Late-Season Pigweed Scouting

Pigweed plants that escaped POST applications or emerged after can now be seen above soybean canopies. Especially important are waterhemp and Palmer amaranth, as these species pose increased economic and management concerns. Waterhemp and Palmer plants can produce upwards of one million seeds per plant in certain situations. Managing these weeds often starts with preventing introductions. Anything we can do from now through harvest to prevent seed from being deposited into the soil seed bank will pay dividends down the road. At this point there are limited control options beyond scouting and hand pulling. Just a few plants left in the field can lead to a total infestation if they produce seeds.

Viability of pigweed seed is greatly reduced after 3-5 years. Management over a couple of growing seasons can drastically reduce populations. Aside from tremendous seed production, fast growth rates, and lengthy emergence windows, what makes us most nervous about these weeds is their propensity to develop herbicide resistance. In other states, waterhemp has exhibited the ability to resist up to seven different herbicide sites of action, and Palmer amaranth up to nine. Resistance to more than one site of action within a single population is not uncommon. Metabolic herbicide resistance may increase the prevalence of populations with resistance to multiple herbicide groups. Experience would tell us it's only a matter of time until we have these types of resistance issues in Ohio. The status of herbicide resistance in Ohio waterhemp populations was covered in this article.

We have a ton of resources that can be helpful for scouting, including a pigweed ID guide, pigweed management fact sheet, and YouTube video. More helpful information on the management of pigweeds can be found on the OSU weed science website.

Late-season scouting will allow us to evaluate how well our programs worked this year and forecast issues for next year. Below are some guidelines for scouting as we approach harvest.

Source: osu.edu

Photo Credit: istock-oticki