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Don't Wait to Spray Soybeans in Drought

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Written Thursday, July 01, 1999  

An Ohio State weed specialist says Ohio farmers planning postemergence applications for their soybeans need to do so now.

Soybean plants may incur some herbicide injury now, but they are young enough to outgrow the injury and still produce respectable yield, says Extension Associate Jeff Stachler.

"Now's the critical time to get weed control done in soybeans in order to reduce yield loss due to weed competition and soybean injury," Stachler says. "The earlier we get it done, the better off we'll be."

Soybeans should be sprayed if they are beyond the second trifoliate growth stage, which likely is fields planted before mid-June, Stachler says. Definitely any soybeans planted in April and May should be sprayed by the Fourth of July. "I'm seeing a lot of big weeds that are appearing that need to be sprayed." he says.

Also, do not shortchange weed control by using lesser treatment rates, Stachler says. Use rates recommended on the product label, and follow all application instructions.

For the most effective weed control, farmers should use all appropriate adjuvants in their tank mixes, Stachler says. These include methylated seed oils (MSO) and crop oils that penetrate weed tissues. An MSO with an acetolactate synthase (ALS) inhibiting herbicide and Flexstar will provide enhanced weed control. Other kinds of adjuvants and surfactants, provide cover the weed leaf surface more evenly.

During hot, humid, drought conditions, the best time to spray is when temperatures are cooler during the early morning or in the evening, Stachler says. This can provide better control because biological processes of drought-stressed weeds can "shut down" in the extreme heat of the day. Weeds are physiologically more active during cooler times, which helps move herbicides throughout the plant.

Waiting until too late in the season to spray can result in weeds that are too large to control with contact herbicides, Stachler says. That's because these products only disrupt plant cells at the point of contact with the tissue, he says.

The Ohio Agricultural Statistics Service reported 10 percent of the state's soybeans were blooming as of June 27, or 8 percent ahead of the five-year average. The service rated 59 percent of soybeans in good or excellent condition, compared to 66 percent for the previous week, and 61 percent for the same time last year.


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