Hard-to-Control Weed Creeps into Eastern Corn Belt
Published: Friday, December 20, 2019
Water hemp is here in the Midwest, adding to the woes of Indiana farmers. Bill Johnson, Purdue University weed expert, said, "It is here in almost every county in Indiana even though it may not be a problem for every farmer—yet."
Johnson explained, "It has been prolific in Missouri, southern Iowa and eastern Kansas and has slowly migrated its way to our geographic area."
Like other weeds, it is transported by waterfowl, through poultry litter used as fertilizer, and contaminated farm machinery.
"Farming practices used to rely on simple tactics," Johnson said. "Now, more farmers are farming more acres and moving machinery over greater distances and taking these seeds with them. Water hemp adapts very easily."
Although water hemp is in the pigweed family, it is much harder to control than redroot pigweed, the variety that most people picture when they think of the species.
One of the reasons why water hemp is so hard to control is because of its germination and emergence characteristics. Unlike most summer annual weed species that emerge primarily during the early part of the growing season, water hemp emergence can easily occur during the middle to late part of the growing season.
It is common practice, especially in no-till, to apply herbicide several weeks before planting to receive sufficient precipitation to incorporate the herbicide. The current soil-applied herbicides may not have sufficient soil-residual activity to control late emergence flushes of the water hemp.
On the flip side, certain post-emergence herbicides can control water hemp present at the time of application but may not provide sufficient residual control of plants that emerge after application.
On top of its difficulty to control, water hemp gets its competitive edge because it can grow faster than most crops or weeds. Johnson said, "It can easily grow one to one and a half inches per day and the taller the plant, the more sunlight it can capture."
So, how are Hoosier farmers supposed to combat this new weed threat? Johnson recommends, "Full speed ahead with herbicides. We see it all the time, when soy bean prices are low, farmers want to cut costs and one of the first ways that they do this is to cut back on their herbicide rates. This won't work when dealing with water hemp because, besides being prolific growers, they have a remarkable ability to adapt. Even a few escaped plants can mean disaster in coming years. Be good stewards of the land and use full strength applications."
Johnson also stressed consulting the fact sheets. Purdue University, the University of Missouri, University of Illinois, all the chemical companies and other sites have guide sheets explaining what herbicides work best with water hemp and list full rate herbicide information.
John Alyea, a farmer in Wayne County, Ind. is a little concerned. He hasn't seen any water hemp on his farm yet, although Randolph County to the north of him has been fighting it for the last several years.
"I was spraying last year and got rained out. Later in the season I finished spraying but noticed at harvest some pigweed coming up in the beans. I am concerned what next year will bring, I definitely want to keep ahead of this," he said.
Dan Hemker, whose acreage is in southern Michigan, is also concerned.
"I don't have any yet and I haven't heard of any up this way, but I know it's only a matter of time. This is everyone's problem."
Water hemp requires an integrated weed management system. Time of application and rate of application are crucial. Johnson stressed how important it is to control water hemp in relation to yields.
"Corn yields are not affected as much as soybeans because corn can tolerate more diverse chemical applications. Depending on infestation, water hemp presence can decrease soybean yields up to 30 percent. That's major and why we need to get a handle on this menace."
It's a double-edged sword for farmers. As prices go down, they tend to spend less on herbicides which gives weeds like water hemp the advantage. If they do spend more on herbicides, it may still be in vain unless they time their application just right. No one ever said farming was easier, and it just got a little harder.
Return to Top of Page