What’s New In Fruit And Nut Weed Control

Kelli Woodwick

Other impediments to crop production might garner more headlines — such as the latest invasive insect — but year in and year out, weeds continue to cause growers a lot of headaches. For this first of our four-part series on crop protection, we talked with representatives from a couple of companies that are focusing on solving problems with weeds. One is Kelli Woodwick of Valent USA, brand manager for Chateau (flumioxazin), which has added a number of new uses for the coming season. The second, Pam Marrone, CEO of Marrone Bio Innovations, takes a biological approach to weeds.

Q: What are the biggest challenges fruit growers are facing regarding herbicides these days? Please be as specific as possible.

Woodwick: U.S. tree fruit growers tell us that in making herbicide choices they must consider compliance with various regulations, including groundwater, surface water run-off, and air (Volatile Organic Compounds, or VOC), to name a few. They also have challenges with international regulations related to maximum residue levels (MRL) which can limit their choices of products to use.

In addition, orchards are having the unfortunate challenge of herbicide resistance. As you know, growers are very smart at overcoming challenges. What they have found is that an application of a solid pre-emergent herbicide, such as Chateau or another residual herbicide, puts them back in the driver’s seat. Early control with an alternate mode of action will keep this growing challenge in check.

Marrone: What you have to understand is that glyphosate (Roundup) was almost too effective. It was so effective that companies actually stopped their herbicide development programs. But then with Roundup/glyphosate used for so many years so intensively on so many acres of Roundup-ready crops, resistance is going to happen. Our R&D is trying to fill the gap by screening microbes that produce natural products with novel modes of action. For organic, we tried to fill the gap with a burndown product, GreenMatch, but it just didn’t pencil out for the average grower, who only budgets $50 to $70 per acre for herbicides.

The other major challenge is there are few pre-emergent products. There really is a need. We have one that is supposed to be registered in April that is currently called MBI005. Used pre-emergent, it is broad spectrum. Post-emergent it’s selective and kills broadleaf and sedges. It’s a new mode of action, one of the first in 20 years. Initially it will just be used by organic growers because of the price, but then when we optimize fermentation over time the price will come down. It also synergizes conventional chemical herbicides, so we will see it used in combinations. We have another herbicide (systemic) in development. It’s a new species of bacterium that was discovered in a Buddhist Temple garden in Japan by one of our employees. The key for us is developing a good formulation to move the compound produced by the bacteria into the plant.

Q: Have any weeds emerged in recent years that are particularly thorny challenges for fruit growers?

Woodwick: Yes, there are some thorny weed challenges, both literally and figuratively. We have heard from many growers how difficult it is to control emerged marestail (horseweed), fleabane, and Italian ryegrass. University researchers throughout the U.S. do a fabulous job of identifying emerging weed challenges and test current and new herbicides to find the best herbicide control program.

Marrone: Marestail, also called horseweed, and fleabane. In almonds, rigid rye grass is a becoming a real problem. As I said, growers need new products. There will be a lot of new biological pesticide products coming along. In biologicals, 20 years ago the focus was on mycoherbicides, products with a fungus that kills weeds. But the problem was they could only kill one weed at a time. But now there are broader spectrum products coming onto the market in the next one to two years that can be used by organic growers to either stand alone and in combination with chemicals.

A fungus, Phoma, discovered by Agriculture Canada, which is like the Canadian USDA, looks promising. In the future such a bioproduct can be combined with small amounts of chemicals, mitigating regulatory issues. We see mixtures of chemicals. Why not mixtures of biological active ingredients and mixtures of biological and chemicals? We are mixing and matching so the biologicals of tomorrow will have broad spectrum impact.


Q: Does glyphosate (Roundup) resistance continue to be a problem? With what weeds? In what fruit crops? What can fruit growers do?

Woodwick: Yes, you are right, Roundup, or its active ingredient glyphosate, does have challenges with resistance. The thorny weeds we just talked about have glyphosate resistance: marestail (horseweed), fleabane, and Italian ryegrass. In the past these weeds were more easily controlled by glyphosate. While glyphosate has a good fit in weed control, it now benefits from the support of other herbicides to get after these tough weeds early. As mentioned earlier, an herbicide program approach will benefit all growers by limiting the spread of these tolerant weeds.

Marrone: Yes, the weeds I mentioned earlier are all especially problematic because of Roundup resistance problems. You don’t have the resistance in fruit-growing regions like California as bad as in the Midwest or Southeast where Roundup-ready crops are prevalent, but still for marestail, fleabane, etc. growers are desperate for new modes of action.

Many are starting to go back to using old chemistries. In the Midwest they are going back to older once-popular chemicals such as 2,4-D and dicamba. Also, there’s a lot more mechanical cultivation going on.

Q: Has your company come out with any new herbicides and/or label additions?

Woodwick: Thanks for asking, yes, Chateau has proven to be a great offense in the battle to get the upper hand on marestail, fleabane, and about 90 other common weeds in orchards. I am excited to share that recently we added Italian ryegrass to our list of weeds controlled by Chateau. We also expanded the tree nut label to allow in-season, after bloom, low-rate applications of Chateau in combination with a post-emergent herbicide.

In 2012, IR-4 and Valent will submit for EPA registration two new orchard crops, pomegranate and olive. Both of these crops fight some of the same weed battles of other orchard crops and will benefit from Chateau’s long-lasting residual weed control. These registrations will not be official until EPA and state approvals, which we hope will occur in 2013.

Marrone: No, nothing recently. EPA is slow. I’ll just leave it at that. But we do hope for registration of the MBI 005 pre- and post- emergent product in April so it will be ready for some of next season. That’s my next frontier — herbicides. We started with Regalia, a fungicide, then Grandevo, an insecticide, now it will be an herbicide.

Q: In many states, such as California, ground water contamination has become a huge issue. Are you taking those environmental concerns into account? How so?

Woodwick: Protection of our natural resources is important to the U.S. agricultural industry. Our growers depend on those resources and also are very serious about being good stewards for the greater community. How Valent can help is to develop pest control solutions that deliver solid performance with minimal impact on the surrounding environment. An example of this is Chateau, which is farm friendly and can even be used in ground water protection zones because it stays where the applicator puts it, and stops weeds without leaching or lift off concerns.

Marrone: That’s what our company is all about. For example, we’re testing atrazine in combination with one of our biologicals. Mixtures are done with chemicals, and we mix foliar chemicals like fungicides and insecticides together with biologicals, so why not chemical herbicides and biologicals? Biologicals and chemicals mix fine.

To get one new biological, it costs $3 to $5 million. It’s $250 million to do a chemical. Biopesticides are small potatoes in comparison. Most small companies have one product since they do not have the capital to do multiple products. Because of all the regulatory pressures on chemicals, we are seeing bigger companies get involved in biologicals — and we will see more.

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