Summer annual grasses are a pervasive weed problem in many turfgrass areas in the Lehigh Valley, with the most common being crabgrasses (Digitaria spp.) and goosegrass (Eleusine indica).

Control of these weeds can be obtained by cultural methods, provided that the life cycle of the plant is understood.

Two species of crabgrass, the hairy or large (Digitaria sanquinalis) and the smooth or small (Digitaria ischaemum), are true summer annuals. Seed germination ranges from mid-spring to mid-summer. All plants are killed by frost in the fall.

Flowering and subsequent seed set take place from mid-summer to early frost and are the means of continuing the species. Abundant quantities of seed are produced, depending on the general health and vigor of the plants.

Once established, crabgrass tolerates high temperatures, compact soils and dry soils better than most turfgrasses.

Goosegrass, also known as silver crabgrass, is often mistaken for crabgrass.

Like smooth and hairy crabgrass, it is a summer annual, but germinates four to six weeks later than crabgrass.

Goosegrass is characterized by fibrous roots and very flattened sheaths that have a silvery-green color, especially near the center of the plant. It has fingerlike seedheads bearing seeds with a zipper-like appearance on the seed stalk.

Goosegrass grows well on heavily compacted soils.

Turfgrasses that are not adapted to the environmental conditions and intended use of the turf may become weak and result in a thin stand. When there are voids in the turf, weeds have an opportunity to grow and compete with the desirable species. The use of proper establishment procedures helps ensure a dense turf that will compete with germinating weed seedlings.

Inadequate liming and fertilization lessen the competitiveness of turfgrasses, resulting in reduced density and subsequent weed invasion. Complete soil testing is the key to proper liming and fertilization.

Adequate nitrogen should be supplied to favor the desirable species.

Phosphorus fertilization increases seedling vigor and is one factor in reducing weed infestations in newly established turf.

Liming keeps the soil from becoming too acid.

Improper mowing is one of the most common causes of weed invasion. Mowing heights that are too short result in weakened turfgrasses; cut at least three inches or higher.

Summer annual grass weeds are extremely opportunistic, filling in voids in turf caused by diseases and insects.

Diseases can be controlled by cultural practices and with fungicides. Insect damage can be reduced by maintaining a healthy turf and using biorational means of control.

Any management practice that increases the density and vigor of desirable turfgrasses tends to discourage competition from weeds. Cultural practices for the control of summer annual grass weeds are aimed at shading and crowding the young weed seedlings by producing a dense sod.

Improving turf density through fertilization, irrigation during dry conditions, and using turfgrasses well-adapted to site conditions will help reduce crabgrass infestations. Keeping lawn mowing heights at about three inches and mowing on a regular basis will help deprive young emerging crabgrass plants from obtaining light, thus reducing populations in lawns.

Of course, there is pre-emergent and post-emergent chemical control. Chemical weed control with herbicides can help produce a quality lawn. It should not be undertaken unless accompanied by an adequate management program designed to prevent re-infestation.

To use herbicides safely and successfully, read the manufacturer’s label carefully and follow all directions.

Hypertufa Leaf Casts: Lehigh and Northampton Master Gardeners will present a workshop on making Hypertufa Leaf Casts, 9:30 a.m. - noon Aug. 17, Louise Moore Park, 151 Country Club Road, Easton. To register:

https://extension.psu.edu/making-hypertufa-leaf-casts

“Growing Green” is contributed by Diane Dorn, Lehigh County Extension Office Staff, and Master Gardeners. Information: Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-813-6613