Timely postemergence herbicide applications in soybean can increase profits
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EmailEditor’s note: This article is from the archives of the MSU Crop Advisory Team
Alerts. Check the label of any pesticide referenced to ensure your use is
included.
Early
season weed competition may be one of the biggest contributors to unseen
yield losses in soybean. Appropriately timing postemergence herbicide
applications is critical to preserving crop yields. Several studies have
shown that delaying postemergence weed control strategies can
substantially reduce crop yield. This has become more of a concern with
the large number of glyphosate-resistant crop acres that rely on
postemergence applications of glyphosate for weed control. We are not
saying that postemergence herbicide application timings are not
important in non-glyphosate-resistant crops, but herbicides generally
used in these crops are most effective on small weeds. Therefore,
growers that are growing non-glyphosate-resistant crops are probably
already making postemergence herbicide applications early. If they are
not, it is important to also follow the outlined guidelines for
postemergence herbicide applications.
In glyphosate-resistant soybeans, there is the temptation to delay
postemergence glyphosate applications until all of the weeds have
emerged. Delaying these applications can rob soybeans of this maximum
yield potential. As mentioned before, research throughout the Midwest
and Canada has shown the importance of early season weed control. For
example, research conducted in Ontario has shown that delaying herbicide
applications more than four weeks after soybean emergence can reduce
yield about 0.75 bushel/acre/day.
Over a four-year period, MSU conducted research to study the effect of
glyphosate application timing and row spacing on corn and soybean yield
loss from weed competition. This research showed that in at least one of
the years that this research was conducted, if weeds were allowed to
reach 6-inches in height before control, yield was reduced in narrow row
soybeans and 30-inch row corn. Depending on when this yield loss
occurred, soybean yield was reduced from 2.5 to 5.5 bushel/acre/day.
This starts to add up when you consider the economics. Considering these
crop loss estimates, delaying herbicide applications three days would
cost you any where from $56.25 to $123.75/acre in soybeans ($7.50 new
crop soybean.) Waiting to make postemergence herbicide applications can
cost you money. Therefore, it is important to follow the recommendations
to avoid yield losses due to early season weed competition.
Recommendations
Weeds should be controlled in:
- 7.5 and 15-inch row soybean before weeds exceed 4-inches.
- 30-inch row soybean before weeds exceed 6-inches.
