Preemergence herbicide programs for corn
* HPPD-inhibitors. Examples of HPPD-inhibitors are isoxaflutole (e.g. Balance Flexx, Corvus, and Prequel) and mesotrione (e.g. Callisto, Lexar EZ, Lumax EZ). These products either contain atrazine or should be applied with atrazine, and are excellent on kochia, pigweeds, velvetleaf, and many other broadleaf weeds. Lexar EZ, Lumax EZ, and Corvus+atrazine will provide the best control of grass weeds. Corvus will also control shattercane. Balance Flexx has activity on shattercane but is less consistent than Corvus. Prequel has a low rate of Balance mixed with Resolve and will not provide the same level of residual weed control as Lexar EZ, Lumax EZ, Balance Flexx, or Corvus used at full rates. Keep in mind, products containing Balance should not be applied to coarse-textured soils when the water table is less than 25 feet below the soil surface. Balance Flexx does not provide adequate control of sunflower. Corvus will be much better than Balance Flexx, provided the sunflower is not ALS resistant. Herbicides containing clopyralid such as Hornet, TripleFlex, or Surestart will provide very good control of sunflower. Zemax is a new herbicide containing S-metolachor and mesotrione, and is similar to Lumax EZ or Lexar EZ less the atrazine. Control of broadleaf weeds with Zemax will be less than Lumax EZ or Lexar EZ unless atrazine is added to the mix. Callisto, a component in Lexar EZ or Lumax EZ, has the same mode of action as Balance Flexx or Corvus but has less activity on grass weeds, thus if applied preemergence it should be applied with an acetamide and atrazine.
* Triazine. Atrazine is a common component of many preplant and preemergence herbicide premixes for corn. Where weed pressure is light, a March application of atrazine with crop-oil concentrate and 2,4-D or dicamba can control winter annual weeds such as mustards and marestail and provide control of most germinating weeds up to planting. If kochia is the key target, 0.5 to 1.0 lb/acre atrazine with a pint of dicamba applied in mid-March can provide excellent control of germinating kochia. It is essential to add glyphosate to the mix if winter annual grasses are present. In a premix with other herbicides, atrazine adds burndown control of newly emerged grasses and broadleaf weeds present near planting time, as well as some residual control of small-seeded broadleaf weeds such as pigweeds and kochia (except for triazine-resistant populations).
* PPO-inhibitors. Examples of PPO-inhibitors include flumioxazin (e.g. Valor, Fierce), and saflufenacil (Sharpen, Verdict). Valor or Fierce must be applied 7 to 30 days before corn planting in a no-till system. These herbicides provide excellent control of pigweeds; however, they are marginal on kochia. Fierce will provide improved control of velvetleaf compared to that from Valor. The addition of atrazine will enhance kochia, pigweed, velvetleaf, and morningglory control, provided the populations are not triazine-resistant. Sharpen and Verdict have excellent activity on pigweeds, kochia, and large seeded broadleaf weeds, however, length of residual is relatively short compared to other preemergence products when all are compared at full rates.