Herbicides Used Pre- and Postemergence to Weeds

2,4-D (Amine 4): PHI 45d, REI 28h, Group 4.   Can make one preplant or preemergence application per crop cycle. Apply up to 2.14 pt/A (1.0 lb ae/acre) to soil anytime after planting but before corn emerges. Can make one postemergence application per crop cycle. Apply a maximum of 1.07 pt /A (0.5 lb ae/acre) per application. Use drop nozzles to direct spray toward base if corn is over 8" tall. Do not apply from 7 to 10 days before tasseling to dough stage. Allow a minimum of 21 days between applications. Use a maximum of 3.2 pts/acre (1.5 lbs ae/acre) per year. Reduce rate of 2,4-D if temperature is hot and soil is wet. Use only the amine formulation of 2,4-D; Do not use any ester or low-volatile ester formulations. Use all precautions to avoid spray drift to desirable broadleaf crops.

atrazine (Aatrex 4L): REI 12h, Group 5.  Apply preplant incorporated or to the soil surface immediately after planting. Use alone only if annual grasses are not a problem.  Shallow cultivation may help to control annual broadleaf weeds. May be tank mixed with any of the preemergence grass herbicides listed above as well either glyphosate or paraquat for burndown of existing weeds.

For postemergence applications, add either 1 qt/A of crop oil concentrate or 1 gal/A of spray oil. Apply when weeds are 1 to 1 1/2" high and before corn is 12" high. This treatment can be used as the primary broadleaf herbicide treatment instead of an application at planting or it can be used as an emergency treatment if the soil-applied broadleaf herbicide treatment failed. If applied correctly, this application will control the emerged weeds and will continue to provide residual control for later-emerging broadleaf weeds. Check label for additional precautions regarding the use of crop oil and petroleum oils.

Only 1 lb active ingredient of atrazine is recommended for sweet corn in New England. This is well below the rate on the label and constitutes best management practices for groundwater protection. This rate could be reduced further, although the grower should be prepared to make a second application of atrazine if any weeds escape.

halosulfuron (Sandea): PHI 30d, REI 12h, Group 2.  Apply 2/3 to 1 oz/A over the top or with drop nozzles from the spike through layby stage of the corn.  If necessary, a sequential treatment of this product at 2/3 oz/A acre may be applied only with drop nozzles semi-directed or directed to avoid application into the corn plant whorl.  Do not apply more than 2 applications per year.  Do not use on “Jubilee” sweet corn.  Other varieties may also be sensitive to injury.  The use of non-ionic surfactant is recommended for use on emerged weeds (1 to 2 qt/100 gal spray). Works on germinating broadleaf weed seeds, and also on emerged broadleaf weeds.  Control varies with type and size of weed.  Species listed on the label include redroot pigweed, pokeweed, common ragweed, Pennsylvania smartweed, common sunflower, velvetleaf, wild mustard, yellow nutsedge, and wild radish. Do not cultivate for 7 days after application.

mesotrione (Callisto): PHI 45d, REI 12h,  Group 28.  May be applied by ground for preemergence or postemergence weed control.  See label for list of susceptible species. Callisto provides excellent control of many problem broadleaf species such a velvetleaf and triazine-resistant lambsquarters.  Callisto provides only partial control of yellow nutsedge and no control of ragweed when applied postemergence.

Make a single preemergence application of 6.0-7.7 oz/A after seeding to the soil surface. Can be tank mixed with many other herbicides, and it also included in some premixed products.  See label for details. Use 5 to 6 oz/A if tank mixing with atrazine. In a tank mix, the atrazine rate can be reduced to 0.5 to 1 pt/A.  A grass herbicide must also be used. On cool soils in the spring, Callisto may be a better option than using Prowl to control these two weed species. Callisto does not provide preemergence control of yellow nutsedge. With this weed, it is important to continue to use atrazine (alone or in combination with Callisto) as well as either Dual, Outlook, or Zidua preemergence. See the label for precautions and more information on tank mixes, rates, and weeds controlled.

For postemergence weed control, apply 3 oz/A to corn up to 30" tall when weeds are no more than 3" tall.  Include a nonionic surfactant.  Do not make more than 2 applications per season to corn and do not exceed a total of 7.7 oz/A of Callisto. Applications should be a minimum of 14 days apart.  Use other options if these weeds are present. See the label for precautions and more information on tank mixes, rates, and weeds controlled.  Severe corn injury resulting in yield loss may occur if any organophosphate or carbamate insecticide is applied foliar postemergence within 7 days before or 7 days after Callisto application.  May cause crop bleaching in some yellow popcorn and sweet corn hybrids. Crop bleaching is typically transitory and has no effect on final yield or quality.