Predicting 2025 problem weeds a tall order

A South Dakota State University weed management specialist says it is difficult to say which weeds the state’s farmers will have to deal with this growing season. Weed seeds have built up from wet and dry years, resulting in the possibility of an unfavorable scenario, according to Eric Jones.

“In some of these wet areas we had it drowned out, so we saw weeds that prefer these wet environments, things like smartweed or barnyard grass in these drowned out areas along with waterhemp,” Jones told the South Dakota Soybean Network. “We have this seed bank built up of weeds that like dry and like wet, and so who’s to say what 2025 is going to be like, but I think we’re going to have to really expect all the weeds.”

Jones said he expects the state’s farmers will have many different weeds to cope with.

“I don’t think it will change our weed management plans, but if you are traditionally battling waterhemp and you’re not adding any herbicides to manage grasses, that could be a problem,” he pointed out.

Farmers need to focus on controlling a broad spectrum of weeds, he added. If control is concentrated on a few weed species at the expense of neglecting others, it might mean trouble later in the season.

“When we develop these herbicide plans, I like to use these tank mixes, [because] one, we get better control even on our driver weeds for the most part,” said Jones, “but we also are controlling the other weeds that may not be at the forefront of our mind to manage, but are present at densities that warrant management.”

When considering weed management, Jones’ advice is the earlier that a farmer acts, the better the outcome on a couple of different levels.

“That early-season weed competition can affect our yield even when we have crops that are small,” he said, “so if we effectively manage those and keep our fields clean, we’re going to keep our yield potential high and the amount of weeds that survive and go on to produce seeds much lower.”

When contemplating weed management programs, Jones said it is also important that growers consider resistance issues, of which there are a growing number. Among the most common resistance issues in South Dakota, according to Jones, are the Group 2 ALS inhibiting herbicides, such as Pursuit, Scepter, Beyond, Harmony and Classic.

“Those herbicides have more widespread resistance and the weeds that are resistant to those would be kochia, waterhemp, common sunflowers, cocklebur, things like that,” said Jones. “And then glyphosate resistance is probably the big one and that’s more around kochia, waterhemp and common ragweed.”

Weeds treated with a single herbicide exclusively will build resistance to that chemistry, explained Jones.

“But when you add different herbicide groups – herbicide B with it, perhaps herbicide C, that three-way mixture using herbicide B, C for a different growing season,” said Jones, “you start managing those weeds that are resistant to herbicide A, so you keep it at a lower level, that lower frequency.”

Another way to avoid herbicide resistance, according to Jones, is to control weeds mechanically by pulling them, which he concedes is likely not practical. But he adds that it should be considered on problem weedy spots in fields. Another non-chemical method to battle weed problems is by planting soybeans with narrow row spacing.

“They’re using the crop canopy earlier because the row-spacing is narrower to shade that inner row to reduce the amount of weed germination and reduce the weed growth as well,” he said. “So, anything you can use outside of the herbicide nozzle as well is going to be a benefit to keep those weeds at bay and minimize the selection pressure on herbicide-resistant weed biotypes.”

Jones is quick to acknowledge the importance of South Dakota Soybean Checkoff funding for weed management research at SDSU.

“Oh, my goodness,” exclaimed Jones, “the South Dakota Soybean Checkoff really keeps this program afloat.”

He adds that the Checkoff helps SDSU Extension do demonstrations of products from many agrochemical companies that can be applied at varying plant stages during the growing season.

“We showcase that on field days. We also publish the weed control data and yield. So, [for] the farmers across South Dakota, it’s not a gamble for them,” he said. “If they want to use a program from X Company, they can compare it to Company A, B or Z. It provides that data for them. Checkoff dollars provide us with the resources to do that.”

There is more conversation with SDSU Extension weed specialist Eric Jones on an upcoming edition of the Soybean Pod available on most podcast platforms.