Kurt Vollmer, Weed Management Extension Specialist | kvollmer@umd.edu
University of Maryland Extension
Trying to spray pigweeds now isn’t worth it since flowers are present, and it’s almost time to harvest. The damage to crop yields is already done, and it’s better to focus on next year. Knowing which weeds are in your field can help you make better decisions. While it’s not ideal to wait until pigweeds are this far along, their flowers can help you tell the difference between the bad ones from the really bad ones.
Since Palmer amaranth and waterhemp are noxious weeds in Maryland, it’s necessary to remove them from fields, or at least stop them from spreading. Right now, both species have long, thin flower spikes—about 2 to 3 feet for Palmer and 1 to 2 feet for waterhemp—especially in mature corn and soybean fields (Figure 1). These two species produce male and female flowers on separate plants. Male Palmer flowers feel soft while or female flowers have sharp, leaf-like parts called bracts (Figure 2). Waterhemp flower clusters are more spread apart on the spike, and their female flowers do not have sharp bracts like Palmer amaranth (Figure 3).
Smooth pigweed and redroot pigweed have much shorter flower spikes, only about 0.5 ft to 0.7 feet. These species have both male and female flowers on the same plant. Redroot pigweed flower spikes are short and stubby, while smooth pigweed flowers are a bit longer and thinner Figure 4).
Remember, different types of pigweeds may be growing in the same field. To learn more about how to tell them apart and manage them, check out Keys to Identifying Palmer Amaranth and Waterhemp.
