Annual Broadleaf Weeds

February 22, 2017

 

Black Medic (Medicago lupulina)

 

Description: This summer annual (or less commonly a winter annual or biennial) member of the legume family (Fabaceae) reproduces by seeds. Black medic is shallow rooted with multi-branched, slender, prostrate, slightly hairy, somewhat square stems spreading 12 to 24 inches. The alternately arranged, dark green leaves are compound with three oval leaflets. The center leaflet is stalked and the side leaflets occur close to the stem. Leaves are sparsely hairy and leaflets are 1/5 to 3/5 inch long. The 1/8 to 1/6 inch long bright yellow flowers are clustered on short stems that emerge from the leaf axis. Each cluster is about a ½ inch long, round and comprised of up to 50 individual flowers. Flowering occurs from April through October. The seedpod is black and tightly coiled. Black medic occurs in a variety of turf settings but does well in nutrient-poor and drought-prone soils.

Control: Maintain density and health of established turf; black medic can be hand-pulled. Apply postemergence broadleaf herbicides during periods of active growth from late spring to early summer and again from early autumn to mid-autumn.

 

 

Common Chickweed (Stellaria media)

 

Description: This cool-season annual member of the pink family (Caryophyllaceae) reproduces by seeds and spreads by creeping stems. This weed may persist through summer in sites protected from heat and drought. Common chickweed is low-growing and can form large, dense patches. The hairy, creeping stems root at nodes and produce shallow, fibrous roots. Leaves of common chickweed are bright green, opposite, simple, broadly oval and usually less than 1 inch long. The margins are entire. The small, white flowers of common chickweed are ½ inch in diameter and star shaped with five deeply notched petals. Flowering occurs during the spring. Common chickweed occurs in cool, moist, shady, often compacted, fertile sites in spring and autumn.

Control: Maintain turf density and health using proper culture; allow turf to dry between waterings; or mechanically remove. Apply postemergence herbicides in mid-spring to early summer and/or mid to late autumn during active growth; apply preemergence herbicides before germination in late summer or early autumn.

 

 

Common Purslane (Wild Portulaca) (Portulaca oleracea)

 

Description: This warm-season annual member of the purslane family (Portulacaceae) reproduces by seeds and spreads by rooting stem pieces. Common purslane germinates late in the season and forms a long taproot with fibrous lateral roots. The stems are succulent, smooth, fleshy, usually purple-red, and may root at lower nodes. The stems are many-branched, reach up to 24 inches long and grow in a prostrate fashion to form mats. The leaves are alternate to nearly opposite, wedge-shaped (rounded at the tip and narrowed at the base), up to 1-1/4 inches long, thick, fleshy and smooth and are often clustered near the ends of branches. The yellow flowers are borne individually in the leaf axils or clustered at the ends of branches. There are five petals. The fruit is a globular capsule. Flowering occurs from July through September. Common purslane thrives in sunny, fertile, sandy soils and can be troublesome in late-summer seedings. It tolerates poor, compacted soils and drought.

Control: Maintain a dense and healthy turf using proper cultural practices. Mechanically remove common purslane but destroy or physically remove the stems as they may root in open soil. Apply postemergence broadleaf herbicides from midsummer to early autumn during periods of active growth; apply preemergence products in mid to late spring.

 

 

Henbit (Lamium amplexicaule)

 

Description: This member of the mint family (Lamiaceae) is a cool-season annual that reproduces by seed and rooting stems. Henbit stems droop and then turn upright to grow to 16 inches. They may root where they touch the ground. They are square, green to purplish, and smooth or hairy. The roots are shallow and fibrous. The ½ inch to 1 inch long leaves of henbit are opposite, dark green and hairy above, lighter below. The lower leaves have petioles and the upper leaves are borne directly to the stem. The leaves are triangular to circular and have palmate venation. The leaf edges have rounded teeth and are crinkled at the edges. Henbit flowers are tubular, pink to red to purple, and borne in whorls in the upper leaf axils. They appear to have two lips and are up to ¾ inch long. Henbit normally flowers from April through June and occasionally in September. It is often found growing in moist, fertile soils.

Control: Maintain density and health of established turf, and avoid thin seedings in the autumn. Small populations can be hoed or hand-pulled. Apply post emergence herbicides from mid to late autumn. Preemergence herbicides should be applied in late summer before germination. Because henbit grows in cool conditions, it can be a problem in warm-season turf.

 

 

Pineapple Weed (Matricaria matricarioides)

 

Description: This member of the aster family (Asteraceae) reproduces by seeds and can live as either a summer or winter annual. Germination can occur as long as conditions are favorable. Plants are low-growing and bushy with young plants forming a rosette. The leaves are finely divided, smooth, thick and hairless. A sweet-smelling odor reminiscent of a pineapple is emitted when plants are crushed. The stems are erect, branched and spreading. The flowers appear May through September as rounded, greenish-yellow heads on short peduncles at the ends of stems. The root is a shallow taproot. Pineapple weed can be found in both high and low maintenance turf. It can tolerate compacted soils and low mowing heights.

