Soybean planting will be in full force shortly. No-tillers will want to pay careful attention to burndown herbicide applications due to their importance in protecting soybean yield, says a Michigan State crops and soils agronomist.
"The tendency for a number of growers, particularly those planting Roundup Ready soybeans, will be to plant into a weedy mess and not worry about applying their burndown herbicide until later," Christy Sprague says. "Or they may wait until most of the summer annual weeds have emerged before making their first post-emergence glyphosate application.
"Delayed burndown applications can reduce soybean yield, by inhibiting soybean emergence and growth. Also, by delaying applications, weeds become larger and can often times can be tougher to control. Many times, dense weed populations can even interfere with planting."
One way to give the soybean crop an early advantage is to make burndown herbicide applications before or near the time of planting, Sprague says. In Michigan State trials, she says pre-plant burndown applications of glyphosate plus 2,4-D ester made at least 7 days prior to planting, provided excellent control of most weeds present prior to planting.
Burndown applications of glyphosate that were delayed until soybeans were at the VC (unifoliate) to V1 (1 trifoliate) growth stages resulted in an average yield loss of 8.3 bushels per acre, Sprague says. Waiting until soybeans were at the V3 growth stages resulted in a 9.2-bushel-per-acre loss.
In addition to protecting yield by reducing early season weed competition, Sprague says starting the growing season with a clean field will also eliminate several winter annual weeds that may potentially serve as hosts for destructive insects and soybean cyst nematode.
"If a burndown herbicide application cannot be made prior to planting, it should be made shortly thereafter," Sprague says. "Any delays in these applications can reduce soybean yield."
Sprague cautions no-tillers that treatments containing 1 pint per acre of 2,4-D ester need to be applied a minimum of 7 days before soybean planting.