Depending on where you farm, Palmer amaranth and waterhemp can be 2 notorious pigweeds that give you a hard time, season after season.

The Ohio State University Extension’s Agronomic Crops Network says both weeds can develop resistance to new sites of action (SOAs) used in post-emergent herbicide treatments within 3 cycles of use. Prolonging resistance development requires constantly changing herbicide strategies.

The time and effort you put in this season can have far-reaching implications for next year. Protect 2020 yields by scouting fields in late summer this season. Do this by removing and destroying weeds before they go to seed.

Both weeds look similar, making it challenging to tell them apart at various growth stages. For information to help identify Palmer amaranth and waterhemp, read our previous posts in the Weeds Waking Up series.

The key visual difference between Palmer amaranth and waterhemp is the long seedhead that Palmer amaranth develops in late summer. To determine whether the weeds have mature seed, crush the seedhead in your hand or against a hard surface, such as pavement. Both Palmer amaranth and waterhemp produce small, dark seeds at maturity.

If you find pigweed plants with mature seed, be sure to dispose of them using methods that prevent the seeds from dispersing in the field, such as cutting them off and bagging them.

Scouting and cleaning fields now can also prevent weeds from interfering with your harvest. Combines can become contaminated with pigweed seeds if Palmer amaranth and waterhemp plants are mixed in with the crop. Those seeds can be accidentally spread around farms by using the same combine on other fields.

According to the University of Arkansas Division of Agriculture Research & Extension, contaminated equipment that is rented or sold can transfer weed seeds over large distances, even across state lines. If seeds from herbicide-resistant weed populations are hiding in that equipment, resistance can spread to new places where those SOAs had still been effective.

It’s crucial to thoroughly clean combines and other machinery after operating in an area of high weed pressure. Affected fields may need to be harvested last to prevent cross-contamination.

Late-season pigweed pressure poses significant challenges, not only for this year, but also for the next. That’s why we recommend using an effective herbicide program to manage tough weeds throughout each growing season.

For your soybeans, we recommend a preemergence application of Boundary^® 6.5 EC or BroadAxe^® XC herbicide, both of which can be followed early post-emergence by Tavium^® Plus VaporGrip^® Technology herbicide, the market’s first premix residual dicamba herbicide approved for use on dicamba-tolerant soybeans. Tavium is a formulation of dicamba and S-metolachlor, making it a convenient application for growers looking for strong contact and residual control of tough weeds.

For corn, we recommend Acuron^® corn herbicide and its atrazine-free counterpart, Acuron Flexi. Acuron outyields the competition, because it kills weeds that competitor products miss. Both Acuron and Acuron Flexi can be followed by Halex^® GT corn herbicide, plus either an atrazine or dicamba herbicide for season-long control of annual grass and broadleaf weeds.

Don’t let this year’s weeds reduce next year’s yields. Scout now and remove tough weeds before they go to seed.

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