What is in this article?:
- Kentucky researchers tackle herbicide resistant weeds
- Fulton County problems
- Union County trials
Palmer amaranth and waterhemp share many similarities. They are in the pigweed family, are similar in appearance, produce male and female plants that must cross to reproduce and are problems in soybeans. Although both species have been in Kentucky for more than 10 years, problems controlling them with glyphosate did not appear until the past few years.
Fulton County problems
The ground in Fulton County with the greatest concentration of Palmer amaranth is in the Mississippi River bottom lands. It is not conducive to traditional Kentucky crop rotation, because annual floods from the river cover the ground well into the spring. Only soybeans have been successfully raised on this ground, said Cam Kenimer, Fulton County Extension agent for agriculture and natural resources.
Palmer amaranth can grow 6- to 7-feet tall, and each plant produces thousands of seeds. The weed takes moisture away from the crop, which can reduce yields, Kenimer said.
Barrett began a weed management trial for Palmer amaranth at Jim Major's farm along the Mississippi River bottoms in Fulton County this year.
"We've had Palmer amaranth on a limited basis for the last three or four years, but last year, it mushroomed out of proportion," Major said. "It's spreading out more to upland ground."
To minimize the spread of Palmer amaranth, growers need to control the weed before it goes to seed.
"We are still gathering information, but we should have specific recommendations shortly," Barrett said. "It appears it's going to be a combination of a soil-applied herbicide and a post-emergence herbicide. These two things should reduce the likelihood that the plant develops resistance to one of the treatments. We are considering adding information on both Palmer amaranth and waterhemp into the 2011 edition of AGR-6, Weed Control Recommendations for Kentucky Grain Crops."
Waterhemp is a common weed in the Midwest and has been in Kentucky for many years. But glyphosate-resistant plants only started showing up in the past few years. Glyphosate-resistant waterhemp is found in western Kentucky from Hancock County to Fulton County, but is most prolific along the Green and Ohio rivers. Like Palmer amaranth, glyphosate-resistant varieties may have entered the state on field equipment. In Illinois, weed specialists have found some waterhemp plants that are resistant to several different herbicide classes.
Waterhemp can be anywhere from 4- to 12-feet tall and produces thousands of seeds.
"It's a weed that can get out of hand really quickly because of the number of seeds it produces," said William Witt, UK weed scientist.