Be Prepared to Evaluate Weed Programs

Choose Preemergence Herbicides Carefully for Late Application

Pamela Smith
By  Pamela Smith , Crops Technology Editor
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DECATUR, Ill. (DTN) -- Weather events have rearranged many field operations this spring. Farmers who raced to plant before spraying weeds need to carefully weigh the subsequent use of certain preemergence herbicides.

Labels of many single and multiple active-ingredient products allow application before and after crop emergence, but not all. Some active ingredients can cause severe crop injury if crops are emerging when sprayed, said Aaron Hager, University of Illinois weed scientist.

Several scenarios have shaped up this year to warrant the warning. Warm soil temperatures can result in faster-than-anticipated germination and emergence. "Or maybe you had every intention of getting back in following planting and rain kept that from happening," Hager told DTN.

"Regardless of the reason for the delay, know what is in the active ingredient you intend to use. If there has been several days elapse between when you plant and when you spray, it is really in your best interest to scout and make sure no crop is popping through.

"Your objective is to kill the weeds. Your objective is not to kill your newly emerging crop," Hager added.

He also stressed the importance of alerting custom applicators to the fact fields are planted and when.

The extent of the injury can vary. "It's going to depend on what is out of the ground, the product being used and the coverage," Hager noted. "For example, if it is a contact herbicide, the result may be cosmetic. But if you are putting on a high enough gallonage that you are covering every bit of an exposed soybean seedling, it could kill the plant," he said.

Hager emphasized that soil-residual herbicides are important components of integrated weed management programs. Soybeans have more product restrictions than corn when it comes to using a preemergence herbicide as a post product.

"That doesn't mean you might not see some foliar injury with some of these corn products. On some of these rapidly emerging plants, the leaf cuticle may not be very thick. That's the primary barrier to uptake of foliar herbicides. If it is thin, it is going to enter the plant more quickly," he said.

In fields where a preemergence herbicide application has been delayed AND corn or soybean are beginning to emerge, Hager said the following active ingredients (applied either alone or as a premix product) or commercial products should not be applied:


-- saflufenacil (Sharpen and Verdict, for example)

-- simazine (Princep, for example)

-- flumioxazin (Fierce, for example)

-- Prequel (isoxaflutole + rimsulfuron)


-- sulfentrazone (many Authority-based products, for example)

-- flumioxazin (many Valor-based products, for example)

-- metribuzin (TriCor, a component of Boundary, for example)

-- pendimethalin (Prowl H2O, for example)

-- saflufenacil (Sharpen, Zidua Pro, for example)

-- linuron (Lorox, for example)

-- tribenuron (Canopy EX, for example)

-- clomazone (Command, for example)

Access Aaron Hager's paper on this topic:….

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Pamela Smith

Pamela Smith
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