Controlling Grassy Weeds in Bermuda Stand

During this time of the year, I spend a lot of time talking to livestock owners and hay farmers about how to control weeds in their Bermuda fields. I still get the occasional call about broadleaf weeds here and there – things like dogfennel, pigweed, horse nettle, etc. – but mostly I get asked about grassy weeds.

“Grassy weeds” is a general term for weeds that are either a true grass (such as Bahia grass or crab grass) or are so similar in appearance and growth habit (such as nutgrass or sandspurs) that effective chemical control is harder to achieve than with broadleaf weeds.

Since these plants are so closely related to Bermuda grass it is much harder to achieve a chemistry that will kill or suppress the target grass and not also hurt the Bermuda. The timing of product application is much more critical and the cost is often much more significant.

Here are some of the more commonly used grass control products labeled in NC and some strategies to best use them:

Roundup– while Roundup (Glysophate) is a staple in a late winter/Spring burndown spray (although with less efficacy over time), it has some limited uses in the summer growing season. One example is for early season control of crabgrass in hayfields when sprayed immediately after the first cutting, 1-3 days post-baling. This will not give season-long control of crab by any means, but you can burn the Crabgrass back for several weeks and moderately clean-up your second cutting.

Pastora – (Nicosulfuron & Metsulfuron) Pastora has several uses for grass control. The Metsulfuron component will help to suppress Bahiagrass during the season, especially if applied April/May. The bigger advantage with Pastora is the post-emergent control of both Crabgrass and Sandspurs. Both of these weeds can be controlled with Pastora IF you time the spray quickly after these weeds emerge in the Spring. If sprayed when they are less than 2” or at the first 1-2 leaves stage you can control the first flush effectively. However, if you wait and let these weeds get over 2” effective control decreases rapidly. The most difficult part of this is identifying either of these weeds that early.

Additionally, Pastora is effective on Vasseygrass, especially if mixed with 6 ounces of Glysophate. Unlike the early spring applications with other grasses, Vasseygrass needs to get some size to it before being sprayed. Waiting until July or even August so the spray gets maximum surface area contact with the plant is the most effective time. It may take up to two years’ worth of spraying to fully control Vasseygrass.

Panaromic/Impose/Journey – (Imazapic) Any of these Imazapic products will give pretty reliable post-emergent control of a broad spectrum of broadleaf and grassy weeds – including sandspurs, crabgrass and sedges.

So, for a field that is wrapped up in all types of weeds, this is a good fallback option. However, the downside of this chemical is that it causes significant damage to and growth suppression of Bermudagrass. Bermuda will be yellow and stunted for at least three weeks post application. Imazapic should not be used on first year Bermuda stands, and should only be applied to healthy, actively growing Bermuda that is not drought stressed.

Outrider – (Sulfosulfuron) this is a product that is narrower in what in controls but gives good results for certain species. Nutsedges, Kylinga species and Johnsongrass are all very effectively controlled with Outrider. One note when using Outrider for Nutgrass control; two applications 4-5 weeks apart will give better long-term control than a single application.

Pre-emergents- Prowl H2O & Rezilon – pre-emergent products are very effective on annual species like ryegrass, crabgrass and sandspurs if applied prior to these species germinating. For summer grasses like Crabgrass, a late-winter/early spring application can give good control for most of the following growing season. Often the active ingredient will run out by the end of the season, but these products will usually give you 2 clean cuttings of hay. Both Prowl H2O and Rezilon are similar in their application windows and timing but each have minor differences discussed below:

Prowl H2O (Pendimethalin) can be difficult to apply as it is very weather dependent. Prowl needs to be watered-in (rain or overhead irrigation) to get into the soil to work. Unfortunately, this rain event needs to happen no more than 48-72 hours after application as Prowl breaks down quickly in the sun. Applying in the rain is not a good strategy as it will decrease efficacy, so timing your spray event right ahead of a rain is a critical, and often difficult, factor when using Prowl.

Rezilon is also weather dependent and must have a rainfall to be activated but it does not have the photosensitivity issue like Prowl does, so if you miss a rain shower for a week or two after application Rezilon will still be partially effective. One downfall Rezilon does have, however, is it restricts newly established Bermuda (1-3 years post sprigging) from sending out runners (Rhizomes). Horizontal spread is critical for Bermuda to establish in a field so Rezilon should not be used until a stand has fully filled-in.

Disclaimer: The use of brand names and any mention or listing of commercial products or services does not imply endorsement by North Carolina State University or discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product before applying any chemical. For assistance contact a Scotland County Cooperative Extension Agent.