Tips for identifying fall emerging weeds
As the 2013 corn and soybean harvest begins to wind down, the University of Nebraska would like to encourage growers to take a proactive approach to managing winter annual weeds prior to the onset of winter. Winter annual weeds typically emerge in late summer and fall, survive throughout the winter, and produce seeds during late spring or early summer the following year. Fall control can prevent potential yield reductions associated with delaying removal until corn or soybean planting the following year.
With recent precipitation, many winter weeds are actively emerging. These weeds require undisturbed soils from fall through early summer of the following year to complete their life cycle, and no-till soil management favors this environment. The most common winter weeds in Nebraska are: henbit, marestail, field pennycress, downy brome, dandelion, shepherd’s-purse, tansy mustard, and prickly lettuce. In addition, little barley, evening primrose, and field pansy have been observed in many fields. The first step in effective weed management is being able to accurately identify the weeds.
Henbit is a winter annual (sometimes biennial) herb found in cultivated areas, field, roadsides, or lawns.
Flowering period: March-May
Distinguishing features: The plant is 4 to 12 inches tall having squared green-stem (often becoming purplish in later stage) and reddish purple to pink flowers. The leaves are opposite, clasping the stem in the top portion and leaf-margins are crenate and lobed. The whole plant is sparsely covered with fine hairs. Stem branches frequently root from the nodes. The foliage and stems of henbit are aromatic.
Seedling characteristics: It has a 3-12 mm long, oval-shaped cotyledon with a smooth surface. The petiole is green or purplish and has spreading hair.
Marestail, also known as horseweed, is an annual weed that has a winter or summer annual life cycle. They usually germinate in fall but can germinate in mid-summer when conditions are favorable. Plenty of marestail can be found in no-till fields as well as in cultivated areas, pastures, and roadsides. Marestail contains volatile oils, tannic acid, and gallic acid that may cause skin and mucosal irritation in humans and livestock. Glyphosate-resistant marestail has been confirmed in Nebraska. This is a serious issue and growers should be on the lookout for possible occurrences this fall.
Flowering period: June-September
Distinguishing features: This is an erect herb that has coarsely hirsute stem and leaf surfaces and can be 1.5 to 6 feet tall. It tends to be unbranched unless the plant has been damaged by herbicides or mowing, but it may have branching at inflorescence. Leaves are alternate and crowded on the stem. Flowers are white to pink (ray florets) with yellow centers (disk florets). After fall germination it forms a rosette-like structure. (The larger the rosette is in the fall, the greater its chances of surviving through winter.) Depending on growing conditions, the survival rate of fall-emerged marestail is 14%-84% of total germinated weeds.
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