Seed mixtures snarl pest control

U. ILLINOIS (US) — Increasing the use of seed mixtures in insecticidal corn is expected to increase risk and make pest monitoring more difficult.

“Seed mixtures may make insect resistance management (IRM) risky because of larval behavior and greater adoption of insecticidal corn,” says David Onstad, professor of crop sciences at the University of Illinois.

Also, block refuges present different risks because of adult pest behavior and the lower compliance with IRM rules expected from farmers.

Details of the research are published in the Journal of Economic Entomology.

“It’s likely that secondary pests not targeted by the insecticidal corn, as well as natural enemies, will respond differently to block refuges and seed mixtures,” Onstad says.

In corn-producing regions where target pests were once abundant, the risk management approach has provided tangible benefits. For example, Bt corn hybrids greatly reduced the number of European corn borers.

However, the risk management approach tends to ignore many aspects of insect pest management,” Onstad says, such as monitoring pest levels and concentrating treatments when or where appropriate, because of an assumption that most pests are controlled throughout the season, regardless of pressure levels.

“Although field corn has never been considered an IPM-intensive cropping system, there is less impetus than ever for growers or crop consultants to enter fields.”

Growers will also have fewer choices in what hybrids they grow in their fields. Experts in integrated pest management are concerned that some seed companies will provide fewer options for regional needs, secondary pests, disease control, and refuge plantings.

Researchers also question whether pyramided toxins will actually increase mortality in targeted pests.

“Without this increase in mortality through independent activity of each toxin, the pyramid has much less value for IRM,” Onstad says. The Environmental Protection Agency “recently acknowledged that a corn hybrid pyramided with two toxins active against corn rootworms does not significantly increase larval mortality.”

The new research is important as the industry transitions to the new paradigm of 95 to 5 seed blends across the Corn Belt, according to Mike Gray, an entolmologist with the University of Illinois Extension.

“A significant consequence of the seed mixture infrastructure emerging within the corn insect protection arena is increasing pressure on the long-term sustainability of the soil insecticide market,” Gray says.

“As the number of refuges configured as blocks, strips, or separate fields declines, soil insecticide use should also be reduced. Ultimately, loss of soil insecticide products will result in reduced flexibility of producers to effectively manage economic infestations of white grubs, wireworms, and other soil insects.”

Also, if resistance develops to Bt hybrids and becomes widespread, growers will need to have some remaining tools to manage insect pests of corn, Gray says.

“It remains to be seen whether some groups within the agribusiness sector will maintain their investments in this competitive arena just in case resistance develops or to offer products targeted against secondary soil insect pests.”

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