Weed Science - University of Wisconsin

Dandelion

Jerry Doll and Tim Trower*

Family: Composite (Asteraceae)

Name: Taraxacum officianle

Life Span: Perennial

Description:
Leaves are crowed in a basal rosette, blades are simple and variously lobed. Blades may also be lightly pubescent, especially on the lower surfaces and mid-veins, and contains a milky substance. The most prominent feature is the flower head, which upon first opening contains a series of yellow ligulate flowers borne on a hollow pseudostem.

Reproduction:
Dandelion is generally an apomictic plant and seed production normally occurs without pollination. Seed production varies from 54 to 172 seeds per head and a single plant can produce more than 2000 seeds. One estimate is that more than 240,000,000 seeds/acre could be produced annually by a dense stand of dandelions.

Flowering peaks in early summer with a second flush of flowers from mid-September to early October. Some plants may flower any time during the growing season. Two patterns of flowering are found. In the early spring, flower heads remain open from sunrise to dusk, but in June to August, they close by noon. Unusual weather conditions, such as a sudden drop in temperature or very cloudy conditions, cause flower heads to remain closed. Flower heads open for 2 to 3 days in early spring and mid to late fall and for less than 2 days in the summer. The heads remain closed for 10 days in the early spring and fall, 6 to 7 days in the summer and 20 days in late fall before opening a second time to release seed.

Dandelion seeds are readily disseminated by the wind. The pappus expands and forms a parachute-like structure at right angles to the main axis of the seed when the relative humidity is 77% or less. Wind velocities of only 4 mph or more will keep seed air borne. Dandelion seeds are non-dormant when produced.

Control Methods:
Dandelion is easily controlled by a fall application of 2,4-D or dicamba at 1 pt/A applied alone or as a tank mix prior to the first killing frost. Fall-applied glyphosate can also give acceptable control. Do not make glyphosate applications when the air temperature is below 50 degrees F or if the plant has ceased active growth.

Dandelion control in the spring with glyphosate applied alone is often only fair and is seldom acceptable. Broadcast applications of 2,4-D ester at 1 pt/A provide fair to good dandelion control prior to corn emergence. Broadcast application of a 2,4-D/glyphosate tank mix at 1.0/1.0 pt./A will usually provide increased dandelion control compared to 2,4- D applied alone. Postemergence applications of growth regulator herbicides usually provide acceptable dandelion control in corn. Deep tillage such as moldboard or chisel plowing will weaken the plant by disturbing the taproot and may make chemical applications more effective.

2,4-D ester may be applied prior to soybean planting if a seven-day interval is observed between application and planting. There is a slight risk of soybean injury from preplant 2,4- D applications if the soil remains wet and cool during germination, with lighter soils at greater risk. There are no good postemergence options for dandelion control in soybeans at this time. If possible, control heavy infestations of dandelions in the fall if the field is to be planted to no-till soybeans.

SENCOR and VELPAR are both labeled for dandelion control in established alfalfa. SENCOR must be applied prior to alfalfa green-up and VELPAR must be applied prior to two inches of new alfalfa growth or crop injury may occur. Do not treat stands under stress or less than two years old. SENCOR may cause injury to forage grasses. Do not apply to a mixed legume/grass stand unless significant grass injury is acceptable.

Other Information:
Dandelions have minimal impact on quality forage and are readily consumed by most livestock. However, they are wetter than alfalfa and can delay the drying time of hay. The seeds and plant parts are a food source for many types of wildlife. Dandelion seed was available to pioneers as ornamental flowers and was occasionally used as a planting for sod roofs.

Sources:

World Weeds: Natural Histories and Distribution
Weeds of Nebraska And The Great Plains, Nebraska Department of Agriculture
2000 Pest Management in Wisconsin Field Crops

Please read and follow the manufacturer’s label.

*  Senior Outreach Specialist

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