Check the nodes, are they still green - there is still uptake occurring. At hard dough, even with green stems and leaves, the cereals can be safely swathed for grain for quicker dry down and thus harvest. They seem to invade our fields and pastures practically overnight. Members of the sunflower or composite family, thistles produce incredible numbers of light, buoyant seeds which are carried by wind and water, and spread by livestock, wildlife, and agriculture products. They most readily establish in distributed areas, tilled crop fields, and bare or weakly sodded areas in pastures.
Correct identification is the essential first step for any weed control program.
The most common biennial found throughout the country is the Bull thistle. But other regionally important biennial thistles include Musk, Scotch, and Milk thistle. Small infestations of biennial thistles can be controlled with a shovel. Cut them off an inch below ground level to prevent re-sprouting. Notice whether first year rosettes are also present which will become next year's large, bolting seed producers.