Farm Progress is part of the Informa Markets Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them. Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

For controlling Mexican corn rootworm: Rotation and technology crop keys

Benji Parham says farmers who don't adopt new technology will be left in the Texas dust, victims of low yields, weedy fields and insect-riddled crops.

“We have to be up to snuff on technology or we'll be left behind,” says Parham, a Moody, Texas, corn and wheat farmer.

Technology may be the key to solving one of his biggest challenges in corn production, the Mexican corn rootworm.

“If farmers in this area (South Central Texas) plant corn in the same field for three years in a row and don't use chemicals to control the Mexican corn rootworm, the crop will be devastated,” he says.

Parham follows a 50/50 corn and wheat rotation on his 2,000-acre farm to minimize Mexican corn rootworm damage. “With the corn crop, I still have to be careful,” he says. “We need insecticides.”

He's looking hard at seed treatments and is interested in transgenic varieties with activity against the Mexican corn rootworm and other pests.

Most corn farmers from the Northern Blacklands to the Gulf Coast of Texas, prime real estate for the Mexican corn rootworm, like Parham, understand the value of rotation, at least in theory.

Planting an alternate crop at least every other year would improve yield potential, break some weed infestation cycles and limit damage from the Mexican corn rootworm, their most damaging insect pest.

But theory pays few bills, leaving some farmers to rely on a corn monoculture and to find other ways to fight the Mexican corn rootworm.


Current options include seed treatments or in-soil insecticides, and growers will have biotech varieties available in 2004.

Parham has used soil-applied insecticides for years and says they do a good job, but the inconvenience and mess associated with planter box mixes convinced him to try a seed treatment three years ago.

“Prescribe was the only one available at that time,” he says. “The first year, we had only limited success because heavy rains after planting used up most of the chemical before it could do any good.”

The last two years have been better. “Prescribe worked very well two years ago and was nearly perfect last year.”

Parham also looks forward to genetically engineered varieties containing the YieldGard technology, including a Bt gene effective against the Mexican corn rootworm and other pests.

“I'll watch it the first year and see which varieties perform best,” he says. “Also, it has to be priced competitively. We still have to make a profit.”

The Mexican corn rootworm is not an isolated nuisance.

“Mexican corn rootworm is probably the most important insect pest facing corn growers in central Texas,” says Extension entomologist Allen Knutson.

Growing problem

“This is a growing problem,” says Glen Moore, Extension IPM Specialist for Ellis and Navarro counties. “With a good rotation program, especially with cotton, the pest was not much of a problem. But cotton root rot became more widespread, so cotton has less appeal and we have more corn. We've been seeing more Mexican corn rootworm infestations.”

Extension IPM specialist Dale Mott says the pest has become public enemy No. 1 for many Central and South Texas corn farmers.

“That's especially true in fields with continuous corn,” Mott says. “It has forced many growers, sometimes against their will, to rotate to other crops, which is a good idea anyhow.”

The problem, however, is finding an alternate crop that pays the bills.

“Rotation is the most effective control, but rotation is not always possible due to lack of suitable land,” Knutson says. In many areas, cotton is not an option and Moore says grain sorghum will not provide a return equal to corn.

Damage may be significant. “Mexican corn rootworm can cause total loss at times, especially during drought years when corn cannot re-grow roots damaged early by rootworms,” Mott says.

“I recently talked to one producer who said 80 percent of his corn was down because of Mexican corn rootworm damage,” Moore says. “He not only had yield loss but harvest was extremely difficult with stalks on the ground.”

Eggs overwinter

“Because eggs of the corn rootworm overwinter in corn fields, the risk of an economic infestation increases with the number of years the field is in continuous corn,” Knutson says.

Best control would be to rotate to a crop other than corn. “But if he can't do that, the next best strategy has been full label rates of proven insecticides,” Mott says.

Field history is important. “If the field had problems the previous season, a farmer can expect heavy Mexican corn rootworm populations if he plants corn the next year.

“The insecticides work,” he says, “but their residual (activity) plays out. Farmers plant (and apply insecticide/seed treatment at the same time) from mid-February through March. The Mexican corn rootworm eggs hatch around mid-April. The more insecticide remaining when the insects hatch, the better control farmers can expect. Unfortunately, most insecticides play out or are already gone around this time.”

Mott conjectures that the insects do not hatch all at once, but over a matter of weeks. “I suspect the ones that hatch later cause more damage and those that hatch earlier are more likely to be controlled by the insecticide.”

Knutson says seed treatments show promise. “Seed treatments are convenient to use. There is no need for calibrating insecticide boxes and grower exposure to insecticide is less.”

Parham says the heavy rainfall three years ago likely diluted the effect of Prescribe by the time the pests hatched. Last year, however, he planted later than usual and control was excellent.

“I think the seed treatment carried out 35 to 40 days and I don't recall seeing any Mexican corn rootworm damage.”

Parham likes the idea of having the insecticide on the seed. “I wish all the seed companies would coat corn seed, even if it adds another 30 cents or so per acre to costs. Seed treatments are much more convenient and much less messy.”

Moore says some growers have tried seed treatments in the past few years and have seen good results. But he doesn't believe a seed treatment compares with a full-label rate of a soil-applied insecticide in corn following corn.

“It's still too early to say definitively how well the seed treatments will hold up against Mexican corn rootworm,” Mott says. “I know seed treatments do well under light to moderate pressure, but I suspect, especially under very heavy pressure and non-favorable weather conditions, they will sustain more damage than some growers will tolerate.”

Lodging as tip-off

He says growers often realize they have Mexican corn rootworm problems only when they see corn lodging, generally around mid to late May. “Strong winds might push stalks over because rootworm damage prevented an adequate root system.”

Early panting may set up a corn crop for heavier Mexican rootworm infestations when protection from soil insecticide and seed treatments has run out.

“I've seen treated corn seed planted on March 1 completely lodged and next to it the same treated seed planted two weeks later with no adverse effects from the rootworms,” Mott says. “This holds for soil-applied insecticides as well. I have seen heavier root damage ratings in Mexican corn rootworm test plots planted earlier than in trials that are planted later in the season.”

The Mexican corn rootworm life cycle makes traditional control tactics more difficult.

“Mexican corn rootworms have one generation per year,” Mott says. “Adults lay eggs sometime after the corn begins to silk. Eggs remain in the soil until the following April, when they hatch.”

That's where farmers hit a Catch-22. In the Southern Blacklands, if the weather is mild, growers like to start planting corn as early as Feb. 10 and for sure by Feb. 25. But the earlier they plant, the less chemical protection will be available to control the Mexican corn rootworm when it emerges in mid-April.

On the other hand, the later farmers plant, the less yield they expect. Maximum yield potential begins to decrease around March 10.


That's where genetic engineering might be an answer. YieldGard technology provides expanded defense because the plant manufactures its own control toxins as it grows, so protection is not limited to a few weeks after planting

“Bt corn has just been labeled and will be available for the 2004 crop,” Moore says. “A good many farmers in this area are looking at it.”

He says field trials with Monsanto's YieldGard technology have been “as effective as full label rates of soil insecticides and cost will compare to those treatments. And we get a longer window of control.”

“I don't think planting date will make much difference in the level of Mexican corn rootworm control with the YieldGard technology,” Mott says.

Parham says he'll probably try the new varieties first on fields he likes to “micro-manage. I've used Roundup Ready varieties in similar situations and that may be a good place to start with YieldGard.”

Varieties with both YieldGard and Roundup Ready technology should be available for 2004.

e-mail: [email protected]

Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.