Quackgrass (Elymus repens) is a cool-season perennial grass, generally found in vacant fields or along roadsides that are not regularly mowed. It is a common weed problem in turf, where this sod-forming grass spreads vigorously by rhizomes (Figure 1), producing allelophatic compounds and forming dense patches that can crowd out desirable grasses (Figure 2). Quackgrass can also be found in agronomic crops such as corn, soybean, and alfalfa. If you go back through historical records of crop production challenges in Indiana and much of the northern and eastern corn-belt, quackgrass is mentioned frequently as one of the top 5 most challenging weeds to control. With the introduction of the postemergence grass herbicides in soybeans in the 80’s, POST grass corn herbicides in the late 80’s and the Roundup Ready technology in the mid 1990’s, quackgrass control was rarely mentioned as a problematic weed. However, this spring we have received multiple phone calls with questions about quackgrass control in row crops. So we thought this might be a good time to review what we know about quackgrass. This article provides information on the biology and control of quackgrass in corn and soybean.
Figure 1. Quackgrass rhizomes. (Photo Credit: Dr. Aaron Patton)
Figure 2. Quackgrass patch. (Photo Credit: Dr. Aaron Patton)
Biology and Identification
Quackgrass is a perennial weed and reproduces by seed and by rhizomes (Figure 1). Quackgrass likes cool weather and is usually up and growing vigorously in April in Indiana. Quackgrass can be easily differentiated from other grasses due to the presence of clasping auricles (Figure 3) and the production of underground vegetative structures such as rhizomes. The rhizomes facilitate the spread of quackgrass throughout the field, but it also reproduces by seeds (Figure 4). Seed production generally begins around June.
Figure 3. Clasping auricles on quackgrass. (Photo Credit: Dr. Aaron Patton)
Figure 4. Quackgrass seedhead. (Photo Credit: Dr. Aaron Patton)
Control
Tillage is not an effective practice for quackgrass control unless aggressive tillage is supplemented with herbicides, as any type of soil disturbance near a quackgrass patch will break up rhizomes and spread them out over a larger area of the field. Therefore, systemic herbicides that can translocate to the rhizomes are the most effective tools for control of quackgrass in row crops. In corn, herbicides such as glyphosate (Roundup PowerMax) and nicosulfuron (Accent) applied POST provide excellent quackgrass control. Atrazine applied PRE in corn can also suppress quackgrass growing from seed. In soybeans, glyphosate and ACCase inhibitor herbicides (group 1) such as clethodim (Select MAX), fluazifop (Fusilade DX), and quizalofop (Assure II) result in excellent quackgrass control. It is important to note that quackgrass plants will need to be actively growing at the time of herbicide application for the herbicides to reach the rhizomes. Additionally, multiple herbicide applications may be required to completely eliminate quackgrass from a field.
References
Patton and Law (2020) Quackgrass. https://turf.purdue.edu/quackgrass/?cat=52 Accessed on May 12, 2020.
