Environmental conditions and weed management timing

Early completion of planting, warm soils, and adequate soil moisture may provide some interesting "opportunities" for weed management. Most crops were planted within a relatively short period of time, crop and weed emergence was quick, and growth has been rapid. Soil-applied herbicide performance has been variable depending upon post-application rainfall. Thus, the focus has turned to postemergence weed management.

Postemergence herbicide applications are timed by specifications listed on the herbicide label such as weed size or crop size, or by some "rule of thumb." Often growers delay a postemergence application, particularly for a herbicide that does not have residual weed control, until more weeds have emerged. By delaying application, better weed control will result or it may eliminate the need for additional application trips. The concern with delayed herbicide applications is that they may result in significant loss of crop yield attributable to weed interference or competition, which is of particular importance this year due to the rapid growth of weeds and limited rain across much of the state.

Postemergence weed management strategies must be timed primarily by the size of weeds and crops and the relative population of the weeds. The faster that weeds grow, and the higher the weed population, the sooner that interference and yield loss occur. Generally, due to current environmental conditions, postemergence weed management strategies should be timed sooner than in past growing seasons. Furthermore, there is a good chance that follow-up strategies may be needed to protect crop yields in 1998. Watch the weeds and crops--not the calendar--when timing postemergence weed management strategies.

This article originally appeared on pages 88-89 of the IC-480(11) -- May 25, 1998 issue.

Updated 05/24/1998 - 1:00pm