Summer Annual Broadleaf Weeds

Text adapted from Turfgrass Pest Management Manual: A Guide to Major Turfgrass Pests and Turfgrass
North Carolina Cooperative Extension Service

Summer annual broadleaf weeds emerge in the spring or early summer, grow during the summer and produce seed in mid- to late-summer. Midsummer rains frequently encourage germination. Prostrate spurge may flower within 3 to 4 weeks after emerging in mid-summer. Prostrate spurge, prostrate knotweed and lespedeza can survive close mowing because of their prostrate growth habits.

Weed Management Practices

Maintain a dense actively growing turf through proper mowing, fertilizing and watering practices. Mow at the proper height for your selected adapted turfgrass. For example, mowing a bluegrass/tall fescue mixture at less than 2 inches will encourage the encroachment of summer annual broadleaf weeds as well as grassy weeds. Some summer annual weeds, like prostrate spurge, can be effectively controlled with preemergence herbicides which also control crabgrass before the seeds germinate. Prostrate knotweed competes most effectively in compacted soils.

Coring and traffic control reduce compaction and encourage desirable turfgrass competition. Spray infested areas with a selective broadleaf postemergence herbicide when the weed is young, usually three to four leaf stage. It is best to control summer annual broadleaf weeds in late spring or early summer when they are in the young development stage. They are easier to control at that time and both warm-season and cool-season turfgrasses have a greater chance to recover the areas previously occupied by weeds.

Prostrate Knotweed [Polygonum aviculare L.]

Prostrate knotweed is a low growing annual. It is a very competitive weed in infertile and compacted soils and often invades turfgrasses along driveways, sidewalks and beaten paths across lawns. The tough wiry slender stems radiate from a central tap root and produce a tough mat-like growth. Leaves are dull, blue-green, oblong in shape, smooth, alternate with a membrane at the base sheathing the stem. The tiny white flowers are inconspicuous and are borne at the nodes. It germinates with the first warm temperatures in the spring. Newly emerging seedlings are often mistaken for grasses in very early stages of development.

Lespedeza [Lespedeza striata (Thumb.) H. & A.]

Lespedeza is a dark green, wiry annual with trifoliate leaves. Several wide-spreading prostrate branches come from the slender taproot. It grows close to the ground and seldom is cut by a mower. It is a very common summer weed, choking out thin turf. Hairs grow downward on the stem. Leaves are composed of three leaflets. Stipules are light to reddish brown. Small single flowers arise from the leaf axils on most of the nodes of the main stems and are pink or purple.

Prostrate Spurge [Euphorbia supina Raf.]

Prostrate spurge is a summer annual with a tap root. It branches freely from the base. The reddish or green prostrate stems form a mat-like growth which often chokes out desirable turfgrasses. When the stems are broken they emit a milky juice. The leaves are opposite and vary in color from a pale reddish green to a dark green but usually have a conspicuous maroon blotch. The leaves are smooth or sparsely hairy, toothed especially near the tip and unequally sided at the base with a short petiole. Flowers are very small, pinkish-white, inconspicuous and borne in the leaf axils. The fruit, a three-lobed capsule, develops rapidly.