Weed Control Guide for Ohio Field Crops

Roundup Ready Corn - Postemergence Herbicides

Herbicide	Formulation	Product Rate Range
Roundup Ultra Max	3.75S	20 - 26 oz
Glyfos X-Tra	3S	24 - 32 oz
Touchdown	3S	16 - 32 oz
Glyphomax, Glyphomax Plus	3S	24 - 32 oz
Cornerstone	3S	24 - 32 oz

Tank-mix with: See labels.

• The products shown contain glyphosate, a translocated herbicide that controls emerged annual and perennial grass and broadleaf weeds. Variations in the formulation may result in differences in product rate, adjuvant recommendations, and rainfastness. Additional glyphosate products may be approved for postemergence use on Roundup Ready corn. Users should consult labels and local product use guides for more specific information. Apply postemergence only to corn hybrids designated as Roundup Ready.
• Mode of action: EPSP synthase inhibitor.
• Apply from corn emergence through the 8-collar stage or until corn is 30 inches tall, whichever occurs first.
• The maximum use rate for Roundup Ultra Max in one application is 26 oz/A. Sequential applications are allowed, but the maximum use rate allowed per year (total of postemergence plus harvest aid applications) is 52 ounces/A.
• The maximum use rate for Glyfos X-Tra, Glyphomax, Cornerstone, Touchdown and most other glyphosate products in one application is 32 oz/A. Sequential applications are allowed, but the maximum use rate allowed per year (total of postemergence plus harvest aid applications) is 64 ounces/A.
• OSU research shows that a single postemergence application of glyphosate is not likely to provide adequate weed control except where weed populations are extremely low. One of the following strategies is recommended for consistent control: 1) application of a preplant or preemergence herbicide (at approximately half the labeled rate) prior to postemergence glyphosate application, or 2) early postemergence application of glyphosate in a tank-mix with herbicides that provide residual control (atrazine, Harness Xtra, Bicep, etc). Maximum height of corn at the time of application varies with the tank-mix partner.
• Velvetleaf is most easily controlled when less than 4 inches tall and actively growing. Large velvetleaf can be difficult to control with glyphosate, especially when drought-stressed. The addition of ammonium sulfate (8.5 to 17 lbs/100 gallons) will improve control of velvetleaf and some other weeds. Ammonium sulfate will also improve control when using hard water, when daytime air temperatures are 55 degrees or less, and when tank-mixing with Bullet, Micro-tech, or Partner.
• Annual morningglory, groundcherry, ladysthumb, and Pennsylvania smartweed are more difficult to control than other annual weeds, and glyphosate should be applied when weeds are less than 6 inches tall for best results.
• Control of perennial weeds will require higher rates than annual weeds. Application when perennials are in the bud to bloom stage (or boot to seedhead for grasses) will provide the most complete control of the entire plant. Minimum size of various perennial weeds for most effective control through the growing season: quackgrass, Canada thistle, wirestem muhly, and yellow nutsedge - 6 inches; field bindweed and common milkweed -12 inches; johnsongrass and hemp dogbane - 18 inches.
• Apply in a spray volume of 5 to 20 gpa. Using a volume of 15 to 20 gpa, selecting the appropriate nozzles, and reducing spray pressure will reduce the potential for spray drift. Take precautions to reduce spray drift, since corn, soybeans, and other sensitive crops are likely to be growing in areas surrounding treated fields.

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