Contributors: R.K. Jones, Extension Plant Pathologist; W. M. Lewis, Extension Crop Science Weed Specialist
Management Practices
Establishing a dense, vigorous turf is the best way to reduce the encroachment of winter annual weeds. First, select adapted turfgrass cultivars for your area and then properly fertilize, mow and water to encourage dense growth. Watering scheduled to meet turfgrass needs helps to minimize chickweed competition.
All of the winter annual weeds described, with the exception of corn speedwell, may be controlled with selective broadleaf postemergence herbicides if the desired turfgrass has tolerance. When controlling several different weeds, it may be desirable to select a combination product which is a mixture of two or three broadleaf herbicides. For corn speedwell, repeated application of a three-way combination product at one-half the label rate applied 10 days apart provides good control. This treatment is also effective on parsley-piert and spurweed.
In dormant bermudagrass golf fairways, several herbicides which have both preemergence and postemergence activity may be applied to control winter annual broadleaf weeds and annual bluegrass. Also, non-selective postemergence herbicides are available for controlling these weeds in completely dormant bermudagrass.
The best time to apply herbicide to winter annual broadleaf weeds is from February through April--depending on the turf, location within the state, temperature and growing conditions. In warm-season turfgrasses, winter annual broadleaf weeds should be sprayed while the turf is still dormant and before spring green-up occurs. Spray before resumption of spring growth in cool-season turfgrasses. By spraying at these times, the turf has a greater chance of growing into those areas previously infested with weeds. Certain preemergence herbicides may be used to control chickweed in areas where reseeding or overseeding of turf is not planned. These are applied in the fall prior to expected germination of chickweed which is encouraged by cool temperatures and adequate moisture.
Hairy Bittercress [ Cardamine hirsuta L.]
Hairy bittercress is a winter annual with erect stems 3 to 9 inches tall. Leaves are mostly on the lower portion of the stem in a basal rosette, deeply lobed, bearing a few minute hairs at the base of the leaf and occasionally on the upper surface of the leaf. Small flowers with four white petals occur in dense clusters at the end of branches. The fruit, which is a capsule, develops rapidly and is about 3/4 inch long and 1/32 inch wide.
Buttercups [ Ranunculus species].
Two of the common winter annual buttercups found in the state are smallflower buttercup [ Ranunculus abortivus L.] and short buttercup [ Ranunculus parviflorus L.] which differ considerably in their vegetative characteristics. Small-flower buttercup is an erect, hairless plant. Most of the lower leaves are unlobed with scalloped margins and long petioles. The upper leaves are deeply dissected. The tiny flowers have five yellow petals about 1/8 inch long. A single flower is borne on a stalk in the axils of the upper leaves. Flowers produce a cluster of teardrop-shaped seeds which have somewhat flattened, smooth sides and a straight or slightly curved beak.
Short buttercup is a soft hairy plant that branches freely. The lower leaves are three-to five-lobed or cleft and bluntly toothed on the edge with long petioles. A single inconspicuous flower is borne on an upper node. Flowers have five yellow petals about 1/16 inch long. The teardrop-shaped seeds have minutely spiney sides and a hooked beak.
Common Chickweed [ Stellaria media (L.) Cyrillo]
Chickweed is a low spreading winter annual with a weak, shallow root system. The prostrate stems often root at the nodes. Its spreading growth covers adjacent turf and seriously impedes turf growth. Chickweed often forms extensive, dense patches. Leaves are opposite, oval in outline and tapered to a point. Stems have vertical lines of hairs. Small white flowers are borne in clusters at the end of the stems. Flowers have five deeply-notched petals and, though small, are quite noticeable. Numerous seeds are produced which germinate from late fall through early spring.
Mouseear Chickweed [ Cerastium vulgatum L.]