Control: Small populations can be removed by hand. Reduce soil compaction; and maintain turf density and health through proper culture. Preemergence herbicides may be used but this weed’s broad germination window may present challenges with proper timing. Apply post emergence herbicides when plants are young and actively growing.

 

 

Prostrate Knotweed (Knotgrass) (Polygonum aviculare)

 

Description: This summer-annual member of the buckwheat family (Polygonaceae) reproduces by seeds. During early spring when germinating, knotweed has long, narrow, dark green leaves and resembles a grass. Later, slender, wiry stems emerge from a thin taproot to form a tough mat. Stems can grow up to 2 feet long. There is a papery sheath (ocrea) at each node, and the nodes are swollen. The leaves are alternate, small, narrowly oval, smooth, dull, bluish green, and up to 1 ¼ inches long and 1/3 inch wide. The flowers are small and borne in clusters in leaf axils. The sepals are white to green, with pinkish margins and occur from June through October. Knotweed is found in compacted, infertile soils or thin turf in sun, often next to heavily trafficked walks or drives or overused play or athletic sites.

Control: Mechanically pull, reduce soil compaction and maintain turf density and health through proper culture. Apply preemergence herbicides in mid-spring through late summer when the plants are young and actively growing.

 

 

Shepherd’s-Purse (Capsella bursa-pastoris)

 

Description: This winter-annual member of the mustard family (Brassicaceae) reproduces by seeds. Shepherd’s-purse emerges from a slender, branched taproot to form a rosette of leaves with this, erect stems growing to about 18 inches tall, usually branched and covered with grayish hairs. The basal leaves are simple, 2 to 5 inches long and variably lobed, serrated or divided. Leaves on the stems are alternate, arrow-shaped and the base extends past the stem. The basal rosettes may be confused with dandelions; leaves of shepherd’s-purse are normally more narrow. Flowers on shepherd’s-purse are small and white, with four petals set in the shape of a cross. They are 1/12 to 1/6 inch wide and occur in elongated clusters at the ends of branches on slender stems. The flowering period is from March to frost and the fruit is a heart-shaped or triangular capsule. Shepherd’s-purse occurs in this turf and among new seedlings; it tolerates saline soils.

Control: Maintain turf density and health through proper culture and use adequate seed to provide seedling density. Hand-pull or mechanically remove before flowering. Apply postemergence broadleaf herbicides during periods of active growth in mid-spring and again during autumn.

 

 

Speedwells (Veronica spp.)

 

Description: Speedwells are low-growing and freely branched. Many types exist. Some of the more common species in Illinois (corn speedwell and purslane speedwell) are winter annuals, but some types are perennial. Flowers occur in the spring; they are small and white, blue, purple or pink. The seed capsule is generally heart-shaped but can be four-lobed on certain types. Leaf margin and arrangement vary according to type. Speedwells are common in lawns, gardens, roadsides and fields and can be a particular problem in spring seedlings. Shade and moisture are favored by several types.

Control: Maintain turf density and health through proper culture and use adequate seed to provide seedling density. Hand-pull or mechanically remove before flowering. Apply postemergence broadleaf herbicides during periods of active growth in mid-spring and again during autumn. Preemergence herbicides can be applied for control of annual speedwells.

 

 

Spotted Spurge (Chamaesyce maculata)

 

Description: This warm-season annual member of the spurge family (Euphorbiaceae) reproduces by seeds. Germination occurs when soil temperatures warm to 60-65 degrees F and can continue as soil temperatures climb to more than 90 degrees F. Spotted spurge develops a central shallow taproot from which prostrate stems forma flat, extensively branched mat up to 2 feet in diameter. The stems exude milky sap when broken. Leave of prostrate spurge are opposite, small, oval and up to 3/5 inch long. They are sometimes purple spotted and/or hairy. The petioles are short. Spotted spurge flowers are very small, inconspicuous, cup-shaped and develop in terminal clusters or leaf axils from June to October. This weed is found in poor, drought-stressed open turf. It germinates and grows well during hot, dry weather on thin soils and is often found on closely mowed sites. Prostrate spurge is very similar and considered by some taxonomists to be the same species.

Control: Maintain turf density and health through proper culture; water deeply, fertilize in autumn and avoid close mowing. Mechanically remove or hand-pull. Apply preemergence herbicides before germination in the spring; apply postemergence herbicides in late spring through midsummer when plants are young and actively growing.

 

 

Robson, D., Wiesbrook, M., Voight, T., Nixon, P., Cleveland, T., & Gill, M. (n.d.). Turfgrass 39-1: Illinois Pesticide Safety Education Manual. Premier Print Group.

 

University of Illinois Pesticide Safety Education Program
 

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