PORTAGEVILLE, Mo. — Ryegrass problems in wheat have been increasing in southeast Missouri. The number one thing to remember about ryegrass in wheat is that it is best controlled with a fall application of Hoelon or Osprey. Fall herbicide applications tend to go against our tradition of planting wheat and forgetting about it until February.
Hoelon, the older ryegrass herbicide, it is a grass-only herbicide. It is labeled for pre-emergence application, but the rate is about double the postemergence rate. Therefore the standard and most economical recommendation is for early postemergence application, shortly after wheat emergence.
Don’t tank mix anything with Hoelon (there is an antagonism risk) and don’t add crop oil or other adjuvants (there is a crop injury risk with them). The residual activity of Hoelon generally provides good, season-long control.
A lot of ryegrass in Arkansas and some ryegrass in Missouri is resistant to Hoelon. If you have never used Hoelon before, we wouldn’t worry about resistance. But if you have tried Hoelon and had escapes, your ryegrass may be resistant. Of course, there is a small chance that your ryegrass infestation got started from some herbicide-resistant seed, so be aware of the resistance issue.
Osprey, the other ryegrass herbicide, is relatively new. Like Hoelon, it works best in a postemergence application, shortly after wheat emerges in the fall.
There are two major differences between Osprey and Hoelon: (1) Osprey has some broadleaf activity and (2) Osprey has very little residual activity.
Osprey also has some special adjuvant recommendations. You can use a MSO-type oil or liquid fertilizer, but be sure to follow the label. This is a case where the additive makes a real difference.
For broadleaf weed control, Osprey suppresses a lot of junk broadleaf weeds but really doesn’t provide complete, standalone control. A grower who has a lot of broadleaf weeds should tank mix something with it (Harmony products and Sencor are two good options). As long as garlic isn’t a big problem, these tank mixes can often be a complete weed control program for wheat.
For bad ryegrass problems, Osprey will have inadequate residual activity. The current recommendation is to tank mix 2 or 3 ounces of Sencor. Sencor by itself is a pretty respectable ryegrass treatment. Double-check the Sencor label for crop safety and soil type restrictions.
Growers have wheat weed control options, and there may be some difficult choices: Should you use Harmony in the fall with Osprey or wait until the spring? Every field is different, and there are always tradeoffs.
If you have bad ryegrass, you will need to use Hoelon (for it's residual activity) or you will need to use Osprey plus Sencor. If you have bad garlic problems, you will need to use a ryegrass herbicide in the fall and a Harmony-type treatment in the spring. In our experience, spring applications of Hoelon and Osprey have not been as good as fall applications.
One final comment: growers who have bad ryegrass problems should use all of the old-fashioned management techniques, including starting with a totally clean seedbed.
Andy Kendig is an Extension weed specialist and Anthony Ohmes is a regional Extension agronomist with the University of Missouri.