Recently, the weed science program at the University of Illinois published recommendations for the management of Palmer amaranth in Illinois agronomic crops. One particular recommendation emphasizes the need for timely application of foliar-applied herbicides.

Aaron Hager, a U of I weed scientist, noted that foliar-applied herbicides must be applied before Palmer amaranth plants are taller than 4 inches. “Most weed management practitioners are very familiar with the growth rates of waterhemp and many other weed species, but perhaps they are less familiar with the growth rate of Palmer amaranth,” Hager said.

Cody Evans, a weed science graduate student at U of I, initiated work in the greenhouse to compare the growth rate of waterhemp and Palmer amaranth. “This was not a replicated experiment but simply a demonstration of the relative growth rate differences between these two species,” Hager said.

During the project, both weed species emerged on the same day, and the plants were photographed every other day for a month. Photographs show that Palmer amaranth plants reached a 4 inch height less than 10 days after emergence.

“The growth rate comparison illustrated in the photographs was conducted under greenhouse conditions, but experience suggests that a similar growth rate of Palmer amaranth should be expected under field conditions,” Hager explained. “Timely applications of foliar-applied herbicides require vigilant scouting throughout a large portion of the growing season.”

For the complete publication on the weed science program’s recommendations for Palmer amaranth in Illinois, go to https://uofi.box.com/palmeramaranth2014.