| Annual winter weeds germinate in the fall and winter and grow activity in spring. Gardeners are often surprised how quickly these weeds can seemingly pop up overnight in their yards and gardens, being unaware that they may have been growing slowly all winter long. Likewise, after they flower in spring they die and disapear for the summer only to return in fall or winter when new seeds germinate.
Some of the more common annual winter weeds in the Midwest are henbit, deadnettle, common chickweed, annual bluegrass, wild mustards, prickly lettuce, Persian speedwell, horseweed, cheatgrass and rabbitfoot clover. Some people do not consider these plants as weeds, as some can also be used for food or have been used for medicinal purposes.
Deadnettle and Henbit
Deadnettle (Lamium purpureum) and henbit (Lamium amplexicaule) are often confused. These winter weeds are both in the mint family and have square stems with opposite leaves. Both plants have pink/purple flowers and can reach 16 inches high but more commonly reach only about 6 inches high in the Midwest. Henbit has circular or rounded leaves with rounded teath on the leaf margin. Lower leaves have petioles. Upper leaves are sessile—having no petioles. Leaves have a crinkled appearance. Deadnettle has triangular shaped leaves and less deeply lobed than henbit. At times the upper leaves are purple or red. All leaves have petioles with the those on the lower leaves being longest. The leaves are crinkled in appearance. Both plants are decumbant in youth but more upright with age. Light purple flowers appear in whorls in the leaf axis of upper leaves from March to May and are tube-like with 2 lips.
Common Chickweed
Common chickweed is a winter annual with a shallow fibrous root which grows in moist, cool shaded areas. The bright green leaves are about ½ inch long, smooth, pointed at the tip, and elliptic in shape. They are opposite branching, slender, creeping stems which root at the nodes. The white flowers of chickweed are ½ inch in diameter and star-shaped with five deeply notched petals. Flowering occurs from early spring to fall. Chickweed reproduces by seed and rooting at the nodes on prostrate stems. The fruit contains many seeds within a dry capsule which splits when mature, shaking out the seeds onto the soil. Seeds will germinate at any time of the year but particularly in spring and autumn. Seeds are dispersed in mud on footwear and tires as well as by animals. Chickweed is found in turfgrass, nursery crops, cultivated horticultural and agricultural crops. It is a host of several damaging virus diseases of crop plants which can be vectored in the chickweed seeds.
Common chickweed has medicinal and therapeutic uses, is rich in vitamin C and may be eaten as a salad.
Annual Bluegrass
Annual bluegrass (Poa annua) is one of the most common weeds in the United States. It is a native of Europe. Golf courses consider it a particular problem. There is also a perennial-type that plagues them. It is indentified by its "boat-shaped leaf tips which curve up like the bow of a boat". This weed is a true lawn annual. Annual bluegrass is more upright growing (growing 3-12" high) and can be noticed by its pale green spring appearance, and by its production of more seeds. It can produce 100 seeds in 8 weeks. It germinates when the temperature falls below 70 degrees and throughout the winter. It usually dies in the summer.
Prickly Lettuce
Prickly lettuce (Lactuca serriola) is in the aster family. It can grow up to 5’ tall. Sometimes this winter weed can be a biennial, and hangs on for 2 years. It has creamy yellow aster-like flowers Lepidoptera (butterfly) larvae feed on this plant. Alternate leaves branch off the main stem. There is a prominent midvein on each leaf which contains a row of spines on the bottom surface.
Several edible lettuces, such as, crisphead, butterhead, cos or Romaine, and loose leaf or bunching, and stem lettuce or celtuce all were derived from this plantl The plant has been used in soap making.
Persian speedwell
Persian speedwell is a winter annual with slender, weak stems that grow prostrate along the ground but turn up at the tips. In shaded areas it tends to grow more upright. The stems are covered with finely pointed, flattened hairs. The hairy leaf blades are oval to roundish with rounded teeth around the edges. The lower leaves are arranged oppositely and occur on petioles, but the upper leaves which occur on the more erect flowering stems are arranged alternately and do not have petioles. The flowers occur singly on long, slender flower stalks which arise from the leaf axils. The small flowers are usually light blue in color with darker blue lines and a pale blue to white center. Prior to flowering, the speedwells are often misidentified as ground ivy, henbit, and purple deadnettle. However, ground ivy does not have hairy leaves and both henbit and purple deadnettle have leaves that are arranged oppositely along the flowering stem. Speedwell is primarily a weed of lawns, turfgrass, landscapes, nurseries, and winter small grains.
