In some cases the feeding levels are resulting in deformed flower heads. Other cases, the heads appear to be blooming adequately with minor deformity of the heads yet . Infestations are heaviest within the border rows, but there are reports of active infestations well into many fields. Fall herbicide applications can provide some of the best perennial weed control of the season. However, fall herbicide applications do not always provide acceptable perennial weed control.
Many factors can influence perennial weed control.
Beverly Durgan, Extension Agronomist-Weed Science, has put together some weed control tips that should be considered in planning fall perennial weed control. Good active growth of the perennial weed is needed. New shoots that have formed from underground rhizome parts will have more active growth than old plant parts that have flowered. Perennial weeds should have between 6-8 inches of new growth before herbicides are applied. After small grain harvest is a good time to apply herbicides.