Monday, February 24, 2020

Army cutworms damaging wheat

A researcher at the Lubbock Center asked us to tell her what was eating up her ryegrass plots. Suhas Vyavhare and I checked the plots and some wheat fields near Lubbock and found abundant army cutworm larvae. The growth stages are varied from small to about one-inch, so there is plenty of damage yet to come.

Nebraska has a nice 2017 army cutworm alert that states the treatment threshold is four larvae per square foot (for grain production).  Our publication Managing Insect and Mite Pests of Texas Small Grains (page 8) says, "In outbreak years, fields can have 10 - 20 cutworms per square foot." What we saw today was not to that point, but it is still early and many larvae were small and hard to find. Typical damage includes chewing on leaves, cut plants and severed stems.

The first thing you will see when scouting is the leaf damage. During the day, the cutworms will be beneath the soil surface near the plants.

Army cutworm larva.

Clipped stem on 6-inch wheat plant.

Thursday, February 6, 2020

Know what you are buying in your Bt corn hybrids (including sweet corn)

The 2020 version of the Handy Bt Trait Table has just been published. This two-page quick reference guide lists the Bt and herbicide packages in all US field corn in an easy to follow manner. It also lists the pests the corn claims to control and those that have developed resistance to the trait packages. This year's changes include a discussion of finding European corn borer resistance to Cry1F corn in Canada. The table also now lists Bt toxins to which corn earworm (cotton bollworm) is resistant.

But wait, there's more! The first ever version of the Handy Bt Trait Table for Sweet Corn is now available as well. There are only a few Bt combinations available in sweet corn and the new table lists them all, including those for which resistance has been determined. Basically, only Vip3a sweet corn now provides good control of corn earworm in the south. The table lists all hybrids available in the US by company, hybrid and Bt type.

The Handy Bt Trait Tables for both field corn and sweet corn can be found here: https://www.texasinsects.org/bt-corn-trait-table.html

The following graph shows the number of corn earworm larvae per 25 ears of Bt and non-Bt sweet corn grown on the Experiment Station in Lubbock in 2019. It is easy to see that the older toxins are no longer working and in fact have many more larvae than the non-Bt types. (This is because the caterpillars are resistant to the older Bt toxins and also lose the behavioral tendency to cannibalize when on the Bts.) The graph also shows that Vip3a is doing a very good job of controlling corn earworm.