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Weed Outlook
Fall is an excellent time to control quackgrass with Roundup Ultra. Harvested silage corn and wheat fields are ideal sites for fall quackgrass control. Ideal timing is from early September to mid-October.
Rather than worry about the calendar, it is best to determine if the field meets the following criteria:
- Quackgrass is at least 6 inches tall, green, actively growing and not covered with crop residue (corn stover)
- No visible signs of frost injury on quackgrass leaves (quackgrass can tolerate light frost without damage, so the occurrence of a frost date does not preclude the use of Roundup Ultra later in the fall)
- Minimum daytime high of 50F (60F preferred)
- No risk of rain for at least two hours. I suggest six hours if temperatures are cool.
- Wind less than 10 mph.
The likelihood of meeting all five criteria diminishes as we get later into the fall. Roundup Ultra should be applied at a rate of at least 1 qt./A. Always add ammonium sulfate (AMS) at 17 lbs./100 gal. to the spray solution.
Tank-mixing may reduce Roundup Ultra activity on quackgrass (antagonism) and should be avoided if the target weed is quackgrass. If 2,4-D ester is tank-mixed with Roundup Ultra, it is suggested that the Roundup Ultra rate be increased by 1 pt./A to compensate for possible antagonism. Adding AMS is critical if tank-mixing Roundup Ultra with other herbicides.
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