Annual ryegrass has been rearing its ugly head from a weediness perspective as of late. It has become increasingly problematic in Kentucky, quickly becoming a top 3 weed to deal with. It has also jumped the Ohio River and been steadily moving northward through multiple Indiana counties (Fig. 1). We’ve also received several calls and emails indicating a difficulty to terminate an annual ryegrass cover crop. As a result, we wanted to provide an update on herbicide resistance and provide some recommendations for management.
Nationally, ryegrass has been found to be resistant to six herbicide groups including Group 1 (SelectMax, Axial, etc.), Group 2 (Accent, PowerFlex, etc.), Group 9 (Glyphosate), Group 10 (Liberty), Group 15 (Define, Dual Magnum, etc.), and Group 22 (Gramoxone). The majority of these resistance concerns have typically been isolated to the Southern and Pacific Northwest regions of the U.S. However, resistance concerns have gradually been creeping northward.
In Kentucky, ryegrass has been confirmed resistant to Group 1 (Select Max, Axial Bold, etc), Group 2 (Accent, PowerFlex, etc), and Group 9 (glyphosate) herbicide groups with widespread glyphosate-resistance now occurring. Additionally, pinoxaden (Axial) failures have been more heavily reported across the Kentucky wheat growing area. In Indiana, there is not “confirmed” resistance to glyphosate and Group 2 herbicides; however, numerous failure complaints have been received on both groups, and it is highly likely that there are multiple occurrences, particularly in southern Indiana.
In addition to herbicide resistance, other attributes may be contributing to herbicide failures including: improper application setup, late timings, and possibly some overloaded “hot” tank-mixtures causing antagonism issues. Ryegrass is difficult to control to begin with, and each of these things add up to increase the likelihood of a failure occurring. The little things matter for successfully managing ryegrass.
As a result of these challenges, here are a few of the management efforts we’d recommend to getting a handle on any ryegrass problems you may be having. On the plus side with ryegrass, previous research has shown that if we can eliminate seed production from any ryegrass plants for 2-3 years, we can effectively reduce the population in the field by 90%+.
- Use crop rotation, particularly to soybean. This allows for some alternative herbicides to be used such as clethodim (SelectMax).
- Start clean: Make sure to eliminate ryegrass prior to planting. Clethodim (SelectMax) at a minimum of 16 fl oz/ac (8 fl oz/ac of a 2 lb product) can be an option prior to planting soybean; however, it is a challenge prior to corn due to the plant-back restriction. Additionally, even at these higher rates, clethodim tends to be rather slow when applied during cold periods and can allow ryegrass escapes or the need for a second application. Gramoxone can also be effective at controlling ryegrass, but it frequently takes two applications, and we would recommend adding metribuzin or atrazine to the tank-mixture as they will heat up the Gramoxone making it more effective.
- Once corn is up, it becomes extremely challenging to manage ryegrass, and there are minimal options. Group 2 herbicides such as Accent Q or Steadfast Q may work, but in our experiences, it may be a 50/50 chance. Enlist corn may also be an option where we would have the option to use quizalofop (Assure II); however, there are some concerns in heavy wheat growing areas where we’ve had Hoelon (diclofop) resistance for years that this may confer cross-resistance to quizalofop as well. The “best” recommendation we currently have in this situation is to plant corn with the LibertyLink trait, and add at least one application of glufosinate (Liberty) to help beat back the ryegrass in-season.
- Use an alternative fall-planted cover crop like cereal rye. Research has shown than cereal rye is highly competitive and can significantly hinder annual ryegrass growth and seed production, while still remaining easier to terminate in the spring prior to planting the cash crop.
- Consider the use of fall-applied residual herbicides. Herbicides such as Dual Magnum or Zidua have fall application options on their label, and provide effective residual control of annual ryegrass often into the spring months (Fig. 2). Command (clomazone) can also be applied in the fall, and has very good ryegrass control; however, you must plant soybean the following spring as there is a 9-month plant-back interval to corn.
On highly erodible fields, consider a combination of a fall-applied residual and cereal rye cover crop to reduce soil erosion and provide two effective management tactics against ryegrass.
Although these options are not easy, they are effective. And as we stated previously, if we can get ahead of ryegrass seed production, it only takes 2 to 3 years to drastically reduce the soil seedbank and future problems. If you have any problems, questions, or would like to report an area with ryegrass concerns, please don’t hesitate to contact us or your local Extension Educator. Good luck out there!
