Friday, April 8, 2016

Corn Planting Decisions and Two New Publications That Can Help

There is still a lot of uncertainty about which crops to plant in parts of the southern High Plains of Texas. Cotton prices are down, sorghum faces a significant threat from sugarcane aphid, and corn requires more water than these other two crops. Many factors are involved in making planting decisions this year, and this article is strictly focused on the insect part of the equation, and the insect part is admittedly relatively minor as compared to available water, aphids and market prices.

Given that our pest pressure from caterpillars like the fall armyworm and corn earworm goes up as the season progresses, and that we have a range of Bt corn technologies with respect to their price and ability to kill these pests, there is room to save money on the front end of the season. Ed Bynum, Extension Entomologist in Amarillo, and I are suggesting that early planted corn can be non-Bt or one of the older and less expensive Bt technologies that has fewer toxins. On the southern High Plains, fall armyworm, not corn earworm, is the major threat to corn (see last year's post), and fall armyworm populations generally remain low until mid-season and then increase through the remainder of the season. Corn planted early in the planting window, and that planted in the first half of the normal planting window, stands a good chance of escaping significant fall armyworm damage. (Corn earworm is far less of a threat to corn in general because it is a tip feeder and does not puncture the sides of ears like fall armyworm.) If corn does need to be treated for fall armyworm, then we have two excellent insecticides available but they need to be applied in a window of six days centered around first pollen shed.

This being said about planting in the first half of the window, it also follows that corn planted in the second half of the normal planting window, and corn planted late, should have a very capable suite of Bt toxins if significant fall armyworm damage is to be avoided.

I should note that none of our Bt corn has any affect on spider mites, so the mite threat is the same on Bt corn as it is in non-Bt corn. Later planted corn is at less risk for significant spider mite infestations than is early and standard planted corn.

One final general statement is that there will be a lot of corn grown on the southern High Plains with reduced irrigation, and some with no irrigation. It has been demonstrated in many studies, including ours at Lubbock, that corn grown under moderate to severe drought stress is more prone to have high aflatoxin levels than corn grown with adequate water. Some people are saying that our very best Bt corn, because it has essentially no caterpillar damage, will not have aflatoxin. This is incorrect. Insects cause wounds where aflatoxin fungi can enter an ear, but even without such wounds there are many corn hybrids that can still get a lot of aflatoxin. This is a function of the genetics (susceptibility) of the hybrid as related to the amount of aflatoxin available in the system to colonize the plants at their susceptible stages. Yes, insect damage can make things worse, but no, there are no hybrids that won't get aflatoxin if the insects are controlled.

Now that I have presented the big picture I will get specific. Our newly revised "Managing Insect and Mite Pests of Texas Corn" has, for the first time, a list of recommended Bt technologies for the major caterpillar pests. These are all of the types of Bt corn that we know to be effective against a specific pest. Note that for fall armyworm the list is not as long as it would have been a few years ago; fall armyworm seems to be adapting to at least one of the older Bt toxins. To dive even deeper, the newly revised "Handy Bt Trait Table" lists the number and types of toxins in each technology. So when I say that more toxins are better, look in the Handy Bt Trait Table at the list of Bt toxins for each seed company's products. The newer and "better" (which is a relative term) Bt hybrids appear toward the end of the list of products within a seed company. Right now the very best protection against caterpillars comes from corn that contains Vip3a in combination with other toxins.

The Handy Bt Trait Table and Managing Insect and Mite Pests of Texas Corn are meant to be used together. We are indebted to Dr. Chris DiFonzo at Michigan State University for allowing us to create a southern version of her very popular Handy Bt Trait Table for the corn belt. Our version is for the cotton growing regions that have larger mandated refuge requirements than in the corn belt. All we did was take Dr. DiFonzo's publication and change the refuge requirement column. Her original version for the corn belt and counties at the top of the Texas Panhandle is here: http://msuent.com/assets/pdf/28BtTraitTable2016.pdf .