Volume
2 Issue
6
June 28,
2005
Rapid Corn and Soybean Growth is
matched by “Weed” growth!
Consider corn growth stages when making
postemergence
herbicide choices.
Corn and soybean growth is now
accelerating because of the recent warm and wet weather.
The Minnesota Dept of Agriculture Statistics Service
reported that as of last week the average corn height in
Minnesota was 12 inches compared with 13 inches last year
and for the five-year average. Soybeans were 91% emerged
versus 95% last year and 95%as the five-year average.
Soybean height was 4 inches compared with 5 inches last
year.
While the recent weather has been more favorable to the
growth of corn and soybeans it also has been just as
favorable to the growth of weeds. The prolonged period of
rain in May and June has prevented timely application of
postemergence herbicides in many corn fields for the
control of weeds. By the time conditions allow field work,
corn may be beyond the optimum size for postemergence
applications. There are several concerns with delayed
applications, including:
- label restrictions regarding crop or weed size,
- increased sensitivity of large corn to herbicides,
and
- reduced efficacy due to large weed size and/or
canopy interference with spray coverage.
The reference tables list the maximum corn size
specified on herbicide labels. As corn increases in size,
the crop canopy intercepts a significant portion of the
herbicide spray. This may reduce performance due to
inadequate coverage of weeds or enhance the potential for
crop injury. Drop nozzles will reduce these risks by
directing the spray to the weeds, therefore improving
coverage and reducing corn exposure.
Table 1. Grass Herbicide Restrictions for Corn
Table 2. Broadleaf Herbicide Restrictions for Corn
Table 3.
Herbicide restrictions for resistant corn hybrids
David Nicolai
U of Minnesota Regional Crops Educator, Hutchinson
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