Iowa State University

The importance of an even start   
by Bob Hartzler

December 16, 2005 - While the importance of providing the crop an even start with weeds has diminished in many farmers’ minds, this practice is still the first step in successful weed management. In no-till an even start can be provided either by applying a burndown herbicide soon before or after planting, or by applying early preplant herbicides prior to weed establishment. In systems utilizing tillage, planting soon after the final seedbed preparation tillage operation insures the crop emerges with early-season weeds rather than after.

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 can be shortened significantly if weeds are established at the time of 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 postemergence 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.

Prepared by Bob Hartzler, extension weed management specialist, Department of Agronomy, Iowa State University