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A Review of Early-Season Weed Species

April 20, 2001
No-till fields are rapidly "greening" from the growth of winter and early- summer annual weed species. A brief review of several of these species might prove beneficial for those attempting to identify what's currently growing in the fields. For those who have access to this newsletter via the Web, color pictures of many of these species accompany this article.

Henbit (Lamium amplexicaule) and purple deadnettle (L. purpureum)

are close relatives; both exist as winter annuals and have square stems. Henbit

is more commonly found throughout Illinois, while purple deadnettle appears more often in the southern half of the state. The lower leaves of henbit are petiolate (attached to the stem with petioles), while the upper leaves grasp the stem (i.e., lack petioles).

The upper leaves of purple deadnettle, however, are attached to the stem with petioles, more triangular than those of henbit, and less deeply lobed.

As the name implies, purple deadnettle has a distinctive reddish to purple coloration of the foliage and stem.

Mustard (Brassicaceae) is a family of many species, but several dominate the Illinois scene. Mustards are often divided by flower color. Wild mustard and yellow rocket

have showy, yellow flowers,

while shepherd's purse,

field pennycress,

and pepperweeds (Virginia and field)

have smaller white flowers. While Illinois has several other mustard species, these are probably the most commonly encountered mustards in no-till production systems.

One plant that is often mistaken to be a mustard species is butterweed (Senecio glabellus), which belongs to the Aster (Asteraceae) family.

Butterweed has bright yellow flowers and exists as a winter annual, so it often flowers close to the time the true mustards flower. All mustard species have flowers consisting of four petals (either yellow or white), while butterweed has a disk array of petals.

The stem of butterweed is hollow

and often has a reddish or purple color.

Chickweed is often used to refer to two distinct species. Common chickweed (Stellaria media) exists primarily as a winter annual,

while mouse-ear chickweed (Cerastium vulgatum) is a perennial species.

Chickweeds are similar in appearance, but mouse-ear chickweed leaves and stems are densely hairy, whereas common chickweed plants lack hairs. Mouse-ear chickweed is also able to root at nodes of the stems. Common chickweed is more common (hence, the name) than mouse-ear chickweed, but both species occur throughout Illinois. These species can form dense "mats" in no-till fields if not properly controlled that can make planting operations difficult.

Horseweed (Conyza canadensis), or marestail, exists as a winter or early-summer annual species. Seedlings develop a basal rosette of leaves, and the leaves are covered with short hairs and have toothed margins.

Control of this species with burndown herbicides can be difficult, especially if applications are made under cool conditions or without 2,4-D.

A description of kochia

biology and management appeared in issue no. 3 of the Bulletin.

A species that is not as common as others described here, but can be difficult to manage with burndown herbicides, is star-of-Bethlehem (Ornitho-galum umbellatum). This species is a bulbous perennial, which is frequently sold as an early-flowering ornamental but which has escaped into agricultural fields. All parts of the plant are poisonous if ingested. Emerging star-of-Bethlehem shoots resemble wild garlic or wild onion but lack the characteristic odor of these species. The mature leaves are dark green and frequently have a prominent white midrib. Plants typically produce bright white flowers

beginning in early to mid-May and then die back for the remainder of the season.

Pineapple-weed (Matricaria matricarioides) is a low-growing winter or early-summer annual species that produces a pineapple-like fragrance when the foliage is crushed. The leaves are finely divided and succulent.

Rounded or conical flower heads consist of greenish yellow tubular flowers and are produced on short stalks.

Dandelion (Taraxacum officinale) is a simple perennial species that forms a large, often deeply rooted taproot.

Leaves have irregular margins, are often deeply lobed, and form a basal rosette. The flower is large and yellow. 2,4-D is often used for burndown control of dandelion, but control is generally more complete and consistent when 2,4-D is applied in the fall.

Several species of buttercup (Ranunculus spp.) exist in Illinois. Some exist as perennials, but many are annuals that can be found in no-till fields.

Flowers generally consist of bright yellow petals.

This list of early-season weed species by no means covers the entire spectrum of species that occur in no-till fields. Other early-season broadleaf species that can frequently be found include prickly lettuce, speedwells, smartweed spp. (Pennsylvania smartweed, knotweeds, wild buckwheat, all of which have an ochrea), common lambsquarters, fleabanes, catchweed bedstraw, plantains, and evening-primrose. Early-season grass weed species include downy brome, cheat, giant foxtail, foxtail barley, and annual bluegrass. For burndown herbicide efficacy ratings on many of these weed species, refer to Table 6, issue no. 2 of the Bulletin.--Aaron Hager and Christy Sprague

Author: Aaron Hager Christy Sprague

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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