In the Garden:
Western Mountains and High Plains
July, 2007
Regional Report

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Crabgrass is opportunistic and will invade thinning areas of the lawn, especially along the sidewalk.

Invading Annual Grasses

As the summer sizzles in record-breaking heat, conditions are ideal for annual grasses to invade both new and old lawns. These annual invaders grow in one season, produce seed, and die with the first hard frost. They are not persistent perennials, so they can easily be dealt with by pre-emergent control in early spring and with proper management practices in the summer. Some of the most common annual grasses that invade the lawn and landscape include goose grass, barnyard grass, foxtail, and crabgrass.

Where do they come from? Annual grass seeds are everywhere -- in undisturbed soils, open fields and drainage areas, cracks of sidewalks. They are carried by wind, pets, humans, and other mysterious dispersal methods. Once the seeds find their way to lawns, the seeds have ideal conditions to germinate and rear their broadleaf 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. They include both cultural (non-herbicidal) and chemical (herbicidal) techniques. My recommendation is to try the cultural methods of controlling annual grass invaders because chemical methods just don't get to the root of the problem.

Cultural Techniques
Mow as high as is practical during the summer months for the particular grass species present in your lawn. Mow bluegrass, tall fescue, fine fescue and ryegrass at 2-1/2 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 shorter 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 like corn gluten 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. These steps will help keep your lawn healthy so the annual weedy grasses won't get a running start.


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