There's been much hype in recent years about the coming introduction of transgenic corn hybrids with built-in rootworm protection. Most corn growers can hardly wait.

Even when given EPA approval, however, rootworm-resistant corn will likely be in short supply at first. In the meantime, most farmers continue to rely primarily on soil-applied insecticides to rout rootworms.

However, some growers are trying seed treated with an insecticide such as Force ST, a Syngenta product applied with ProShield technology, or Prescribe, from Gustafson LLC.

University entomologists generally advise producers to go with soil-applied products as the better way to combat rootworm wreckage. Their research has largely shown that the soil insecticides, with one or two exceptions, provide greater root protection and better root ratings than does seed treatment.

University of Illinois trials at Urbana, Dekalb and Monmouth have shown that the majority of soil insecticides have posted better root rating scores than did hybrids treated with Force ST or Prescribe. However, the Force ST- and/or Prescribe-applied hybrids outperformed some soil insecticides on root ratings in one or more of the locations.

In Iowa State University trials, the Force ST and Prescribe seed treatments have not performed well compared with soil-applied insecticides. They have not consistently protected roots from corn rootworm injury, especially if the field had a moderate to large rootworm population, according to Iowa State research.

“I think seed treatments have real potential,” says University of Illinois entomologist Mike Gray. “We still have much to learn, however.”

But some seed companies offering seed treatments maintain that root ratings don't tell the whole story. They say yield, not root ratings, is the bottom line.

Syngenta Seeds, producer of NK Brand hybrids, says its in-house testing shows that Force ST-treated hybrids produce yields equal to the same hybrids using a soil insecticide. The company also cites favorable 1998-2000 comparisons by seven university and private researchers, completed at 25 locations. Those trials compared root ratings (on a scale of 1 to 6, with 1 indicating no damage and 6 indicating severe damage) and yields for Force ST hybrids, plus the same hybrids treated with Lorsban 15G, Aztec 2.1G, Counter 15G and Force 3G. There also was an untreated check.

The hybrids receiving a soil insecticide had root ratings ranging from 2.1 to 2.6. Force ST hybrids averaged 3.1. The untreated checks averaged 4.4.

Yields for soil insecticide-treated and Force ST hybrids all were virtually the same — in the 138- to 142-bu/acre range. The untreated checks averaged 123 bu/acre.

“Although yields may have been similar, yield can be affected by many factors,” counters Gray. “That includes moisture levels after rootworm damage, overall plant stress and the genetic ability of a hybrid to recover yield-wise from root damage. Our research is intended to rate the amount of root damage under different treatments. We cannot predict what will happen after rootworms finish their feeding.”

Scott and Steve Gilmore, corn and hog producers, Compton, IL, raise largely continuous corn to meet feed needs. That usually means a battle with rootworms.

“But we don't like handling an insecticide,” says Scott. “So three years ago (2000), we compared ProShield hybrids to Furadan and to untreated strips. The ProShield corn and the Furadan-protected corn had satisfactory root protection and good yields while the untreated strips were a disaster.

“We have planted several hundred acres of ProShield hybrids the past two years,” says Scott. “In 2002, three ProShield fields had root ratings of 1.2, 2.3 and 2.3, respectively (scale of 6). A Furadan field had a 2.9 rating. All were long-term continuous corn. The ratings were done by our independent crop consultant.” (Yields from those fields were not yet available at presstime.)

NC+ Hybrids, Lincoln, NE, offers both Prescribe- and Gaucho-treated seed to growers. “We want to provide customers with an alternative to handling insecticides,” explains Ken Anderson, marketing manager.

The company does not make yield claims for either product. Rather, it states that Prescribe offers protection from low to moderate levels of corn rootworm, and also controls wireworms, flea beetles (through the five-leaf stage) seed corn maggots, white grubs and other planting time insects. They say Gaucho (a less potent form of Prescribe) protects against wireworms, flea beetles (up to one-leaf stage), seed corn maggots, imported fire ants and other planting time insects.

NC+ also points out that Gaucho often improves overall plant health and vigor in the spring (see above story).

Gustafson, manufacturer of Prescribe and Gaucho, will soon introduce a new product, clothianidin, to replace imidacloprid, the active ingredient in Prescribe and Gaucho. (Gustafson refers to the technology as “seed-applied insecticide.”)

“The lower rate of clothianidin will control all pests now handled by Gaucho, plus cutworms,” reports Paul Holliday, product manager. “The higher rate, analogous to Prescribe, will control all levels of rootworm density, not just low and moderate populations.

“We see clothianidin as the next generation of seed treatment,” says Holliday. “It increases the number of insects controlled and the level of effectiveness.”

Gustafson officials say that, if all goes well from a regulatory standpoint, some clothianidin-treated seed could be available for 2003 planting.

Gaucho Gusto?

Although Gaucho seed treatment is intended to combat such insects as wireworms, seed corn maggots and imported fire ants, it may have yield-enhancing qualities not directly tied to insect protection.

Tim Maloney, an independent researcher and owner of Agri-Tech Consulting, Janesville, WI, has been comparing Gaucho-treated seed with untreated seed (same hybrid) since 2000 in corn after corn. He fills half his planter with treated seed, half with untreated. Maloney has done the testing at several locations with numerous replications.

Although he's observed no obvious insect activity in his trial fields, the treated seed has improved stands by 8-10%, Maloney notes. Yields of the treated seed have usually been 4-5 bu/acre higher, sometimes more.

“I can only report the results,” says Maloney. “I can't say for sure whether the improved performance is due to a stronger defense system, more vigorous growth or something else.”