Palmer amaranth (commonly known as pigweed) is an aggressive weed that is resistant to glyphosate, can grow up to 1 inch a day, and produces a half a million seeds per plant. Because of that, it can spread quickly in fields and hedgerows, outcompeting field crops.
Even if you don’t have much land, it’s important to be able to identify and control this plant because it can spread so quickly. Palmer amaranth is on the noxious weed list in Delaware and Pennsylvania, and action is being considered in Maryland.
Palmer amaranth can look like other weeds, so here’s the low-down on identification:
• no hair on the stem, petiole or leaves, but you may see a leaf-tip hair
• seedling leaves are egg-shaped, with widest portion near the petiole
• may see a purple or white chevron marking on the leaves
• very long petioles (the leaf stem is longer than the leaf itself)
• whorled, poinsettia-like appearance in seedlings
Management of Palmer amaranth should focus on preventing seeds from developing. This means controlling plants by the time the seed heads are fully visible. Seeds are viable within a few weeks of seed heads emerging. Control measures include hand-pulling small patches in yards or around chicken houses. When hand pulling these plants, remove and dispose of the plants to prevent them from re-rooting and prevent the seeds from entering the soil.
In fields where Palmer amaranth is present, Mark VanGessel of the University of Delaware recommends you “start clean.” Use an effective residual herbicide and do not rely on applications made more than 10 days before planting. Where Palmer amaranth seedlings have emerged, treat before they are three inches tall with a product listed in the Delaware Fact Sheet on Palmer amaranth.