The use of trade names or products does not indicate the promotion of products, these are strictly used for educational purposes. Information has been adapted from the 2022 Guide for Weed, Disease, and Insect Management in Nebraska.
Summer annual grasses are tough weeds to deal with, especially in perennial systems like pasture or hay fields. They can take advantage of the smallest opportunity to invade and once established, are hard to control. Proper management requires the right timing and patience.
Species like foxtail, sandbur, and crabgrass are annuals that often begin growth after other perennials, grow fast, and quickly set seed. This life cycle can make control difficult. In many circumstances, cultural practices like timing of hay harvest or grazing management may offer the most cost and control effective option. If herbicide control is decided upon, there are a few options to choose from. Once alfalfa is up and growing, the list gets even shorter.
In Roundup Ready® alfalfa stands, treatment is pretty straight forward, by using an alfalfa approved glyphosate product. Label guidelines do recommend treating before weeds exceed 6” in height. It is important to make applications before the alfalfa canopy begins interfering with spray pattern and distribution of product.
Straight alfalfa stands may use grass selective products like Select Max®/Arrow® or Poast®. Recommended weed height will vary depending on product, target, and rate so be sure to follow the label recommendations. Pursuit®, Prowl H2O®, and Warrent® may be an option to consider here for added broadleaf control. Warrent® and Pursuit® are recommended for seedling or newly established stands while Prowl H2O® is recommended for both new seedings and established alfalfa stands. As with Roundup®, canopy cover can interfere with spray distribution, so applications following harvest are recommended.
A different option may be Gramoxone®. Paraquat herbicides like Gramoxone® are non-selective, burn down products, so any green plant material will be damaged. However, if used immediately following harvest when alfalfa regrowth is limited, you may get control of annual species with a minimal yield reduction.
For alfalfa/grass mixtures, things get a bit more difficult. In some cases, previously growing plants can handle some pressure from pre-emergence herbicides. While a slight yield hit can occur, the newly germinating grass seedlings are getting it much worse, so control can be effective. A pre-weed-emergence application of Prowl H20® may do the trick, but needs to be timed appropriately.
Although it may be tempting to start applying right away, we need to wait. Just like our seeded crops, these weeds need a certain sustained soil temperatures to begin germination. For crabgrass, soil temps need to be sustained at 55°F, for foxtail 60°F, and for sandbur its 65°F. Start monitoring soil temperatures and when the appropriate threshold for the species you want to control is crossed, we can get ready to apply.
As with any pre-emergent herbicide, yearlong control may require more than one application. However, a second application may come into conflict with maximum annual application amounts, so be sure to check with the pesticide label before reapplying.
For all herbicides, keep an eye on any harvest restrictions. The pre-harvest interval will vary depending on what product you use.
Summer annual grasses in forage crops are not the easiest weed to deal with, but with the right product, a bit of patience, and proper timing, it doesn’t have to be a problem we can’t control.
-Ben Beckman is a beef systems Extension Educator serving the counties of Antelope, Cedar, Knox, Madison, and Pierce. He is based out of the Cedar County Extension office in Hartington. You can reach him by phone: (402) 254-6821 or email: ben.beckman@unl.edu .