Identify Your Early Season Weeds

April 4, 2010 07:00 PM

Pam Smith, Farm Journal Seeds & Production Editor
Do your fields resemble a garden salad or a colorful floral bouquet this spring? Warm weather in early April encourages of growth of many early-season weed species, especially in no-till fields.
University of Illinois weed scientist Aaron Hager says these annual weeds can sometimes be difficult to identify. In fact, the past few years of wet weather generated enough questions from growers that Hager put together a guide of the major culprits (in the Midwest) that includes a color photograph and text describing 19 species. It fits easily in your shirt pocket and can be ordered by calling 217/333-4424. Or you can view the photos online Identifying Early-Season Weed Species.
When fields take on the yellow tint, you may be dealing with one or more of the weed species in the mustard (Brassicaceae) plant family. "Actually members of this family have either white or yellow flowers that consist of flour petals that form a cross,” Hager says. Some of the more common members found are wild mustard, yellow rocket, field pennycress, Shepherd's-purse and pepper weeds.
Field Pennycress:

Members of the smartweed (Polygonaceae) family that emerge during the early spring are Pennsylvania smartweed, prostrate knotweed and Ladysthumb.
Hager says chickweed exists primarily as a winter annual in Illinois, but it sometimes emerges in early spring. Mouseear chickweed is a perennial covered with dense hairs on the leaf and stem surfaces. Common chickweed lacks hairs. Both can form very dense vegetative mats that make tillage and planting difficult.
Henbit is responsible for painting many fields with a pinkish purple cast. This winter annual with square stems looks a lot like its close relative purple deadnettle. Purple deadnettle has a more distinct reddish coloration of foliage and stem and the leaves are more triangular than those of henbit and less deeply lobed.
When fields are really yellow, there's a good chance it's butterweed (Packera glabella), which is also sometimes called cressleaf groundsel. Commonly found in wet areas, this annual has a smooth, hollow stem that can be either green or bright red in color. Hager says the plant is often mistaken for mustard, but the species actually belongs to the Asteraceae family. Butterweed flowers resemble a daisy or aster.
Kochia (Kochia scoparia) is an early-emerging summer annual. This herbaceous dicot was introduced from Europe as an ornamental because of its red color in late summer and fall and is therefore often called "fireweed.” In the same botanical family as common lambsquarters, but the cotyledons of this plant are hairless.

Horseweed (Conyza Canadensis) or marestail, is a winter or early-summer annual. Seedlings develop a basal rosette of leaves covered with short hairs and toothed margins. Hager says this weed can be particularly difficult to control with burndown herbicides when applications are made under cool conditions or without 2,4-D.
Star-of-Bethlehem (Ornithogalum umbellatum) can also be difficult to manage with burndown herbicides. The bulbous perennial is sold as an early-flowering ornamental, but it has escaped into agricultural fields. All parts of the plant are poisonous if ingested. Emerging shoots resemble wild garlic or wild onion, but lack the odor of these species. Mature leaves are dark green and frequently have a prominent white midrib. Plants typically produce white flowers.
Poison Hemlock:
Poison hemlock (Conium maculatum) is another poisonous plant that is increasing along roadsides and more common in no-till fields. The lacy leaves lead many to mistake this with Queen Anne's Lace, but the leaves of the biennial species are fuller and more toothed. The stem is smooth and hollow with purplish spots or blotches.
Other weeds you might find this time of year are dandelion, prickly lettuce, buttercup, speedwells, annual bluegrass, catchweed bedstraw and plantains.
"Early spring annuals can compete directly with the crop and we recommend farmers take steps to control existing vegetation prior to planting. Selection of a burndown herbicide  should be based on a evaluation of the field and growth habit of the particular weeds,” Hager says.  "Fields with dense infestations of aggressive weed species may warrant burndown applications several weeks ahead of planting to reduce the potential for planting delays. Control in early/mid-April is often more consistent than later in the season. Another advantage of early application is a reduction in weed seed production, therefore possibly reducing infestations in subsequent years.”

You can email Pam Smith at

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