Mouseear chickweed acts as a winter annual in eastern North Carolina and as a perennial in the western part of the state, especially at higher elevations. It has a vigorous prostrate growth habit. Leaves of mouseear chickweed are opposite, oblong, dark green and, in contrast to common chickweed, covered with soft hairs. Hairy stems may creep along the ground and take root at nodes touching the soil. The small, white flowers have five slightly notched petals.
Large Hop Clover [ Trifolium campestre Schreb.]
This is a much-branched winter annual weed. It has a trifoliate leaf similar to white clover. Leaflets have prominent veins and the terminal leaflet of each leaf is on a short stem. Hop clover has short, hairy, reclining, slender stems which are somewhat reddish. Flowers are a bright yellow with numerous closely associated flowers borne in clusters. Each individual flower produces a single seed. Small hop clover [ T. dubium Sibth.] is very similar, but with fewer flowers in the cluster.
Carolina Geranium [ Geranium carolinianum L.]
Also called cranesbill, because the fruits have a conspicuous "cranesbill" beak about ½ inch long, Carolina geranium is a winter annual. The leaves are deeply five to seven lobed and each lobe is again lobed and bluntly toothed. The flower is pink to lavender and borne two to several together on stalks from the upper nodes. It blooms mostly in April and May.
Henbit [ Lamium amplexicaule L.]
Henbit is a very common winter annual weed in turf. Stems grow primarily upright but can root at the lower nodes. It branches freely from the base stems which are square in cross section and green or purple in color. Leaves are rounded, coarsely toothed, hairy, and deeply veined. They are opposite on petioles in the lower portion of the stem. The upper leaves are sessile or clasping the stem. Flowers are in whirls in the axils of the upper leaves. Petals are purple and fused into a two-lipped tube.
Knawel [ Scleranthus annuus L.]
When this winter annual first germinates it may go unnoticed because of its grasslike features. It is a freely branched plant with spreading stems. Leaves, clasping the stem, are opposite, linear, less than 1 mm wide, and sharp pointed. The very inconspicuous flowers are clustered in the leaf axils. They are small, green, lacking petals and somewhat spiny to the touch.
Parsley-piert [ Alchemilla microcarpa Boiss. & Rent. ]
Parsley-piert is a freely branched winter annual 1 to 3 inches tall. Leaves are alternate and palmately dissected or they may be described as three lobed with each lobe again three to four lobed. They may be petiolate or sessile with a cone-shaped toothed portion (stipules) at the base that encircles the stem. The inconspicuous flowers are borne in axillary clusters and surrounded by the stipules. This weed is increasing as an important turf weed.
Corn Speedwell [ Veronica arvensis L.]
Corn speedwell is a small, weak, low-growing winter annual that thrives in thin open turf and often appears in solid stands. The lower leaves of corn speedwell are rounded and toothed, while the upper leaves are smaller and more pointed. The entire plant is covered with soft, fine hairs. The flowers are small, bright blue with white throats and nearly stalkless. The seedpods are heart shaped. Purslane speedwell [ V. peregrina L.], which is a much branched, somewhat succulent winter annual with linear leaves and white flowers, also occurs in the state.
Spurweed [ Solvia pterosperma (Jussieu) Lessing.]
Spurweed is a low growing, freely branched winter annual which usually does not root at the nodes. Leaves are opposite and twice pinnately dissected. The flowering heads are borne sessile in the forks of branches. Flowers are small, l/8 to 1/4 inch, broad and inconspicuous. The seeds have sharp spines, hence the common name. Infestations are increasing in North Carolina, particularly in the southern Coastal Plains and Piedmont.
Johnnyjumpup Violet [ Viola rafinesquii Greene]
This is a winter annual with erect freely branched stems growing 1/2 to 5 inches tall. The leaves are borne alternate on the stem with prominent dissected stipules. Flowers are borne on prominent stalks from the upper nodes. Flower petals may be white with blue veins or entirely bluish to bluish-violet. They appear like a miniature common violet flower.
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