By Mark Loux
A commonly asked question about fall herbicides – how late in the fall can herbicides be applied and at what point is it too cold to apply? We have applied well into December under some very cold conditions and still obtained effective control of winter annuals. We suggest applying before Thanksgiving and aiming for a stretch of warmer weather if possible, but the effective treatments should work regardless. Extended periods of freezing weather will cause the perennials to shut down – dandelion, thistle, dock.
We received a lot of questions about annual bluegrass this year, especially regarding difficulty in controlling it in the spring. Fall is a good time to control this weed. This will require the addition of glyphosate to whatever herbicide mix is being used.
Wheat fields not treated with burndown herbicides at planting may also be subject to infestation with winter annuals and dandelion. There are several effective postemergence herbicide treatments for wheat that can be applied in November to control these weeds. Fall-applied herbicides can control these weeds (especially dandelion) more effectively than spring-applied, with less risk of crop injury. The most effective postemergence treatments include Huskie, Quelex, or mixtures of dicamba with either Peak, tribenuron (Express etc), or a tribenuron/thifensulfuron premix (Harmony Xtra etc). We discourage application of 2,4-D to emerged wheat in the fall due to the risk of injury and yield reduction.
Source : osu.edu