Glyphosate-resistant Palmer amaranth on turnrows and ditchbanks

Most growers in areas severely affected by glyphosate-resistant weeds realize the severity of the problem and that glyphosate-resistant weeds will be present for the foreseeable future. Control measures such as hand-weeding, which seemed extreme a few years ago, are now routinely utilized to manage glyphosate-resistant Palmer amaranth.

Growers are also becoming more educated on the importance of soil seedbanks and how these impact their weed management programs.

One area of concern in glyphosate-resistant Palmer amaranth management is controlling this species on turnrows, field borders, and ditchbanks. Clean crop fields surrounded on turnrows and/or ditchbanks by glyphosate-resistant Palmer amaranth are common sights in areas where it is prevalent.

Glyphosate-resistant Palmer amaranth has also colonized fallow areas, road sides, and construction sites. When glyphosate-resistant Palmer amaranth in these areas is left uncontrolled, it produces seed which is often disseminated into adjacent fields.

Seed industry’s future tied to herbicide resistance

Control of resistant pigweed comes at a price

NRCS offers financial assistance for resistant weeds

Managing glyphosate-resistant Palmer amaranth on turnrows and ditchbanks can be problematic. Often glyphosate-resistant Palmer amaranth in these areas is not dealt with until mid- to late-summer after weed control in the crop has concluded. However, by this time, the weeds are often large and difficult to control.

The best way to avoid problems along turnrows and ditchbanks is to never let them get “grown up.” Small weeds on turnrows and ditchbanks are much easier to control than large ones. Unfortunately, few operations can afford to have people and equipment dedicated to managing turnrows and ditchbanks, so these areas are often low on the priority list.

Some options are available to manage glyphosate-resistant Palmer amaranth along turnrows and ditchbanks. Unfortunately, none of these are foolproof. Turnrows and ditchbanks may be mowed or tilled to control glyphosate-resistant Palmer amaranth. While these tactics are relatively effective, they must be performed repeatedly because they generally do not control all Palmer amaranth plants and those remaining will produce seed which can re-infest crop fields.

Tillage, usually in the form of disking, is more effective than mowing for control of glyphosate-resistant Palmer amaranth present at the time of the operation. However, disking will require multiple passes and is only effective on turnrows, and a disk is difficult to maneuver around pointed rows and power poles. A rotary mower is much easier to handle than a disk, but it will not kill glyphosate-resistant Palmer amaranth, so the turnrow and/or ditchbank must be mowed repeatedly to avoid seed production.