Be on the watch for ‘super pigweed’

Farmers and gardeners know that weeds will become a serious problem if left to compete with the crop. Weeds will rob the crop of nutrients and water, and may affect quality at harvest time.
Weeds that were easy to control may become a problem when farmers switch to new practices such as no-till or organic agriculture.
Even the farmer who thought that glyphosate (Roundup) would control any weed, found out that with continual use of the same herbicide and control method, selected weed populations become resistant.
The Hancock County Extension office, with assistance from Legacy Farmers’ Cooperative, does a weed survey in soybean fields shortly before harvest to determine which weeds may have adapted and survived control methods and may have become resistant to common herbicide programs.
The 2013 survey identified marestail, giant ragweed and common ragweed, in that order, as the most difficult weeds to control. However, the severity and frequency of these weeds was considerably less than 2012.
Farmers have learned from Extension programs and experience that effective marestail control requires no marestail present at planting time, residual herbicides to control emerging seedlings after planting, and other herbicides with a Roundup program.
The weed that is the biggest concern was not found during the survey. That’s good news for the region.
The weed of concern is palmer amaranth, Amaranthus palmeri, AMAPA.
Palmer amaranth is a member of the pigweed family. This pigweed has drastically changed soybean production in the southern states and other areas of the country.
Pigweeds are not new to our farmers, who have effectively controlled the common pigweeds found in fields, redroot and smooth, with herbicide programs.
Pigweeds in general are summer weeds that have oval- to diamond-shaped leaves that alternate on the stem. Plants tend to be tall and upright to bushy. Flowers are small and greenish in dense clusters in leaf axils and stem terminals.
However, palmer amaranth has been referred to as a super pigweed or a pigweed on steroids that is difficult to control. Many of its populations are resistant to common herbicides.
It grows rapidly, as much as three inches per day under ideal conditions. The weed can cause as much as 80 percent yield loss in soybeans without effective control.
Plants are male or female, almost guaranteeing the spread of new genes, which allows it to quickly adapt to new environments and spread herbicide-resistant genes.
Palmer amaranth seeds are very small and easily move as contaminants in grain, seed, or feed, and with farm machinery such as combines. Seeds need to be near the surface to germinate and establish plants, thus, no-till or minimum-tilled fields are ideal environments.
Female plants are prolific seed producers. One plant competing with soybeans can produce 100,000 seeds in a growing season and, in non-competitive situations, produce 500,000 seeds.
Palmer amaranth is native to the deserts of the southwestern United States and northern Mexico. It has established itself in the southeastern United States and has moved into Indiana and Michigan, and a few isolated areas of Ohio.
Two identification features that separate palmer amaranth from the six other pigweed species include lack of hairs on the stems, and petioles, or leaf stalks, that are as long as or longer than the leaf.
Farmers and individuals need to be vigilant not to inadvertently bring in palmer amaranth seeds in livestock feed, conservation program seed, and farm machinery purchased from areas with the weed.
Palmer amaranth has not been found in northwestern Ohio. If plants are found, they need to be removed and prevented from going to seed.
Call the Hancock County Extension office if you suspect a plant is palmer amaranth. Pigweed identification keys and other resources on palmer amaranth may be found on Ohio State University’s Agronomic Crops Team website,
Let’s keep this weed out and protect our soybean industry. We do not want this weed to appear in the next fall soybean weed survey for the county.
Lentz is extension educator for agriculture and natural resources for The Ohio State University Extension Service in Hancock County. He can be reached at 419-422-3851 or via email at
Lentz can be heard with Vaun Wickerham on weekdays at 6:35 a.m. on WFIN, at 5:43 a.m. on WKXA-FM, and at 5:28 a.m. at 106.3 The Fox.


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