Pleasant fall weather in many parts of the country could have a downside for alfalfa growers next spring in the form of winter-annual weeds, says Bruce Anderson, forage specialist with University of Nebraska Extension.
“Check your fields and you might find lots of small henbit plants or mustard rosettes or short grass seedlings of downy brome,” says Anderson. “This robust start suggests heavy weed growth next spring. If left uncontrolled they could grow rapidly, reducing alfalfa yield, thinning stands and lowering forage quality.”
Spraying fields now, before soils freeze up, can stave off weed infestations next spring, Anderson says. “Probably the three best herbicides to use right now are metribuzin, Sinbar, and Velpar. All three do an excellent job of controlling pennycress, mustards, and downy brome. Raptor might be a better choice, though, if henbit is your biggest problem.”
“You can wait and be successful with spring spraying” while keeping fall herbicide costs down”.
(Source – http://www.farms.com/news/control-weeds-in-fall-to-benefit-spring-alfalfa-68385.aspx)