Can you ever imagine a situation where you would be happy to find a weed seedling emerging in your field? Normally a weed is public enemy number one.
Weeds still are enemies, but imagine your relief if you find a weed seedling early after planting that escaped residual control, and looks like it might be waterhemp or Palmer amaranth, but turns out not to be either one. Instead, it's just plain old redroot pigweed, a weed you know how to take out.
Deciding the seedling is redroot pigweed, and not Palmer or waterhemp, might be cause for celebration!
Bill Johnson, Purdue University Extension weed control specialist, says there are ways to distinguish common redroot pigweed from its more difficult-to-control cousins. For one thing, young redroot pigweeds don't form a rosette shape of growth when viewed from above. Palmer amaranth plants do. Waterhemp doesn't either, however.
Redroot pigweed leaves will be somewhat more ovate or round in shape, more like Palmer amaranth leaves. The difference is that Palmer leaves have a longer petiole, or extension from the stem to the leaf. It's distinctly longer than those of either pigweed or waterhemp.
One of the best ways to tell these hombres apart is whether or not they have hair on their leaves and stems. As you look at the tiny pigweed you've found in your field, you're hoping that there is hair developing on the stems and leaf surfaces. Only redroot and smooth pigweed have hairs. That would eliminate both Palmer amaranth and waterhemp. Neither of them have hairs on their leaves or stems. So if you have hair, you can believe a sigh of relief.
Here's a note about identifying these tough species. There are variations amongst individual plants within a species. Some may look slightly different in leaf shape. However, lack of hair on Palmer and waterhemp is a consistent trait.