At low elevations, ryegrass should die out by mid-June. It can persist in shady areas where the bermuda is weak and soil moisture is not limiting. At high elevations it will remain for a long time. Annual ryegrass is Lolium multiflorum . It is a true annual, in that it will die after one season, no matter where it is grown.
Annual ryegrass is used for overseeding at low elevations in the late summer, early fall.
Annual ryegrass is much lighter in color and has much wider leaves than perennial ryegrass. The leaves are further apart on the stem. This is why annual ryegrass requires a higher base mowing height than perennial ryegrass. There are varieties of annual ryegrass on the market and they are usually used for forage purposes. Left-over seed is sometimes sold for lawn purposes.