Glyphosate-resistant ryegrass is getting more prevalent in Alabama row crop fields, particularly in no-till and strip-till fields where tillage is not applied intensively. This problem usually starts with a few sporadic patches that cannot be killed with burndown herbicides and slowly progresses to the whole farm.
Here are several considerations regarding this problem:
- Refrain from planting ryegrass as a fall cover crop. Some growers in Alabama spread ryegrass seeds after harvest for use as a cover. This always make me nervous! Seeded ryegrass can evolve resistance to herbicides just like wild populations. There is no guarantee that purchased ryegrass seeds are totally “herbicide resistance free.” You might be planting your own resistant ryegrass seeds without even knowing it.
- Kill ryegrass before seed heads emerge. This prevents ryegrass seed production and elimnates the chance to pass down herbicide resistance to the next generation.
- Once a few ryegrass patches appear that you cannot kill with glyphosate, always use Gramoxone and clethodim to control them. Do not let resistant populations fully establish on your farm; they will be hard to get rid of thereafter.
In this study at Headland, Select Max alone at 12 oz/A with crop oil and AMS only provided around 50% ryegrass control. Therefore, do not expect clethodim to eliminate large ryegrass by itself. Gramoxone and sequential applications will be needed. See the plot images below for effective programs to control ryegrass without Roundup.
There have been multiple reports from the Mississippi Delta and North Alabama regarding ryegrass resistance to clethodim. We do not want to put too much selection pressure on clethodim and lose its efficacy on ryegrass in the near future. If ryegrass pressure is very high, consider an application of Warrant, Zidua or Dual Magnum in early November when ryegrass is germinating.
This is part of a large study funded by the Alabama Cotton Commission to address winter and summer grass control.