Solving Weed Problems

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 the first of our four-part series on crop protection, we talked with representatives from a couple of companies that are focusing on solving growers’ problems with weeds. One is Kelli Woodwick of Valent USA, brand manager for Chateau herbicide (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.

Q1 What are the biggest challenges vegetable growers are facing these days?

WOODWICK: These days vegetable growers in the U.S. face many challenges with regulations, including federal and state, as well as international regulations related to maximum residue levels (MRL). They tell us that in making herbicide choices they must consider compliance with many regulations as well as what crops are planted in close proximity.     

In addition to regulations, growers have shared how important it is to get weed control in both the row middles and around the perimeter of their vegetable crop. The reason this is critical is to limit the host plants for pests that may carry viruses or bacteria into the crop. Control of weeds like nightshade in tomatoes is an example of how solid weed control can help minimize the impact of tomato chlorosis virus. This is also true in potatoes, where nightshade has been found to be host for late blight, aphids, and even a host for Colorado potato beetle.

MARRONE: This is really not my area of expertise, but it would be pre-emergence products. For organic growers, there’s nothing, so they use mechanical means and flaming. But both are expensive. There is no cheap answer for organic growers. 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.

Q2 Have any weeds emerged in recent years that represent particularly thorny challenges for vegetable growers?

WOODWICK: Yes, there are different weeds — thorny and otherwise — in various vegetable growing regions. As mentioned earlier it is important to get control of nightshade to protect the yield as well as the quality of the produce. Also, for some regions acetolactate synthase inhibiting herbicide (ALS) resistant pigweed has become a challenge, and with the wide use of glyphosate many vegetable crops have challenges with glyphosate-resistant marestail (horseweed) and Italian ryegrass.

MARRONE: I do know of a few, such as little seed canary in onions. And in asparagus, common groundsel has become a problem.

Others are marestail, also called horseweed, and fleabane. As I said, growers need new products, and there will be a lot of new biological 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 the new products are broader spectrum.

Q3 Does Roundup resistance  continue to be a problem?  With what weeds?  What can growers do?

WOODWICK: Yes, glyphosate resistance is a nationwide concern in many crops. For most vegetables crops it can be managed relatively well due to the use of cultivation and alternative pre-emergent or preplant herbicides. Growers who rotate between Roundup-Ready cotton and tomatoes or other vegetable crops should be vigilant in use of alternative herbicides. Or if they are growing vegetables in and around an area that has a lot of soybeans, they should keep a watchful eye on emerging tough weeds and adopt the use of a non-glyphosate herbicide program to get control of those weeds early. 

MARRONE: Yes, the weeds I mentioned are all especially problematic because of Roundup resistance problems. For marestail, fleabane, etc. growers are desperate for new modes of action.

They have to start using different chemicals. 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.

Q4 Has your company come out with any new herbicides and/or label additions? Growers of what crops would be interested?

WOODWICK: Chateau Herbicide has proven to be a great tool to prevent nightshade, mustards, pigweed, and many other common weeds in potatoes. Growers in the Pacific Northwest have found the chemigation label useful in getting it applied on a timely basis. I am also excited to share that we received federal approval for fallowbed treatment with plantback to transplanted tomato and melons. This is a good option to get control of tough weeds before they take off. Garlic and asparagus growers also love the weed control offered by Chateau, and have used it successfully for a few years. Plus, Valent offers Select Max Herbicide with Inside Technology for post-emergent control of grasses in many vegetable crops.

MARRONE: We have one product 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, the first in 20 years. That’s my next frontier — herbicides. We started with Regalia, a fungicide, then Grandevo, an insecticide, now it will be an herbicide.

Q5 In many states, such as California, ground water contamination has become a huge issue. Some agencies are pushing for runoff from ag land to be of virtual drinking water quality. Are you taking those environmental concerns into account? How so?

WOODWICK: As you know, protection of our natural resources is important. 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 herbicide, 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, a chemical that’s always under attack. It’s more for row crops, but to mitigate the risks, we’re taking products like that and testing our products (biologicals) with them at extremely low rates. It’s a new concept — no one’s thought of that one as far as I know. It’s done with chemicals (mixing active ingredients together), and we mix chemicals and biological together with foliar products like fungicides and insecticides, so why not herbicides? Biologicals and chemicals mix fine.

In the past, biologicals were just not mixed at all with chemicals or with each other. To get one new biological it costs $3 million. It’s $250 million to do a chemical. Biopesticides are small potatoes in comparison. I have three new herbicides under development, but I was able to raise $40 million, and that’s rare for a small company to do. Because of all the regulatory pressure and increasing use of biologicals plus chemicals to increase performance and yield, we are seeing bigger companies get involved in biologicals — and we will see more.  

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