By DOUG GRAVES

Ohio Correspondent

COLUMBUS, Ohio — Image a weed so troublesome that has mutated to resist multiple herbicides. Palmer amaranth, a member of the pigweed family, is spreading across states and growing in strength.

 “If farmers and weed scientists cannot find a new solution, crop yields could decline substantially, according to an article in Chemical and Engineering News (CEN), the weekly news magazine of the American Chemical Society.

 “Scientists are calling Palmer amaranth a ‘game changer’ because of its ability to quickly develop resistance to herbicides, including the mainstay, glyphosate,” said Melody Bomgardner, CEN senior business editor. Unlike other weeds that have developed resistance, amaranth does not pay a ‘fitness penalty’ for the adaption but instead thrives and produces new generations of resistant plants. “A single female Palmer amaranth can make up to one million seeds. The weed out competes crops for sun, water and nutrients, with the potential to drastically reduce yield for crops such as corn and soybeans.”

 Statistics from the United States Department of Agriculture, Palmer amaranth is on the rise in the Midwest. The pesky plant made its way into Indiana in 2011, spreading to Illinois, Michigan and Ohio in 2012.

 “Prior to 2015, there were only a couple of outbreaks of Palmer amaranth in Ohio,” said Dr. Mark Loux, Ohio State University horticulture and crop scientist. “Palmer amaranth was first found in Pennsylvania in 2013 and has quickly spread. The super weed has been found in alfalfa, corn and soybean fields in both states.”

 Loux says the pesky weed has made its way into 11 Ohio counties. According to Penn State Extension, between 12 and 15 sites were found in Lancaster County alone by the end of 2015.

 Wisconsin became affected, followed by South Dakota in 2014. In 2018, Palmer amaranth was discovered in North Dakota and Wyoming. Now, only nine of the 40 continental U.S. states remain unaffected by this prolific weed.

 “Because the weed is so versatile and spreads so rapidly, scientists are working to discover solutions fast,” Bomgardner said. “They want to identify the genes or mechanisms that cause resistance, which could lead to more specific recommendations for herbicides. Unlike most weeks, Palmer amaranth is dioecious, with both male and female plants. Experts could someday introduce modified weeds with pollen that produces only male plants, which could eventually cause the population to crash. For now, farmers are encouraged to use a combination of pre- and post-emergent herbicides, as well as alternative strategies, such as planting winter cover crops and implementing crop rotation approaches.”

 The weed has been detrimental to southern states as well. According to Extension specialists in Georgia and Arkansas, Palmer amaranth has invaded more than 750,000 acres of cotton and other row crops in Arkansas and more than one million acres in Georgia. It has reduced yields by up to 75 percent in some fields where it has been found.

 So what’s farmer to do? For starters, Loux and others advice planting a cereal rye cover crop. The rye can provide a mulch that will suppress Palmer amaranth emergence. Farmers are encouraged to hire hand weeding crews to remove the weed, noting that it’s important that it should be pulled and taken out of the field and composted or burned as plants that are laid on the soil in the field will re-root and continue to grow and produce viable seed.

 Other ways to rid the field of Palmer amaranth include using a deep tillage including the moldboard plow. By using deep tillage, the Palmer amaranth seed will fall below its preferred emergence depth.

 Producers are also reminded to check ditches and field borders. The fear is the weed can spread into a field through pollen and seed.

 Experts who deal with this weed say that now is the time to combat it, even through harvest.  

“Preventing new infestations of Palmer amaranth should be of high priority for Ohio growers,” Loux said. “Palmer amaranth can take over a field faster than any other annual weed. Taking the time to find and remove any Palmer amaranth plants from fields in late-season before they produce seed will go a long way toward maintaining the profitability of Ohio farm operations. The dead giveaway for Palmer amaranth as we move into late summer is the long seedhead, and those on the female seed-bearing plants are extremely rough to the touch.”

 Loux offers four tips in dealing with the weed at this time of year. First, he advises taking some time to scout fields, even if from the road or field edge with a pair of binoculars.

 “This would be a good time to have a friend with a drone that provides a real-time video,” Loux said.

“Scouting from the road is applicable mostly to soybean fields, since corn will often hide weed infestations.”

 Next walk into the field to check any weeds that could be Palmer amaranth or are otherwise mysterious. Send photos of the plant to someone who can help identify them if need be.

 Third, where Palmer amaranth is confirmed, check to see whether the plants have mature seed by shaking parts of the seedhead into your hand or other surface that will provide contrast. Mature seed will be small and very dark. Plants without mature seed should be cut off just below the soil surface.

 Finally, he says, if the Palmer amaranth population is too dense to remove from the field, harvesting through patches or infested fields will result in further spread throughout the field. If this is the case it is recommended to not harvest areas of the field infested with Palmer amaranth or harvest the infested fields after all other fields have been harvested, and cleaning the combine thoroughly before further use.

 For more information about how to tackle Palmer amaranth or other pesky weeds go to www.u.osu.edu/osuweeds

PALMER AMARANTH is easily spotted in most any soybean field, but among corn the plant often goes undetected.

(Courtesy Ohio State Univ.)