Scientific name: Centaurea maculosa

Common name: Spotted Knapweed Updated 07/2002

A. PRIORITY #3

B. DESCRIPTION Spotted knapweed is native to central Europe, where it is found in light, porous, fertile, well-drained and often calcareous soils in warm areas. It occupies dry meadows, pastureland, stony hills, roadsides, and the sandy or gravelly floodplains of streams and rivers. Spotted knapweed tolerates dry conditions, but survives in higher moisture areas as well. Spotted and diffuse knapweed infestations often occur together. Spotted knapweed is a short-lived, non-creeping perennial that reproduces from seed and forms a new shoot each year from a taproot. The weed produces one or more shoots that are branched and 1 to 3 feet tall. Rosette leaves can be 6 inches long and deeply lobed. Leaves become smaller toward the top of the shoot and have smooth margins. Lavender to purple flowers are solitary on shoot tips. Involucre bracts are stiff and black-tipped. The tip and upper bract margin have a soft, spine-like fringe and the center spine shorter than others.

C. CURRENT DISTRIBUTION ON THE SITE SEE APPENDIX 2, MAP #4
D. DAMAGE & THREATS If allowed to proliferate, spotted knapweed infestations spread rapidly. For example, it was first observed in one county in Montana in the 1920’s, but is now found in all Montana counties. Today, over 4.7 million acres are infested. E. GOALS The major goal the MNWAG wants to accomplish is to lessen the economic impact caused by spotted knapweed by eradicating small stands and reducing, then controlling, larger stands.

F. OBJECTIVES (Measurable) (Establish measurable objectives for the planned control activities. Include:

1. the impact on numbers, density, cover, etc. that you want to achieve;

2. the size of the area in which you hope to achieve this;

3. the period in which you hope to achieve it. For example you may state your objectives in terms of reducing percent cover of the species by 50% over an area of 5 acres within 3 years. Another possible objective would be eliminating the species from the site within 2 years.)

G. MANAGEMENT OPTIONS Viable control options are:

(1) CHEMICAL – Research conducted at Colorado State University indicates that dicamba (Vanquish/Clarity) and picloram (Tordon) control knapweed but the weed will reinvade the area unless other management techniques are used.

(2)CULTURAL – If desirable grass competition is evident in knapweed stands, judicious herbicide application that does not injure grasses may allow them to compete effectively with the weeds. Irrigation (where possible) may help stimulate grass competition in these cases. However, rangeland or pastures often are degraded, allowing knapweed encroachment, and herbicides alone will not restore the land to a productive state. Seeding suitable perennial grasses is necessary to prevent weed reinvasion.

(3) BIOLOGICAL – Several insects are available. The seed-head flies Urophora affinis and U. quadrifasciata have been released in Colorado. These insects cause plants to produce fewer viable seeds and abort terminal or lateral flowers. Root-feeding insects may have a more detrimental effect on knapweed populations than seed-feeding ones. Larvae of the yellow-winged knapweed moth feed in the roots. Livestock (sheep, goats, cattle) will eat knapweed. Recent research completed by Colorado State shows that cattle grazing knapweed twice in spring decreased seed set by 50 percent and tumbling off-site over winter by 15 percent. Cattle were managed to achieve 50 percent utilization of pasture and were allowed to graze at two 10-day intervals when diffuse knapweed was bolting and about 6 to 12 inches tall.

H. ACTIONS PLANNED (Treatments and monitoring) (Briefly describe the locations to be treated, materials and methods to be used, and an approximate schedule for control and monitoring activities. If several methods are to be tested, outline the design of the planned experiment or demonstration.)

I. HOW ACTIONS WILL BE EVALUATED (Criteria for success) SEE APPENDIX 4: Examples of data collection forms. J. RESOURCE NEEDS SEE APPENDIX 3: Weed Management Plan Tables

K. RESULTS OF EVALUATION (This section is to be filled in later, preferably within 1 year, when monitoring data has been taken and evaluated, at least preliminarily. The evaluation should be used to determine whether any of the sections B-K above should be modified.)