Irrigation, Prescribed Burning and Fertilization

Irrigation

Although there is no information on using irrigation in management of diffuse knapweed, it may be applied in conjunction with other management tactics, similarly to the management of spotted knapweed. Irrigation can stimulate the germination of seeds thus reducing viable seeds in the soil. When followed by a control treatment such as herbicide application or sheep grazing, populations may be reduced. Irrigation can be used to increase the production of many pasture plant species and increase their competitiveness with diffuse knapweed. If mature, competitive diffuse knapweed plants are controlled using herbicides, sheep grazing, or biological control insects, the competitive pasture plants may suppress establishing seedlings.

Prescribed Burning

Diffuse knapweed rosettes re-sprout from root crowns following fire, including intense wildfire, and fire may stimulate seed release from dormancy in the seed bank. In addition, fire may damage perennial grasses and populations of seed-feeding biological control insects, depending on the timing of the burn. Burning plant litter prior to an herbicide application may increase herbicide contact with re-sprouting plants and improve herbicide efficacy. Prescribed burning should be combined with herbicide management on diffuse knapweed infestations. Wildfire may prepare an infested site for rehabilitation using a combination of herbicide application and perennial grass seeding treatments.

Fertilization

Experimental addition of nitrogen and phosphorous increased the biomass and seed production of diffuse knapweed on the Colorado Front Range prairie. Fertilization on native rangeland will likely favor diffuse knapweed over native plants and is therefore not recommended. On cultivated pastures and hay meadows, nutrient management is important to maintaining the competitiveness of desired perennial grasses over diffuse knapweed. Nutrient management combined with judicious use of herbicides and crop rotation is recommended where diffuse knapweed invades tame pastures and hay meadows.

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Last Modified: 06/02/2008