Hay, Grassy Weeds, and Prowl

As first cutting hay comes off, it is a good opportunity to apply herbicides to control certain annual weed species. We often get a lot of questions about weedy grasses being a problem after first cutting; thus we usually suggest the use of Prowl herbicide or another pendimethalin containing product. But keep in mind that there are different formulations of pendimethalin, namely the older 3.3EC and the newer water-based formulation, 3.8CS. In alfalfa, alfalfa/grass mixes, and grass hay/pasture, the 3.8CS formulations can be used – these include Prowl H2O and Satellite HydroCap. The 3.3EC formulation (Prowl 3.3, Acumen, Framework, Pavilion, Pin-dee 3.3, Stealth, Satellite 3.3, etc.) can only be used in pure stand alfalfa settings and not in mixed or grass-based stands. Do not use the 3.3EC formulation in grass forages since it tends to cause crop injury (leaf burn). As a reminder, pendimethalin (Group 3) provides about 1 month of residual control of many summer annual grasses and some annual broadleaf weeds as they germinate.  It is typically not as effective on winter annual weeds such as annual bluegrass, chickweed, and mustards. It will not control any weeds that have already emerged at the time of application. Adequate rainfall is required after application to activate it. Apply to established alfalfa before weed emergence. Applications should be made prior to the alfalfa reaching 6 inches in regrowth. Some stunting and yellowing of the alfalfa may occur with post applications. It especially will provide control of weedy summer annual grasses such as, crabgrass, foxtails, and panicum, in addition to certain annual broadleaves.

On another note, immediately after the first cutting is a good time to control weeds such as common chickweed and annual bluegrass. Gramoxone SL (and other paraquat products), Pursuit and Raptor are effective on common chickweed (however, if chickweed is ALS-resistant, Pursuit and Raptor will not control it.) And Gramoxone/paraquat is a good option to control annual bluegrass soon after first cutting. Keep in mind it is best to apply these products no more than 5 days after harvest and before 2" of regrowth.