Italian ryegrass has caused significant issues for small grain production in the Piedmont in recent years due to the development of herbicide resistance. Currently, Italian ryegrass can be resistant to up to five different MOA’s, including groups 1 (ACCase inhibitors), 2 (ALS inhibitors), 9 (glyphosate), 10 (Liberty), and 15 (LCFA inhibitors).
Unfortunately, many of the herbicides that producers depend on for ryegrass control fall into these modes of action, meaning we need to be careful not to lean on just on mode of action.
Despite the difficulties, managing ryegrass in wheat is important to achieve high yields. One ryegrass plant per square yard can reduce yield 0.4% in that area. It may not sound like much but it adds up over time, especially in dense ryegrass stands, potentially robbing 75% of the yield in heavily infested areas.
I believe we sometimes also tend to underestimate the negative impacts ryegrass can have on wheat seedlings in the fall. While it may be tempting to save a herbicide application for early spring, a fall herbicide application could be beneficial. Not only is the ryegrass competing with wheat potentially reducing fall growth and tillering, it is also increasing in size thus making future herbicide applications less effective.
Hitting the ryegrass early results in better control due to increased coverage and smaller weed size. Typically the most competitive ryegrass is the ryegrass that germinates in the fall, not the ryegrass that germinates in the spring.
I wanted to put together this information before wheat planting so we can be better prepared and informed about the ryegrass battle this fall/spring.
Some general guidelines for better weed control include:
- Plant quality seed that is free of weed seed.
- Proper liming and fertilization.
- Planting at the proper time, rate, and depth.
- Narrower rows/higher populations can help crowd out weeds.
- Timely and appropriate application of effective herbicides.
Some more specific guidelines for ryegrass control in wheat:
1. Start clean. Don’t plant into existing ryegrass thinking you can get it later. Odds are you may not. If you have ryegrass in the field, a burndown with paraquat may very well be useful.
2. Fall herbicide application may be useful. Zidua (MOA 15) and Anthem Flex (MOA 15+14) are options to control ryegrass emergence. These products can be applied when 80% of the germinated wheat seeds have a 0.5 inch shoot until wheat spiking.
Axiom (MOA 15+5) has shown to give good control of ryegrass emergence as well and must be applied at the wheat spike stage. Finesse (MOA 2+2) can be applied preemergence of wheat, however offers only variable suppression of ryegrass emergence and if soybeans are to be double-cropped, they must be a STS variety.
3. Osprey (MOA 2), Axial XL (MOA 1), and PowerFlex (MOA 2) are the labeled postemergence herbicides for ryegrass control in wheat. There is resistance to each of these herbicide classes in NC wheat so results may be variable at the best. If you need a postemerge application, apply early to small ryegrass that is minimally tillered.
Lastly, keep in mind that Italian ryegrass is only an annual grass. That means that it must set seed each year in order to come back the next. Furthermore, these seeds do not survive long periods of time in the soil. Research has shown that by keeping ryegrass from making seed for only one year results in significant reductions in ryegrass stands the following year.
Anything you can do to keep ryegrass from going to seed will help you going forward.