Glyphosate resistant ryegrass has been a persistent problem since appearing in almond orchards in the Sacramento Valley in the late 1990’s.  It is a winter annual weed, but under irrigation it can germinate any time of the year.  This year round germination pattern wasn’t noticeable in the Sacramento Valley when it was effectively controlled by glyphosate.  Summer and early fall germinating ryegrass plants are particularly difficult to control at the typical November to December herbicide timings because they are larger established plants at the time of application.

Pre-emergence herbicides are a good way to deal with this extended germination period.  June/July pre-emergence herbicide treatments...