Common chickweed, henbit, and purple deadnettle are cool-season weeds we usually see in crop fields during the fall and winter.

However, other weeds, such as dandelions, have become more prevalent in recent years. Dandelions are generally considered a major lawn or pasture weed but are increasingly found in grain crop fields.

The expansion of dandelion populations in field crops is likely due to fewer applications of soil-residual herbicides along with no-till crop production practices.

Dandelions are perennial plants with a taproot that helps it reproduce and survive. In addition, dandelion plants are prolific seed producers. During its peak flowering period in early spring, the flowers quickly transition from yellow blooms to mature seeds. 

Like thistle seeds, dandelion seeds are easily carried and spread by the wind to other sites. No-till crop fields are a prime seedbed.

Dandelions germinate from seed in late summer and early fall producing small rosettes and begin an active growth period in the early-to mid-fall when temperatures start to moderate.
 
Therefore, initiating control during the late fall or early winter months will likely provide the most benefit. Spring control options for dandelions are often less consistent or require higher herbicide rates to be effective. Also, if you wait until spring to initiate control efforts, plants may flower before control is attempted. 

In corn and soybean fields, herbicide options in the fall consist of 2, 4-D; glyphosate; or a combination of both. Other weeds that are present at the time of application may favor the use of one treatment over another. 

Apply herbicides anytime after crop harvest and after dandelions have initiated active growth. Generally, the best time period is through early- to mid-December, provided daytime temperatures reach 55 to 65 degrees Fahrenheit for a couple of days.

In some cases, only spots in the field which are moderately to heavily infested with dandelions will warrant herbicide treatment. If these areas are left untreated, they can result in dandelion populations that may interfere with crop emergence and ultimately reduce crop yields.

Submitted by J.D. Green, Extension Plant and Soil Specialist, University of Kentucky