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DIFFUSE KNAPWEED
Diffuse knapweed is usually biennial but can also be a short-lived perennial. It reproduces exclusively from seed. It will not tolerate flooding or shade and thrives in the semi-arid West. It is a tough competitor in dry sites and rapidly invades and dominates disturbed areas. The main economic loss caused by this weed is reduction in quality forage, generally in a rangeland situation.
Control
The seed longevity and ability to spread makes Diffuse knapweed difficult to control. The best defense is to halt seed production. Biological: Livestock will consume it early in the spring but are less likely to graze it after the plant reaches the bud stage. There are several insects available. Urophora affinis and U. quadrifasciata can reduce knapweed seed production. Cyphocleonus achates is an effective root weevil, and Sphenoptera jugoslavica adults feed on the leaves, while their larvae mine within the root. Combining several of these insects is proven the most effective.
Herbicide: Herbicides are most effective when applied at the rosette to bolt stage, before the plant flowers. This department has seen good results in rangeland, pastures, and other non-crop areas by applying products containing clopyralid, metsulfuron, picloram, or dicamba. Picloram is a "restricted use" product and can only be applied by a licensed applicator. When choosing any kind of control method, assure that your choice is suited for your particular situation. Always read and follow the entire product label before applying any herbicide.
When choosing any kind of control method, assure that your choice is suited for your particular situation. Always read and follow the entire product label before applying any herbicide. |