Winter annual weeds can become a major problem in crop production when not controlled in the fall or early spring, especially in no-till systems. Winter annual weeds typically emerge from late summer through fall, can overwinter and then flower to set seed in the spring/early summer. Seedling winter annual weeds can be difficult to distinguish from other weeds, particularly if they are in the same family (Table 1). Many fallemerging weeds have a rosette growth stage such as dandelion, horseweed, prickly lettuce, Shepherd’s purse, and other members of the Brassicaceae, making identification more difficult.
Accurately identifying weed species can help determine the right herbicide applications needed to manage the weed species in each field. The University of Missouri publishes several good diagnostic resources that include color photos and keys for identification.1,2,3 Consider accessing Early Spring Weeds of No-till Crop Production, NCR 614 Extension Publication at http://extension.missouri.edu/p/NCR614.
The impact of winter annual weeds in cropping systems is sometimes overlooked because these weeds typically complete most of their life cycle prior to or shortly after corn and soybean planting. Dense mats of winter annual weeds may delay soil warming in spring, compete for water and nutrients, and interfere with crop planting. Winter annual weed species are hosts for some pests (Table 2). Henbit and purple deadnettle are hosts for soybean cyst nematode.
Table 1. Winter annual and similar weed species
|Family Name||Common Names|
|Asteraceae||Marestail, Cornflower, Fleabanes, Prickly lettuce, Dandelionp, Butterweeda|
|Brassicaceae||Bushy wallflower, Field pennycress, Shepherd’s purse, Smallflowered bittercress, Tansy mustard, Virginia pepperweed, Wild mustard, Yellow rocket|
|Caryophyllaceae||Common and Mouseear chickweedp|
|Lamiaceae||Henbit, Purple deadnettle|
|Scrophulariaceae||Corn speedwell, Purselane speedwell, Common mulleinb|
|Liliaceae||Star-of-Bethlehem, Wild garlicp, Wild onionp|
|Poaceae||Annual bluegrass, Carolina foxtail, Downy brome, Foxtail barleyp|
Table 2. Winter annual weed hosts for soybean cyst nematode (SCN) and black cutworm (BCW).
|Soybean Cyst Nematode||Black Cutworm|
|Common chickweed||Common chickweed|
|Shephard’s purse||Shepherd’s purse|
|Small-flowered bittercress||Yellow rocket/Mustards|
|Purple deadnettle||Curly dock|
Winter Annual Weed Identification
Although agronomists may overlook the value of accurate identification of weeds in the fall, proper identification can help focus weed management decision-making. Selecting the right herbicides and proper application timing can influence performance.
Common winter annual weeds in the Midwest include: henbit, marestail, shepherd’s purse, field pennycress, prickly lettuce, and purple deadnettle.4
Purple deadnettle and henbit
Purple deadnettle and henbit are often misidentified due to their similar appearance. The best way to identify these plants is by looking at the leaves in the upper portions of the stem; henbit leaves attach directly to the stem while the upper leaves on purple deadnettle have short petioles that attach leaves to the stem (Figure 1).
Marestail forms a basal rosette after germination and seedlings are covered with coarse hairs (Figure 2). Seedling leaf margins are toothed. Flowers are white to pink with yellow centers. Marestail is more susceptible to herbicide application in the fall compared to early-spring.
Shepherd’s purse and dandelion
To distinguish between Shepherd’s purse and dandelion, examine the lobes in the rosette leaves, if the leaves come to points towards the center of the rosette, it is a dandelion (Figures 3 & 4). Dandelion leaves or stems will exude a milky sap when broken.
Field pennycress and prickly lettuce
Field pennycress and prickly lettuce are in different families but can be misidentified in the seedling stage (Figures 5 & 6).
Common chickweed is an annual, whereas mouseear chickweed is a perennial with a similar growth habit. Common chickweed leaves are bright light-green, nearly rounded with pointed tips, and hairless (Figure 7). Mouseear chickweed leaves are dark green, elongated, and covered with soft hairs. Common chickweed has a single straight row of hairs along the stem.
A fall herbicide application can effectively reduce weed populations from overwintering and help reduce the number of seeds set in the spring. Visit with your Monsanto Crop Protection Representative, local retailer, or visit www.RoundupReadyPLUS.com for solutions and recommendations.
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