In the Garden:
Western Mountains and High Plains
Crabgrass will begin its invasion by creeping from the edge of the lawn, then advance inwards.
Annual Grasses Invade New and Established Lawns
Goose grass, barnyard grass, foxtail, and crabgrass. As the summer sizzles in record-breaking heat, conditions are ideal for annual grasses like these to invade both new and established lawns. These annual invaders are what they are, ANNUALS: grasses that grow in one season, produce seed, and die with the first hard frost. They are not persistent perennials, so can easily be dealt with by pre-emergent control in early spring and with proper management practices in the summer.
Where do they come from? Annual grass seeds are everywhere; in undisturbed soils, open fields and drainage areas, cracks of sidewalks, airborne, carried by pets and humans, and other mysterious dispersal. Once the seeds find their way to lawns and newly sodded lawns, the seeds have ideal conditions to germinate and rear their broad leaves that stand out over the rest of the lawn.
How to Control Annual Grasses
There are several approaches to managing annual grasses in the home lawn. Since it is too late for effective herbicidal controls, cultural controls are most effective in the summer.
Mow as high as practical during the summer months for the particular grass species present in your lawn. Mow bluegrass, tall fescue, fine fescue and ryegrass at 2 to 3 inches during the summer. The seeds of some weeds require high light intensity to germinate. The shaded environment near the soil surface in a high-mown lawn helps deter weed seed germination. In addition, the higher mowing height produces a healthier grass plant. Crabgrass and other annual grassy weeds are much more common and aggressive in lawns that are mowed less than 2 inches.
Mow often enough so that no more than one-third of the grass blade is removed in a single mowing. Letting grass grow tall and then cutting it back to a low height reduces turf density. This is especially important in the spring, when the grass is growing faster. A lawn may require mowing every three to five days during the spring and early summer.
Irrigate properly to help reduce annual weed infestation. Light, frequent irrigation encourages weed seed germination, even if a pre-emergent herbicide has been applied.
Fertilize according to the needs of your lawn species.
Core-aerate the lawn at least once a year to reduce compaction and to control thatch.
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