ANNUAL
RYEGRASS AND ANNUAL BLUEGRASS
Annual ryegrass (Italian ryegrass) and annual bluegrass (poa annua) are grasses that can pose special weed problems in some lawns. These grasses display one common characteristic, which is an inability to tolerate hot weather well.
Annual ryegrass is a yellow-green, coarse-bladed grass that is a common contaminant of even the highest quality turf-type Tall Fescue seed lots. It matures fast into a large, steamy plant. When mown at normal lawn cutting heights, almost all of the leaf tissue is removed, leaving coarse , brown stems showing. While it is an annual , the Italian ryegrass plant is actually capable of surviving for as long 2-3 years under some circumstances. There is no selective control for it. Annual ryegrass will "mow out" over time, and can be both masked and crowded out by seeding with desirable turf species. It can be killed by wick application of a non-selective herbicide such as "Roundup", but the process is time consuming and risky to the desirable grasses intermingled with the annual ryegrass.
Poa annua is a very low-growing, fine-textured, apple green annual grass. The surface of the leave blades is wavy. It prefers well irrigated, highly fertilized soils. It is easy to distinguish in the lawn by its prolific production of white, fluffy seed heads that grow so low to the ground that they escape the mower. This is usually most evident in late-April through May. Once established, annual bluegrass can become the dominant species during the spring in large areas of a lawn. It dies out quickly at the onset of hot weather, and those same areas will become bare. When cool weather returns, new plants germinate from seed. By the following spring, the areas are again so dense and competitive that seeds of desirable species are unable to establish.
Annual bluegrass can ultimately be controlled by several years of consecutive pre-emergent herbicide applications made during the late-summer/early-fall. Then the treated areas can be re-established by a late spring over seeding with desirable turf grass species. Any surviving annual bluegrass plants should be raked out prior to the seeding. In addition to the described pre-emergent herbicide applications, rough bluegrass must also be sprayed in the spring with a non-selective herbicide such as Roundup to kill the already established plants prior to the spring seeding.
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