Forrest Laws 1, Director of Content

December 10, 2008

5 Min Read

Farmers like to have their farms look nice. They mow the turn rows or spray herbicides around ditch banks or even hire crews of teenagers to chop escaped weeds out of their fields during the growing season.

But cotton producers may be able to further improve the aesthetics of their operations — and save some money on insecticide bills — by extending those clean-up efforts to late winter and early spring, a university entomologist says.

Jeff Gore, assistant professor at Mississippi State University’s Delta Research and Extension Center, says growers can help reduce the numbers of tarnished plant bugs moving into their fields during the growing season by eliminating wild host plants in late February through early March.

Gore reported on his observations, which are based in part on the work of USDA entomologists Gordon Snodgrass, William Scott and Craig Abel, during a presentation at Cotton Incorporated’s Crop Management Seminar in Robinsonville, Miss. His presentation was titled, “Landscape management to reduce tarnished plant bugs in cotton.”

“When we talk about landscape management for plant bugs, it’s really more than just within the cotton crop season,” says Gore. “We can do a lot of things throughout the entire year. But we need to know when these plant bugs occur.”

Gore was addressing an issue that is expected to garner increasing attention this winter: How to keep the cost of growing a cotton crop from spiraling even higher.

As Kelly Bryant, an agricultural economist and director of the University of Arkansas’ Southeast Research and Extension Center, noted, gross revenues are forecast to be higher for cotton than for any other crop in the Mid-South. But cotton also has the highest variable costs.

Since cotton prices seem stuck below the Commodity Credit Corp. loan rate of 52 cents per pound for now, figuring out how to keep from spending $100 per acre or more on insect control may be a key ingredient for preventing cotton acreage from dropping even further in 2009.

Many cotton farmers spray or mow vegetation along field borders to try to reduce plant bug numbers before they can move into squaring cotton. But most of that takes place during the early part of the growing season.

“From the landscape management standpoint, I think we can break the year up into three segments: Late winter into early spring; then summer, the crop season; and the fall to early winter, when plant bugs are going into reproductive diapause,” says Gore. The latter is the weak point in their life cycle, he notes.

Sampling conducted by the USDA researchers has shown tarnished plant bugs can be found on more than 350 species of wild host plants. In early spring, those can include buttercup, evening primrose, butterweed, annual fleabane, sourdock, vetch, crimson clover and cutleaf primrose.

The researchers conducted an area-wide plant bug management study that involved an application of a selective herbicide to remove winter vegetation at a time when plant bug numbers typically decline.

“They looked at making a single application of a herbicide in March to selectively control broadleaf weeds and leave the grasses behind,” Gore said. “The herbicide was Strike 3, a combination of 2,4-D, dicamba and mecroprop, which does a good job of controlling emerged winter annuals and suppressing the seed germination of some of the summer annuals.”

The researchers found that tarnished plant bug numbers were higher in the untreated areas of the Delta throughout the growing season compared to locations that were sprayed with Strike 3 to control the wild hosts in March.

“In the study in 1999 through 2001, we averaged saving about one plant bug application in the Delta each season,” he said. “This is important because for every insecticide application we eliminate we have the potential of reducing the selection pressure we’re putting on our plant bugs. There could also be a big impact from the economic standpoint now and in the future.”

An analysis by Mississippi State University economists indicated savings of an average of $5.90 per acre above the cost of spraying the herbicide. (The researchers sprayed only about 4 percent of the land area, resulting in considerable savings in the application of a relatively expensive herbicide.)

“Plant bugs can build up to tremendous numbers in a relatively small area along road side ditches compared to an area that has been treated with a herbicide,” Gore notes. “Some plant bugs will survive on the grass that has been left in these herbicide treatments, but they won’t increase their populations the way they will in the untreated areas.”

He cautioned growers about applying non-selective herbicides such as glyphosate because of resistance issues and because the grasses can help suppress summer annuals such as pigweed that can infest their fields.

Gore displayed a now-infamous picture of a cotton field in which one side has been decimated by plant bugs moving into the field from an adjacent corn field. “We saw similar effects with soybeans in fields adjoining cotton in 2008.”

The fall and winter months — the time when plant bugs are entering reproductive diapauses — can also offer opportunities for reducing plant bug numbers.

“This time of year when plant bugs are going into diapauses is marked by a general decline in the overall population,” says Gore. “I think this is a time when we can kick them when they’re down so to speak.”

Temperatures have little impact on plant bugs — the insects can over-winter as far north as Canada. And certain winter weeds, specifically henbit, seem to be more accommodating to enable plant bugs to reproduce.

In research conducted by Gordon Snodgrass, a certain percentage of the population seemed to remain reproductive for a much longer time period when the pests were found on henbit rather than ground trash or other wild hosts.

“When you look at the occurrence of plant bugs on these winter hosts, specifically henbit, we start seeing plant bug nymphs much earlier in the year, about the third week in January, compared to these other hosts,” said Gore.

He said he’s planning to begin looking at the impact of fall burndown programs, residual herbicides and tillage to remove those plants. “Just about every field that doesn’t have a fall burndown or tillage program is covered with henbit. So if they’re starting to get nymphs the third week in January, we may need to do something to remove this host.”

e-mail: [email protected]

About the Author(s)

Forrest Laws 1

Director of Content, Farm Press

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