Horseweed
Horseweed (Conya canadensis) can grow to 6 1/2 ’ tall. Another common name for this winter weed is mare's tail. A mature plant has leaves that have no petiole (they are sessile). Young leaves are egg-shaped with toothed margins. Mature leaves are oblanceolate in shape (broader and rounded at the apex, and tapering at the base) and are 3-4" in length. Mature leaves are hairy. Leaves are alternate. Plant has a taproot. Small inconspicuous flower heads are at the top of the central stem. Flowers are 5mm in diameter, with white or slightly pink ray flowers. This is a composite flower and there are many tiny disk flowers in the flower head (like daisies and coneflowers). In the early stages, this plant resembles shepherd’s purse or Virginia pepperweed. The fruit (or seed) is a 1mm long achene, it does not split open when it is ripe. It tapers from the apex with many small bristles that aid in wind dispersal. This plant is susceptible to aster yellows.
Cheatgrass
Cheatgrass is a winter annual that has a fine feathery appearance overall, with slender light-green stems drooping at the tips where the seeds form. Seed spikelets and their bristles can be 5 centimeters long. Mature grass grows to 75 centimeters and turns first purple, and then brown, as it dries. Cheatgrass occurs throughout most of the United States and is on state noxious weed lists in 43 states. It grows on rangelands, pastures, prairies, fields, eroded sites and roadsides. Cheatgrass can alter ecosystems by maintaining dominance for years on sites where native vegetation has been eliminated or severely reduced due to grazing, cultivation, or fire. Moreover, it increases the frequency and timing of wildfires. At maturity the sharp-pointed bristly sections can injure wildlife species by working into the nose, ears, mouth, or eyes. Spikelets can also cling to clothing.
Rabbitroot Clover
Trifolium arvense is the Latin name for rabbitfoot clover. This winter weed has a multi-branched growth habit. It is 4-16" tall. It is in the pea family. It came from Eurasia and is naturalized now. Both stems and leaves are densely hairy. Leaves consist of 3 narrow leaflets with minute teeth-like projections at the tip. Flowers are small, pink to purple in color. They are clustered in a grayish soft and silky cylinder shaped heads. It flowers in the spring, and reproduces by seed. Rabbitfoot clover is found in the South East United States, west to Louisiana and north to Missouri. Rabbitfoot clover contributes nitrogen to the soil, as do other clovers, but it grows in unimproved sandy soils in semi-arid grasslands.
Bedstraw
Bedstraw is a winter annual with square stems and short, downward pointing hooks on the stem corners. The stems are weakly branched, prostrate on the ground or climbing on other plants. Bedstraw grows in a tangled mass. The rough hairy leaves grow in whorls of six to eight. Burr-like seeds are produced in pairs and are covered with hooked hairs. The tiny white flowers are four-lobed pointed petals on long flower stalks. Bedstraw is found in moist shady areas, thickets, valleys, roadsides, waste ground, under trees, and clearings. The hooked spines of the stems, leaves and seeds cling to just about everything and are difficult to remove. This clinging characteristic minimized matting when bedstraw was used as a mattress filling. Bedstraw has been used for medicinal purposes for intestinal problems, urinary conditions and skin problems. If the fruit is dried and roasted, it makes a drink, much like coffee.
Shepherd's Purse and other mustards
Shepherd’s purse is a winter annual with erect stems that grow 3 to 18 inches tall from a basal rosette quite similar to that of a dandelion. The rosette grows to be 4 to 8 inches in diameter. Shepherd’s purse has alternate leaves with the lower leaves more deeply lobed than the upper leaves. The flowers are small and white, appearing in clusters at the top of the stalk from early spring to early winter. Each flower develops into a heart-shaped or triangular seedpod which, when the pod dries, splits in half releasing the mature seeds. The seedpods are supposed to resemble the purses of ancient shepherds. Shepherd’s purse does its best in sunny, rich, disturbed soil, but it will also grow in partly shaded, extremely poor soils because insects get stuck on its sticky seeds and provide the plant with extra food. It can be found in flowerbeds, lawns, sidewalk cracks and along the edges of sidewalks and paths.
People have been eating this mustard plant for thousands of years and it is one of the earliest wild greens in the spring. It is edible in the early spring while the basal leaves are still young and tender, before the plant flowers. The whole plant in flower is used (except the roots) in the form of a tea or infusion for medicinal purposes.
Integrated Pest Mangement Strategies
1. Encourage the grass. Keep lawn areas thick and mulch flowerbeds to help prevent weed seeds from germinating.
2. Removal. Dig or pull the weeds in the winter or spring before they flower and set seed for the next year.
3. Good culture. Use good cultural practices to prevent the spread of weeds. Small weed seeds can be spread by machines, clothing, pets, and by contaminated seed.
4. Use chemical herbicides. For established weeds the best time is early spring when the weeds are actively growing but before they go to seed. Herbicides containing Dicamba and/or MCPA or MCPP are more effective than 2,4-D alone. After you have identified the weed you have check product labels or resource materials to see which herbicides are most effective for that weed or combination of weeds. Use herbicides with caution around other desirable plants that may be damaged. Read label directions and cautions carefully.
5. Use pre-emergent herbicide. To prevent germination of the seeds of these winter annuals, apply a pre-emergent herbicide, such as, Gallery in late summer or early fall before the weed seeds have germinated. |
