Landscape - Cool Season Annual Grass Weeds in Landscape Beds.

The following is a short article on two common cool season grass weeds found in landscape beds in the spring.

Cool season annual grass weeds in landscape beds.

There are two cool season annual grass weeds that are commonly found competing in landscape beds during the spring. Annual bluegrass is easily identified this time of year by its compact growth and production of many seed heads low to the ground. When annual bluegrass infests ground covers and perennial beds it can form a dense mat that will stunt plantings. Downy brome is another common winter annual grass that is highly competitive in ground covers and perennial beds during the spring. It has a more upright growth and can be identified by its densely hairy leaves and sheaths and drooping oat-like seed heads when mature. Both these species will die out by mid-June. However, they will have reseeded leaving a seed bank for germination in late summer.

Effective control of these grass weeds can be obtained with the use of preemergence herbicides applied in late summer (such as prodiamine). Non selective herbicides such as glyphosate, glufosinate, and pelargonic acid can be used as spot treatments at any time but are most effective on young plants that are not fully tillered. If escapes are found in beds, it is important to control these species in late winter or early spring before they start to produce seed heads. Selective over-the-top postemergence grass herbicides for downy brome in landscape beds include sethoxydim, fluazifop-P-butyl, and clethodim. Only clethodim is effective on annual bluegrass. Large, well tillered plants or plants with seedheads may not be adequately controlled by these materials and may still reseed.

Gordon Johnson, Extension Horticulture Agent, UD, Kent County