  Finally, you can account for the activity of the greenbug’s most important natural enemy, Lysiphlebus testaceipes.

Aphid Mummies (below)

When scouting with the Glance ‘n Go system, keep a running count of tillers that have aphid mummies and a running count of tillers that are infested with one or more greenbugs.  After each set of 5 stops, the Glance ‘n Go form directs you to look at your total number of infested tillers and tillers with mummies.  If there is enough parasitoid (mummy) activity, you will be directed to stop sampling and DON’T TREAT, even if you have exceeded the treatment threshold for greenbugs!  Why? Because research showed that at that level of parasitism, almost all of the healthy-looking greenbugs have been “sentenced to death” and will be ghosts within 3-5 days.  If they have received their “sentence” you can save the cost of an unnecessary insecticide application.

Treatment thresholds will probably fall around 2-4 greenbugs per tiller, but make sure you are using the Spring (January-May) form, not the Fall (Sept-December) form.  If a field needs to be treated, check with Current Report CR-7194, “Management of Insect and Mite Pests in Small Grains”.  If you treat for greenbugs and have a failure, please contact our Department and we will investigate further to determine