Controlling Bluegrass in Irrigated Alfalfa

July 1, 2015

Bluegrass is a common weed in irrigated alfalfa that can lower harvest quality and shorten stand life.  Bluegrass competes so well because it likes moisture and has many basal leaves that help it grow rapidly after alfalfa is cut.

Effective bluegrass control requires:

• thick alfalfa stands,
• good water management, and sometimes,
• herbicides. 

It is essential to start with thick stands, both to compete with the bluegrass and to have good yield potential after control is achieved.

The key to slowing down bluegrass invasion is irrigation water management.  Irrigation must be timed so the top several inches of soil are dry at harvest — and they need to remain dry until alfalfa regrowth is several inches tall.  Bluegrass grows slowly in dry soil, but alfalfa roots will draw subsoil moisture, if available, for regrowth. Once your alfalfa gets a little bit of growth, it will compete well with the bluegrass.

If thick stands and water management are adequate, herbicides like Select, Poast Plus, or Roundup may be cost effective to weaken or kill bluegrass.  Apply any one of these immediately after harvest.  Be especially careful using Roundup, though, if your alfalfa isn't RoundupReady.  It should be used only if no new growth has developed from your alfalfa.  Otherwise, plants could be killed.  Of these herbicides, select may work the best and is safe for your alfalfa.

Bruce Anderson
Extension Forage Specialist