Resistance puts on the pressure

Published on: 09:00AM Jun 19, 2009
In northeast Arkansas, near where the state’s first confirmed case of glyphosate-resistant Palmer pigweed appeared, this competitive weed is putting the pressure on soybean and cotton growers.

According to one of my colleagues in the field, the first photo shows “average” Palmer pigweed pressure before planting soybeans. Wet weather has pushed planting late, but growers are getting a good look at their weed pressure. This field will be burned down with glyphosate and a residual, because although these plants may not all be glyphosate resistant, growers don’t want to select for resistance.

The second picture shows how an effective application of glyphosate and a pre-emergence herbicide can allow soybeans to emerge. Note the number of weed carcasses – without a good burndown, the soybeans don’t have a chance.
This heavy pigweed pressure has become more noticeable in the last couple years, as resistance has spread. In the past, Palmer pigweed wasn’t a key weed concern in this area.  Glyphosate could kill large weeds. But growers are learning now that timing is critical.  For best results weeds should not be allowed to emerge, and Palmer is one weed I want to control before it emerges.  That takes planning and the use of a preemerge residual herbicide.   You have a management plan laying out what crop you are going to plant in each field, the fertilizer you plan to use…we just need to do the same for weed control to stay ahead of the problem.