This fall most areas are good for fall weed control, but there will also be some areas that it may not be the best.
Fall weed control can give the best weed control but it also can be a poor time. If the noxious weeds were sprayed or clipped earlier this summer and there is good weed growth now, this would be a good time to spray these weeds and get a good kill. However, if the weeds were not controlled early and now are tall, very mature and do not have a lot of regrowth you may not even want to make an effort because it will not do any good.
The questionable area is where the weeds were maybe clipped earlier and there is regrowth or the regrowth is starting to dry up because of the dry conditions and is not growing well. These areas then become questionable to spray. If you want to spray these areas make sure that you use a spray that has residual effect so when the plant starts growing again after a rain, it will be killed then.
Lastly, even though we have not had a freeze we are in September and the perennials have started to prepare for winter by sending nutrients down to the roots to help the plant make it through the cold winter months.
If you have fall spraying for leafy spurge, Canada thistle, sow thistle, wormwood sage, and musk thistle to do now is the time, not when you get busy with harvest in the next few weeks.
Source: Paul O. Johnson, iGrow