Weed Escapes Could Be Problematic This Year

Syngenta agronomists discuss replant calculations for corn and soybeans.

Published on: May 12, 2014

Depending on when farmers applied a pre-emergence herbicide, escapes could be a big problem this year.

Blake Miller, a Syngenta agronomist based in Monticello, notes farmers were tempted in early April to apply their chemical package in less than optimal conditions. Miller's coverage area primarily includes western Illinois. He's concerned many put down their burndown pre-emergence herbicide before weeds were actively growing. As a result, marestail could be growing uninhibited in numerous fields.

"The primary goal should always be to start clean," Miller notes.

Once marestail pushes past three inches of growth, post-emergence control becomes a serious issue. A severe infestation in soybeans can result in 40% yield reductions.

Weed Escapes Could Be Problematic This Year
Weed Escapes Could Be Problematic This Year

For those attempting to control marestail post emergence, Miller recommends a tank mix of Halex GT plus atrazine in corn. For soybeans, he says Touchdown Total, 2,4-D and Boundary 6.5 EC followed by an in-season application of Flexstar GT 3.5 will give farmers the best shot at controlling this tough weed.

Post-emergence control
For those who struggled to get the crop in the ground, a pre-emergence herbicide was probably an afterthought.

Syngenta agronomist Todd Thumma says these folks will still want to get some sort of residual herbicide on the crop, even if it's in a post-emergence situation. He recommends Lumax EZ and Lexar EZ in corn fields.

In soybeans, marestail and giant ragweed escapes are a tougher issue. "We could make it mad, especially if it's Roundup resistant," Thumma notes. "We don't want to do that."

Thumma says a lot of these weeds become issues as farmers push herbicide applications too close to soybean planting, which forces them to remove 2,4-D from the tank mix. That's a big no, no.

In these situations, he recommends Flexstar GT 3.5 to help burn back marestail and giant ragweed escapes. Of course, it's important to get to these weeds as soon as possible.

Replant calculations
It seems any difficult planting season wraps up with the dreaded replant.

Thumma notes many folks are willing to tear up a corn field and replant if as-planted populations fall at or below 27,000 plants per acre. On soybeans, the number is around 80,000 plants per acre.

However, Thumma says most would do well to lower these thresholds a bit. On corn, he says 24,000 plants per acre is more reasonable. For soybeans, 100,000 is a good number.

"Most don't realize at 24,000 plants per acre, your corn crop can still yield in the low 200s," he adds.

Unfortunately, it will be tough for Thumma's advice to catch on any time soon. "The last few years, replant corn has been fantastic," he adds.

Still, there will be years it doesn't pay. That's why he challenges folks to consider letting it ride if it's close to these thresholds.