It is that time of the year when musk thistles are out.

"The last two years, there has been an extremely abundant crop because of the dry weather we have had. [Usually], mostly good foliage shades the ground and prevents these thistles from germinating," said John Hobbs, agricultural and rural development specialist with the University of Missouri Extension office. "The last two years, we have had a lot of open space and a lot of these seeds have germinated, creating — especially this year — a big problem with the number of thistles. It is just not one person's problem, if you are a landowner, you probably have thistles."

They are found primarily in pastures, hay meadows, roadsides and waste areas.

"Musk thistles are pale green leaves within stickers on the leaves, it is so 'stickery' that cattle will not eat them," Hobbs said. "They are light green, then some time in May they will bolt or send up that center stalk with the bright pink or reddish flowers and of course it is too late then when you start to see the seed heads. The only thing that you can do is pulling them, cut the seed heads off, pull the plant or at the last resort, at least lay them down with a mower.

Musk thistles usually start flowering in spring and can bloom from seven to nine weeks. Musk thistle flower heads are "powder puff" in shape, in contrast to "saving brush" flower heads of some other thistles.

A musk thistle plant may produce from one to more than 100 heads depending upon soil and growing conditions. The upper one or two heads develop individually on long stems while lower branches may have from two to nine heads per branch. The large terminal head is one and one-half inches or more in diameter, solitary and is usually bent over slightly.

Thistle facts

• Research in Kansas indicates one plant per square foot nearly decreases forage production in half. This results in lower income from grazing areas. Loss in income also results from lower quality hay due to contamination by this noxious weed.

• University of Arkansas research shows that 80 percent of seeds from a thistle are deposited within 55 yards of the original plant. Less than 1 percent blows more than 110 yards from the point of origin. Thistles are prolific. A single plant can produce up to 10,000 good quality seeds. The seeds are 90 percent viable up to two months after they are produced and may retain the ability to germinate for more than a year.

• Texas extension recommends two methods of control — mechanical or use of herbicides. Mechanical methods include mowing and hand cutting. Mowing needs to be done with a rotary mower before the first appearance of pink on the flowers. Mowing at full bloom will prevent seed production. Producers should mow cleanly and closely and repeat as needed for control and cutting should take place between the first appearance of pink and the first appearance of brown on the pappus of the earliest head. This presents a problem there may be plants of varying ages in an area.

• Thistle can be controlled by digging the root at least two inches below ground level and removing all soil from the roots. Pick heads that are beyond the bud stage and burn in a controlled fashion.

• Spraying is an effective way to control thistle outbreaks. Musk thistle plants with flower stalks are more difficult to kill than the rosettes. Rosettes need to be treated when they are actively growing and not under drought stress. This probably means in the fall (late October) or spring (mid-April).

• Another control is biological. Specific natural enemies of musk thistle can aid in regulating the spread of this weed. Such natural enemies include the musk thistle rosette weevil and the musk thistle flower head weevil and a musk thistle rust fungus.