IF YOUR FIELDS are under attack from tough-to-control weeds, don't look for a cavalry of new herbicides to come to your rescue any time soon. In fact, only one new active ingredient is expected to enter the corn and soybean marketplace in 2006, along with a handful of premixes and me-too products.

Because development of a new product costs $150 million to $200 million and thin profit margins exist, companies have little incentive to invest in new active ingredients, especially in the soybean market, notes Aaron Hager, University of Illinois Extension weed scientist. Those harsh facts, he says, simply underscore the need for growers to preserve the weed-control efficacy of existing active ingredients, namely glyphosate.

Unfortunately, in soybeans, at least six weed species now exhibit some level of resistance or tolerance to glyphosate: marestail (horseweed), common ragweed, Italian ryegrass, rigid ryegrass, Palmer pigweed and several lambsquarters biotypes. In addition, this past fall Monsanto and weed scientists at the University of Missouri — Columbia identified a potential case of glyphosate-resistant waterhemp in the northwest part of the state.

To preserve glyphosate, now used in corn as well as in soybeans, weed-control specialists continue to encourage growers to focus more attention on implementing good stewardship practices, including the use of crop rotations, soil-applied products and, whenever possible, a different active ingredient.

Here's a brief look at the new corn herbicides available for the 2006 season.

Impact

This new postemergence herbicide from Amvac Chemical Corporation offers broad-spectrum control of key broadleaf weeds in corn. The active ingredient is topramezone.

This low-use-rate systemic herbicide offers crop safety for all types of corn. In addition to field corn, it is labeled for use on more sensitive corn types, including seed corn, sweet corn and popcorn.

Bill Jacobs, Amvac Midwest regional manager, says the herbicide fits a wide range of weed-control programs in conjunction with most soil-applied and postemergence corn herbicides.

Impact can be applied any time after corn emergence until 45 days before harvest. Optimum application timing is when broadleaf weeds are 2 to 5 in. tall and before they compete with the crop.

Impact can be applied sequentially following preplant or preemergence herbicide applications. It also is compatible for tank mixing with postemergence herbicides labeled for use in corn and is labeled for use on Roundup Ready and LibertyLink hybrids. In addition, it can be tank mixed with residual herbicides in one-pass early postemergence programs for burndown of emerged grasses and broadleaf weeds.

Impact controls velvetleaf, cocklebur, pigweed, common and tall waterhemp, lambsquarters, kochia, sunflower, common and giant ragweed, and nightshade.

The herbicide also offers a bonus: GrassAssist control and suppression of important grasses. At the recommended rate of 0.75 fluid oz./acre, the herbicide controls giant foxtail, large and smooth crabgrass, barnyardgrass and goosegrass and offers partial control of green and yellow foxtail, seedling johnsongrass, fall panicum, wild proso millet, broadleaf signalgrass and woolly cupgrass.

In most cases, Impact will be used in combinations with reduced rates of atrazine, which increases the speed and the degree of weed control and adds a second mode of action. For most applications, between corn emergence and until it reaches 12 in. tall, the company recommends using atrazine at 0.5 lb. of active ingredient/acre.

Impact is packaged in quart containers containing 30 fluid oz. to treat 40 acres at the labeled use rate. When applied by ground, the recommended minimum water carrier volume for Impact is 10 gal./acre. The addition of methylated seed oil or crop oil concentrate and nitrogen fertilizer, as spray additives, is recommended to achieve optimum weed control.

Growers will be able to rotate to major field crops, including all corn types (anytime), cereal crops (three months) and alfalfa, cotton, peanuts, potato, sorghum and sunflowers (nine months). The rotation interval for soybeans also is nine months in the central and southern Corn Belt.

In the northern Corn Belt, the rotation interval for soybeans is 18 months at the 0.75 fluid oz./acre use rate. There will be 2(ee) recommendations that will allow a nine-month rotation interval for soybeans following Impact use at the 0.5 fluid oz./acre use rate, in Michigan, Minnesota, Wisconsin and the northern parts of Iowa, Illinois and Nebraska.

Impact herbicide can be used sequentially following soil-applied insecticides or in combination with foliar-applied insecticides registered for use in corn.

Impact is the first new herbicide for the corn market introduced by Amvac, a subsidiary of American Vanguard Corporation. In the corn market, the company is known for its SmartBox closed-handling system, which provides precise application of corn rootworm insecticides while reducing applicator exposure.

Radius

The EPA granted registration for Radius in April 2005, too late in some instances for growers to purchase and use this new premix from Bayer CropScience.

The herbicide, which combines two soil-applied active ingredients (flufenacet and isoxaflutole), offers growers one-pass weed control, says Andrew Seitz, product manager. (See related story, page 47.)

Resolve DF

DuPont Resolve DF is designed to improve corn growers' weed-control results in a Roundup Ready program. This corn herbicide was registered for use last year in the western United States and is now available in the Midwest for 2006.

When tank mixed with a glyphosate herbicide, Resolve DF provides burndown and/or residual activity on later-emerging grasses and broadleaf weeds, as well as control of many troublesome weeds that glyphosate alone currently misses, according to Jim Flater, DuPont product manager. These include wild proso millet, common lambsquarters, hairy nightshade, pigweed species, common purslane and seedling Russian thistle.

A Resolve/glyphosate tankmix can be applied, along with a nonionic surfactant and an ammonium nitrogen fertilizer, to glyphosate-tolerant field corn up to 12 in. tall.

Russ Martin, crop consultant at Servi-Tech, Colby, KS, evaluated Resolve/glyphosate on no-till corn last season. “We were looking for longer-lasting activity on problems including shattercane and palmer amaranth,” he says. “The control was very good and held until the crop canopied. What really impressed our growers is that they received a residual herbicide for roughly one-third the price of competitive programs, plus saved the cost of repetitive trips.”

First Act, Double Team and Parallel Plus

The EPA recently registered three preemergent herbicides from MANA for use in corn. MANA, which specializes in generic crop protection products, reports that it is the first generic-products company to obtain a comprehensive registration for acetochlor, to be marketed under the brand name First Act. Other new registrations are Double Team, which is a premix of acetochlor plus atrazine, and Parallel Plus, a premix of metolachlor, atrazine and benoxacor safener. MANA is the North American subsidiary of Makhteshim Agan Industries Ltd.

NEW, FALL-APPLIED HERBICIDE

SOYBEAN GROWERS will find one new product available for weed control. DuPont Canopy EX is a new fall-applied soybean product designed for control of many winter annuals and certain perennials, plus residual control that results in cleaner fields at planting.

According to Jeff Carpenter, DuPont soybean product manager, the herbicide is an ideal setup for spring planting in no-till soybean acres. “They can start off their new crop with a cleaner, warmer, drier field in the spring,” he says.

Carpenter says a fall application, immediately after harvest until ground freeze-up, provides burndown and residual control through planting of lambsquarters, common chickweed and giant ragweed. For optimal results when applying Canopy in the fall, a producer should spray before winter annual weeds exceed 1 to 3 in. in diameter or height. Control depends on the rate used, weed spectrum and size, along with growing conditions.

Bill Johnson, Purdue University weed scientist, says he has seen excellent performance from Canopy EX in Indiana on winter annual weeds, such as chickweed, henbit, marestail and dandelion.