High corn acreage and herbicide resistance are affecting crops in the Mississippi Delta, according to research presented at the Agronomic Crops Field Day held at Mississippi State University’s Delta Research and Extension Center.

“We have been having some serious issues with plant bugs in cotton this year in some areas of the Delta,” said MSU Extension cotton and soybean entomologist Angus Catchot. “We’re not controlling plant bugs like we used to, and we’re looking at some really high numbers that have been sustained for a long period of time.”

Catchot cited high corn acreage as a top suspect for the increase in plant bugs. “The whole crop dynamic for us has changed in Mississippi,” Catchot said. “We’re looking at just under a million acres of corn in this state. Milo went way up, wheat went way up, and cotton went way down. We’re looking at a complete change in the landscape.”

Catchot said when sampling corn fields next to cotton in 2007, he found high plant bug numbers each time. However, the researcher said corn acreage does not explain the problem entirely.

“You go to the south Delta, where they have a lot more corn, and many have not experienced the exceptionally high numbers of plant bugs in cotton as other areas have,” Catchot said. “Corn is obviously a player, but it’s a lot more complicated than just corn.”

Other factors he suggested included a favorable spring for plant bug reproduction, adverse conditions for insecticide spraying, insecticide resistance and poor insecticide coverage.

DREC research plant pathologist Gabe Sciumbato said root-knot nematodes, microscopic underground worms that feed on the roots of plants, will increase in population because of the high corn acreage as well. “Corn is a good host for root-knot nematodes. As we start growing more corn over a number of years, we’re going to start building up our root-knot nematode populations.”

Sciumbato said root-knot nematodes feed on corn roots and the roots of crops rotated with corn, such as cotton and soybeans.

Another concern for agricultural production in the Mississippi Delta is the increase of weeds resistant to the herbicide glyphosate.

DREC rice weed scientist Jason Bond said that both glyphosate-resistant horseweed and volunteer Roundup Ready soybeans have become problem weeds for Mississippi rice production.

Bond’s recommendations for 2008 include using the herbicides Grasp or propanil plus Facet to control glyphosate-resistant horseweed and adding Valor to burndown programs for residual control. He also advised treating volunteer soybeans in rice early rather than pre-flood.

Glyphosate-resistant horseweed, ryegrass and pigweed are concerns in Mississippi Delta soybeans, said Tom Eubank, a DREC research associate.

For resistant horseweed in soybeans, Eubank recommended tillage, fall residuals, timely spring burndowns containing 2, 4-D or dicamba, or using Ignite at planting.

For resistant ryegrass, Eubank recommended fall residuals, a timely spring burndown mix including Select and then paraquat at planting.

In the case of resistant pigweed in soybeans, Eubank said recommendations include using residuals, tillage, alternate modes of chemistry and timely applications to prevent seed production.

Trey Koger, cotton weed scientist at the DREC, said a big concern on the horizon for Mississippi cotton is glyphosate-resistant pigweed.

“We can manage pigweed with residual herbicides,” Koger said. “Yes, it’s an added expense, but if we’re committed to growing cotton, we cannot continue to rely on glyphosate alone.”

Koger said he is currently screening pigweed species for resistance in the Delta from Tunica to Port Gibson.

e-mail: rwells@drec.msstate.edu