Oct 7, 2008
Specialty Crops get Short Shrift in Weed Control

If herbicides were a meal, the major commodity crops – corn, soybeans, rice, wheat, cotton – would be enjoying a gourmet feast, while fruits, vegetables, nuts and ornamentals would be lucky to get the scraps from the table.

That’s one assessment shared by a handful of papers in the April-June 2008 issue of Weed Technology, a publication of the Weed Science Society of America (WSSA).

Weeds are almost always the No. 1 pest problem in cropping systems – especially organic cropping systems. About two-thirds of the pesticides applied on all crops are applied to control weeds, said Lee Van Wychen, WSSA’s director of science policy.

WSSA, a nonprofit organization that promotes awareness of weeds and invasive plants, has 1,400 members, mostly in the United States and Canada. The membership is made up of university and Extension personnel, state and federal employees and specialists in the private sector, Van Wychen said.

Herbicides play an essential role in weed control, and because they target pathways that typically have no relation to humans, they are safer than insecticides or fungicides. Developing and launching an herbicide with the right selectivity, however – one that won’t damage the crop you want to protect – can be a challenge, Van Wychen said.

“It’s hard to separate the good plants from the bad plants.”

Research is needed to find the use rates that will kill weeds but not crops – and research costs money and time. For herbicide manufacturers, commodity crops offer a safer return on their investments of money and time than specialty crops.

According to two of the Weed Technology papers – “The Challenges of Specialty Crop Weed Control, Future Directions,” by Steven A. Fennimore and Douglas J. Doohan, and “Industry Views of Minor Crop Weed Control,” by Roger E. Gast – registering a single herbicide for a single crop planted on millions of acres is easier and cheaper than registering dozens of herbicides for dozens of crops planted on thousands of acres each.

“Economics dictate registration efforts only toward crops that will create a significant, positive return on investment,” according to Gast’s paper. “In most cases, development of new herbicides for minor crops is not economically viable due to low or negative return on investment and disproportionate liability risk.”

There’s more than one definition of a “minor” crop, but EPA defines it as anything grown on 500,000 acres or less. That would include most specialty crops, including fruits and vegetables, said Gast, a weed scientist and the product development leader at Dow AgroSciences.

Minor crops are rarely considered during the discovery and initial development phase of an herbicide, which focuses almost entirely on major commodity crops. If minor crops are considered at all, it’s in the later stages of a product’s life cycle, according to Gast’s paper.

Because of that lack of attention, minor crop producers are forced to rely on a small cadre of old herbicides with limited weed control spectrum, combined with mechanical cultivation and labor for hand weeding. To make things worse, regulatory action has severely restricted many of those old herbicides. Some of them have been removed from the market altogether, according to Fennimore and Doohan’s paper.

When an herbicide is removed from the market, there’s often little or no attempt by the manufacturer to defend the product, because there is little economic incentive to do so. The fear of liability drives many of the decisions to give up the fight, according to the paper.

“Often, a single liability claim or threat of such is sufficient for a registrant to withdraw a particular use,” wrote Fennimore and Doohan.

Specialty crops are more expensive than commodity crops, a fact that adds to the liability risk. Damaging an acre of strawberries worth $30,000 could cost a manufacturer more than damaging an acre of corn worth $600, Gast said.

Getting it right

Herbicide testing on specialty crops is usually conducted by university and Extension researchers, Gast said.

“Many times, we are relying on the public sector to generate crop selectivity data for us,” he said. “Public research helps defray the cost of us doing it ourselves.”

Public research might be cheaper, but the manufacturer still has to decide if the research is reliable, Gast said.

“On an everyday basis, we’re approached by university folks or commodity groups, asking if we would register one of our products on their crop,” he said. “The rub comes when somebody asks us to register on a crop that only has a thousand acres in the United States. We have to decide whether the risk is worth the reward.”

Gast said there were some registrations that, in retrospect, his company would never have approved had it known what the outcome would be. Every once in a while, however, an herbicide ends up working well on certain specialty crops, even though it wasn’t originally designed with them in mind. When that happens, it’s “gravy” for the manufacturer, he said.

The weed scientist used Goal as an example. The herbicide and its variants are registered on a number of specialty crops, even though Goal’s success in that market was more or less an accident.

Rohm and Haas initially developed Goal about three decades ago. The herbicide was acquired by Dow AgroSciences in 2001, along with the other products in Rohm and Haas’ ag division (Dow bought the rest of Rohm and Haas earlier this year, Gast said). When first developed, Goal was intended for major crops like soybeans and peanuts, but designers found it didn’t work as well as they had hoped. When they looked closer, however, the designers discovered that Goal had potential in the specialty crops market, according to Gast.

“They made some good lemonade out of some lemons.”

Indeed, they made a product that has been consistently competitive in the U.S. specialty crops market for more than 20 years, a product that’s registered on a variety of crops including almonds, pistachios, walnuts, peaches, apples, cherries, pineapples, broccoli, cauliflower, cabbage, onions, artichokes, etc., Gast said.

“For many years, IR-4 has come to Rohm and Haas and Dow, asking for new uses for Goal in minor crops,” he said. “We’ve worked with them on most of those requests.”

(IR-4 is the federal program that develops and submits regulatory data to support the registration of pest control products for specialty crops.)

After acquiring Goal, Dow decided to develop new formulations: Goal 2XL and GoalTender. Goal 2XL is an emulsifiable concentrate herbicide that is more user-friendly. GoalTender, a water-based formulation, works well when applied post-emergence on some vegetable crops, Gast said.

“With Goal 2XL, you’re maximizing product performance,” he said. “With GoalTender, you’re getting a product that’s more environmentally friendly.”

Fennimore, an Extension vegetable specialist with the University of California, Davis, studied Goal’s effects on specialty crops in California. In an e-mail, he said Goal’s success is a combination of luck and Dow’s willingness to go after small markets like the vegetable market.

“Dow uses a niche market strategy that I wish every chemical manufacturer used,” he wrote.

Goal is effective because it controls key weeds like little mallow, which can’t be controlled by fumigants in strawberry or by other herbicides in cole crops. GoalTender can be sprayed over the top of broccoli and cauliflower.

Another advantage of Goal is that it has some soil residual that can be controlled by adjusting the rate. Many herbicides have too much soil residual activity and too many rotational restrictions that would keep them out of California’s vegetable markets, according to Fennimore.

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