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By the time spring is in the air, a weed management plan should be decided and ready to put into action. However, issues that arise throughout the growing season may require some tweaks and a new plan for the next growing season. Mark Loux, a weed scientist at The Ohio State University, offers advice on managing the weed situation on any farm.

It Starts in the Fall

Fall is a good time to scout new fields or ones that have not been looked at in a while. Taking notice of what has emerged and any large areas of vegetation or tough weeds is an important step to making sure the selected program is going to work. Weeds to look for in the fall are marestail, thistle, poison hemlock and wild carrot which are harder to control going into spring and will provide an idea of which fields to treat with a fall burndown.

“Especially in soybeans, we’ve moved to trying to get herbicides on in mid to late fall. That’s the first step, and about 30% of a good marestail program. It opens the door to have an easier program in the spring,” said Loux.

Comprehensive Programs

Any no-till soybean field needs a burn down with several different herbicide sights of action and a broad spectrum residual. Some of them need fall applications and weeds that are coming back post emergence will determine the best post treatment to be used.

“Over 80 percent of our soybean acres are getting a residual pre-emergence herbicide. With more than 90 percent of beans being no-till, a fall application is a good step and everything you do needs to have diversity. It’s not just glyphosate, it needs to be a combination and the spring burndown needs to be diverse too,” said Loux.

“We’ve learned the hard way, the whole country has, that if you over simplify your approach to weed management you create an opportunity for certain weeds to establish and become really problematic. The weeds we’re battling – palmer amaranth, water hemp, giant ragweed and marestail – have a more complex biology in addition to the herbicide resistance so an approach that’s less than comprehensive won’t work,” said Loux.

It is also important to be adaptable; getting across the fields at the right time can be challenging. The plan that is in place should be adaptable on the follow through as delays in application may lead to larger more developed weeds than the program can handle.

Controlling the Seeds

New weeds don’t just come out of nowhere, they must be introduced. This can happen in a number of ways including harvesting equipment. If a specific field has a significant weed problem it should be harvested last and extra care taken to clean combines and trucks used to haul the grain.

Weeds such as palmer amaranth have also been brought in with cover crops because they are not considered a noxious weed in areas where cover crop seeds are produced. Some seed lots have become contaminated so the Ohio Department of Agriculture is providing free seed screenings to look for palmer amaranth.

“The other major source – we have at least one area that started this way – is the animal agriculture industry. Some byproducts from the south that are used for feed have been contaminated with palmer. It’s been trucked up here and used in dairies which provides two ways for transfer: the manure from the dairy and also the outfit that was trucking it – once they unloaded, they had some stuff left in their truck and they were dumping that in the corner of fields,” said Loux.

Weeds to Watch:  Marestail & Giant Ragweed

Marestail has become a major resistance problem in Ohio that needs to be taken care of with a burndown and a residual as it is very difficult to deal with post emergence. New soybean varieties, such as Liberty Link, are also a good fit for marestail and giant ragweed control.

“Another strategy is to do a really good job with a weed management program in corn and follow that up with Liberty Link beans,” said Loux. “Some of the other weeds get more complex, like giant ragweed. We have populations that are resistant to a couple different types of herbicide so it requires a pretty comprehensive approach. That may mean modifying a post emergence application to make sure you’re getting control.”

Weeds to Watch:  Palmer Ameranth

“Palmer amaranth has gotten started in about ten sites we’ve identified in the state, so we’re still in pretty good shape. The number one thing is it has to be kept from going to seed. We have a tendency to see a new weed and think it’s only a patch, I’ll take care of it next year,” said Loux. “Palmer amaranth has more capacity to overtake a field faster than any other weed we’ve ever dealt with. We’re really trying to encourage people when they see it in mid to late summer to pull it out before it produces seed.”

To get rid of palmer amaranth, it has to be pulled or dug up and taken out of the field, most of the time it is burnt after that. If left in the field it will re-root, even if the root is cut off. While there are some herbicides that can help with control it has largely doubled the cost of herbicide programs in the south. There is new technology coming that may help ease, but will not cure, the problem. It requires a very comprehensive program. To be controlled effectively post emergence it has to be less than three inches tall. Since it emerges all year and can grow over an inch a day with the right conditions, it becomes very problematic.

“We are still largely in a preventative mode, I know of one area in the state where it’s starting to move out a little bit, the rest are usually individual fields or a field with a few plants,” said Loux

New Traits and Stewardship

Over the next four to five years a lot of new technology is set to hit the market providing more options for weed management and controlling resistant weeds. Along with new technology comes the responsibility to manage it correctly.

“We’re a little bit concerned about how some of these new technologies are going to be used to make sure we don’t develop more resistance. Our fear is that people will go backwards and over-simplify their programs again. Some of that will happen, but hopefully we learned well enough and will use those in the right system,” said Loux.

“I think the key thing will be trying to think about how do we manage those appropriately and have the right stewardship,” said Loux. “The other thing is you have to make sure you’re in the right field with the right herbicide. When you have Roundup Ready, Liberty Link,  and other varieties resistant to 2,4-D and Dicamba, you start to have a situation with more potential to pull into the wrong field with the wrong mix and kill a lot of soybeans.”

There is also talk of stacked traits within the same soybean to help overcome some of those issues, but all of these new developments put more responsibility on everyone involved in the industry.

“It puts responsibility on the companies to have programs in place to help people prevent resistance, growers and applicators as well; and I think it puts responsibility back on the university to fill in the gaps,” said Loux.

For More Information Visit: http://agcrops.osu.edu/specialists/weeds