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Timing Of Early Preplant Herbicides

Timing Of Early Preplant Herbicides

With a cold, wet April the opportunity to apply early preplant herbicides for corn can best be summed up as "opportunity lost." So what should you do now? Do not wait to apply a residual herbicide for your corn crop postemergence with a burndown herbicide such as glyphosate or glufosinate, says ISU's Mike Owen.

As the calendar flips from April into May 2011, weed growth is well underway in Iowa fields. It's another crop yield destroying opportunity for weeds.

"Unless you were able to take advantage of the one or two days available for fieldwork in April, the opportunity to use a soil-applied residual herbicide for weed management in corn in the manner that provides the most stewardship and economic benefits has been lost this year," observes Mike Owen, Iowa State University Extension weed management specialist.

He adds, "Now is the time to consider the next best opportunity to protect crop yields as well as to provide the necessary stewardship to mitigate the evolution of herbicide resistance in weeds for fields that are to be planted to corn this spring." Owen offers the following "do's and don'ts" regarding weed control, considering this spring's delayed corn planting.

Advises against waiting to apply herbicides until later for corn

DO NOT wait to apply the residual herbicide products for your corn crop postemergence with a burndown herbicide such as glyphosate or glufosinate. Doing so will guarantee considerable loss of crop yield potential and thus profit. Given the high corn prices the market is now offering, this could be costly indeed.

The next best decision in these delayed corn planting situations is to apply the residual corn herbicides in combination with a burndown product immediately prior to, or immediately following planting. But be sure to do it prior to the emergence of the crop, says Owen.

EPP herbicide opportunities still exist for soybeans but again, given the weed growth that currently exists, a burndown product must be included with the soil-applied residual herbicide. The sooner you are able to apply the soybean herbicide, the better the weed management and the greater the soybean profits.

Keep weed resistance in mind when selecting herbicide products

Selection of soil-applied herbicides must be done with an understanding about the existing resistances to herbicides in weeds and your selection must also reflect the herbicide mode of action of the products selected, says Owen. Pay particular attention to controlling waterhemp.

Keep in mind that all waterhemp in Iowa fields should be considered resistant to ALS inhibitor (Group 2) herbicides. Thus, any herbicide (single product or pre-package mixture) that is a Group 2 product will not provide any management or stewardship with regard to waterhemp, advises Owen.

"In Iowa, we now have resistance to ALS herbicide products, HPPD products, triazines, PPO products and glyphosate products in waterhemp populations," he points out. "And in most instances, the waterhemp populations have multiple herbicide resistances. The take-home message is to make your selection of herbicides a well-thought out and informed decision."
TAGS: USDA Extension
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