Success of mowing to control yellow starthistle depends on timing and plant's branching form

Successful control of yellow starthistle by mowing depends on both proper timing and the plant's form of growth and branching. The branching habit of yellow starthistle is highly variable and is in part dependent on the level of competition with other species for light. Field studies were conducted in five Northern California counties to examine the effects of growth form, timing of mowing and number of mowings on yellow starthistle growth and seed production. Erect, high-branching populations were effectively controlled by a single mowing at early flowering, while sprawling, lowbranching plants were not satisfactorily controlled even by multiple mowings. Mowing should provide an effective tool for yellow starthistle control in an integrated approach with clopyralid treatment, prescribed burning or biological control.