In recent years, glyphosate-resistant weeds common north and south of Kentucky have appeared in the state. While glyphosate-resistant marestail is widespread in Kentucky, Palmer amaranth and waterhemp are new problems in certain counties.

Weed scientists in the University of Kentucky College of Agriculture are exploring different methods of control for these weeds with the hopes of containing them to the already-infested areas.

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 growers were the first to observe control problems with Palmer amaranth. A recent survey found that glyphostate-resistant Palmer amaranth is now in all four Kentucky counties that border the Mississippi River. Native to the Southwest, Palmer amaranth has spread across the Southeast. In states to the south, it's a major problem in cotton as well as in soybeans.

"Kentucky is different from the states to our south, in that most of our grain crop acreage is rotated; so our growers have used multiple weed management practices on the fields. It's kept us from having a lot of weed problems," said Michael Barrett, UK weed scientist.