Providing the crop an even start with weeds is still the first step in successful weed management, although the importance of this practice has diminished in many farmers' minds. An even start is provided by planting soon after the final seedbed preparation tillage pass, or in no-till by applying a burndown herbicide soon before or after planting, or use of early preplant treatments prior to the weed establishment.
|Winter annuals such as horseweed should be controlled at planting.
Ignoring weeds present at planting provides the weeds a competitive advantage with the crop, creating a situation where weeds can impact crop yields very early in the season. Weeds that emerge after planting can begin to impact crop yields within two weeks of emergence; this time period may be shortened significantly if the weeds were established at the time of corn planting.
The practice of delayed burndown applications in no-till fields where an early postemergence application is used to control weeds present at planting carries a high risk of yield penalties due to early-season competition.
The objective of weed management is to protect crop yields rather than kill weeds. Today's post-emergence herbicides are able to control much larger weeds than was possible in the past, yet this creates the potential for hidden yield losses due to competition. Allowing weeds a head start on the crop greatly increases the likelihood of early-season yield losses. Thus, an even start for crops with weeds remains the foundation of sound weed management programs.
Weeds can begin to reduce yields shortly after crop emergence.
This article originally appeared on page 52 of the IC-494 (6) -- April 11, 2005 issue.