By Mike Owen, Department of Agronomy
I spent an enjoyable Wednesday driving around central, southeast and east central Iowa looking at some on-farm demonstrations we have established. It was wet and muddy to be sure and there is no question that herbicide applications have been delayed by the weather.
The consistent observation I made was that the soybean crop is going to be less than it could have been if growers had practiced weed management earlier in the season. We still may have a good "weed killing" opportunity, but untold bushels of soybeans have been lost due to weed competition.
Most of this yield loss could have been avoided if an early preplant herbicide application had been used in early April. The pictures below illustrate the problem and the solution.
Note the weedy foreground of the picture and the clean field where a soil-applied residual herbicide had been applied.
This weedy field may be controlled eventually, but to what end? The 2009 soybean yield potential has already been dramatically reduced regardless of how dead those weed eventually become.
My advice is to look closely at the fields now, determine which weeds are most problematic in the fields and devise a management plan to be initiated early next growing season. The 2010 yield you protect will more than pay for the cost of the residual herbicide treatment.
Note: This article is a blog entry on the CropWatch Blog; this and the entries of Iowa State University Extension field agronomists discuss Iowa weed issues.
Micheal Owen is a professor of agronomy and weed science extension specialist with responsibilities in weed management and herbicide use. Owen can be reached by email at email@example.com or by phone at (515) 294-5936.