Necessary control of noxious weeds

The Kansas Noxious Weed law requires the control and eradication of 14 plants designated as noxious weeds by Kansas legislature.

This law became effective in 1937 and lists specific duties for landowners, the county and state. Landowners are charged with control of all noxious weeds on their property.

Of the 14, I will briefly discuss three of the weeds we commonly see in Southeast Kansas.

Sericea lespedeza has become the most serious weed problem in Kansas grazing lands. Sericea lespedeza occurs primarily in the eastern third of Kansas, but has invaded numerous CRP stands in central and western Kansas.

Mowing in mid-to-late July will eventually reduce stands of sericea lespedeza to some extent; but even after several years, stands will not be eliminated.

Herbicides applied at the correct time and under favorable environmental conditions can significantly reduce sericea lespedeza. While Remedy and PastureGard work well when applied in June or July. Escort XP is recommended when applied in the fall.

The tremendous seed bank Sericea produces helps to reestablish stands. Therefore herbicide treatments will need to be repeated every two to four years to keep this species in check. Initial treatments should reduce dense stands to the point where spot treatment can be used in future years.

For complete details on sericea lespedeza and its control, see "Sericea Lespedeza: History, Characteristics and Identification," K-State publication MF-2408.

Musk thistle was first introduced into the United States in 1852 in Pennsylvania; it now occurs throughout most of the country and is found in nearly all 105 Kansas counties. Musk thistle was first reported in Kansas in 1932 and declared a noxious weed in 1963.

The goal of any control practice should be to prevent seed production. The first line of defense against musk thistle invasion on range and pasture is good grazing management. Use stocking rates designed to avoid overgrazing; this maintains a competitive cover and prevents bare ground.

Prescribed burning in the late spring will not directly kill musk thistle, but does stimulate the warm season grasses that help prevent musk thistle from becoming established.

Scattered plants of musk thistle can be effectively controlled by hand cutting and digging. Flowering heads should be removed and placed in a tight container and either buried or allowed to rot to prevent possible seed germination.

Mowing can be an effective control of musk thistle if done when the plants are in the late-bloom stage. Repeated mowing is generally necessary to eliminate seed production and control musk thistle.

A number of herbicides are labeled and effective for control of musk thistle. These include 2,4-D, dicamba, picloram and metsulfuron methyl. Chemical control of musk thistle declines after the plant bolts and begins to flower.

Treatment of musk thistle rosettes in the all or spring with recommended herbicides typically results in 90 to 100 percent control.

Johnsongrass was introduced into the United States as a forage crop. It spreads by seed and rhizomes making control at young stages important. A single plant can produce over 80,000 seeds in one growing season and 275 feet of rhizomes. The seeds can remain viable for 10 years.

The control plan for johnsongrass should include preventing rhizomes, weakening or killing the plant, preventing seed production, controlling seedlings from shattered seed and fall tillage to bring the rhizomes to the top to be killed by winter weather.

Johnsongrass responds to tillage like most tough perennial weeds. Intensive tillage will suppress rhizome Johnsongrass while moderate tillage will break and spread rhizomes and allow Johnsongrass to thrive.

Intensive grazing and mowing can be used to reduce a stand of Johnsongrass. If grazed or mowed closely for at least two years, the plants become weak and stunted and the rhizomes become concentrated near the soil surface.

A selective herbicide, like Roundup, can be used with a ropewick applicator or by spot spraying.

Specific recommendations for noxious weeds can be found in the annual issue of Chemical Weed Control for Field Crops, Pastures, Rangeland and Noncropland available from Kansas State University.

All chemicals must be applied according to label directions. Brand names are for product identification only, no endorsement is intended nor criticism implied of similar products not mentioned.

County noxious weed departments are also available to assist you.

More information can be found at the Kansas Department of Agriculture's Noxious Weed site at http://www.ksda.gov/plant_protection/content/349.

Other weeds labeled as noxious are bur ragweed, Canada thistle, hoary cress, kudzu, leafy spurge, pignut, quackgrass, Russian knapweed and field bindweed. Bull thistle and multiflora rose are county option noxious weeds.