Palmer amaranth has many characteristics that put it in a class of its own among summer annual weeds in the Mid-South. I have heard several weed scientists describe Palmer amaranth as a “super weed” or the “perfect weed.”

Palmer amaranth has a broad emergence window, so it produces multiple flushes. It grows rapidly, which influences its competitive ability with crops. It produces an obnoxious quantity of seed, which allows the weed population to sustain itself over time.

Without exception, if glyphosate-resistant Palmer amaranth is present in a field, then that weed dictates how a herbicide program is designed.

After a few years of trying to develop an economical program for controlling glyphosate-resistant Italian ryegrass, I believe Italian ryegrass has to be close to a “perfect” winter weed.

A typical Mississippi Delta winter is the ideal environment for Italian ryegrass. The 30-year average high temperature at Stoneville, Miss., from Oct. 15 to March 15 ranges from 48 to 76 degrees F. And, the historical low temperature only reaches 32 F or lower during the first two weeks of January.

Italian ryegrass thrives where there are mild climates and fertile soils. It has a low tolerance for both hot, dry climates and harsh winter conditions. The generally mild winter temperatures and rich soils in the Delta provide a perfect niche for Italian ryegrass.

Italian ryegrass exhibits some of the same characteristics as Palmer amaranth, which helps make both of these weeds a top priority in the Delta. Peak emergence for Italian ryegrass occurs in the fall, but it continues throughout the winter with another large flush in the spring.

Italian ryegrass plants also grow rapidly. The extended emergence window and rapid growth complicate herbicide programs targeting this weed. If you treat it in the fall, you may have to spray again to control the spring flush. If you wait and spray in the spring, spray coverage may be poor because small, spring-emerging plants will be mixed in with larger, fall-emerged plants. Also, the fall-emerged plants will have extensive root systems that will help these plants recover from a spring herbicide application.

Palmer amaranth produces male and female plants, so this species must cross pollinate in order to produce seed. Italian ryegrass does not produce male and female plants, but it is an open pollinated species. This means that although it is not a requirement for successful pollination as in Palmer amaranth, two Italian ryegrass plants can cross with another. This genetic mixing between individuals and among different populations can contribute to genetic diversity, which is a prime “weedy” characteristic.