Three relatively new corn herbicides, Callisto, Impact and Laudis, all from the hydroxyphenyl pyruvate dioxygenase (HPPD)-inhibiting family of chemistry offer growers some highly efficient options for managing corn weeds and grasses and at the same time help reduce herbicide resistance problems.

Virginia Tech University Weed Scientist Scott Hagood, speaking at the recent Virginia Ag Expo, stressed to growers that glyphosate resistant pigweed and marestail and resistance to a number of acetolactate synthase (ALS)-inhibiting herbicides are all showing up more and more in corn, peanuts, cotton and soybeans in Virginia.

Broadleaf weeds, such as Palmer amaranth and marestail, have evolved resistance to many different classes of herbicides, with some biotypes having "multiple resistance", meaning resistance to more than one class of herbicides in the same plant.

HPPD-inhibiting herbicides such as Callisto, Impact and Laudis generally provide excellent control of these problem broadleaf weeds. Inhibition of the HPPD enzyme leads to the depletion of protective pigments in plant tissue, resulting in bleaching of young tissue which leaves the plant vulnerable to damage by light. HPPD-inhibiting herbicides are relatively new, and because their use has been common only in the past few years, weed resistance to HPPD inhibitors has not yet developed.

Taking advantage of the newer HPPD-inhibiting herbicides provides an efficient way to control weeds and grasses in corn and at the same time fits well into herbicide resistance management programs in crops that are rotated into corn fields.

Callisto is a bleaching type herbicide, comprised of the active ingredient, mesotrione, which is a naturally-derived compound produced by a plant called Callistemon. Mesotrione inhibits the building of a yellow plant carotenoid (pigment) which functions as a sun-screen to protect a plant's chlorophyll.

Laudis is a new systemic herbicide that provides postemergence control of grass and broadleaf weeds in all corn including weeds resistant to glyphosate and other chemical classes. Laudis delivers crop safety and rotation flexibility to soybeans and many other common rotation crops.

Impact is a broad spectrum, systemic, low use rate postemergence herbicide for selective control of broadleaf weeds and grasses in field corn, seed corn, sweet corn and popcorn.

Impact herbicide will provide postemergence control of major broadleaf weeds most common in corn such as velvetleaf, cocklebur, pigweed, waterhemp, lambsquarters and ragweed. Several of the biotypes controlled by Impact have shown resistance to either triazine or ALS-inhibiting herbicides.

Impact also has a high level of activity against several grass species, including giant foxtail, the most common grass problem in corn.

Hagood points out that some of these herbicides control the same weeds and grasses, while some of them have better activity on different weeds and grasses. The key, he stresses, is matching these new herbicides to the problems that occur in corn. Mixing and matching herbicides can save money and provide better control, he notes.

All three products have Canada thistle, large crabgrass, smartweed, lambsquarters, ragweed, jimsonweed, pigweed, chickweed, cocklebur, nightshade, teaweed and broadleaf signalgrass on their label, Hagood says. “In addition, Collisto has done a real good job pre-mergence in a tank-mix with Lumax in controlling resistant weeds. Or, as a postemergence treatment, it has horsenettle control.”

Lumax is a pre-emergence weed control solution in corn, which has long-lasting residual control of a number of weeds. It is an excellent fit for both conventional and glyphosate-tolerant corn acres.

Laudis provides some additional grass control that is not covered by Callisto.

Impact has shown good control of all three foxtails, fall panicum, barnyardgrass, smooth crabgrass and seedling johnsongrass. It has better postemergence grass control relative to Callisto and Laudis, Hagood says

“These are all good products, and I can’t say one is better than the other in broadleaf or Canada thistle control. However, the newest of these products, Impact, does appear to have a broader spectrum of grass control,” he adds.

The Virginia weed specialist says that approximately two-thirds of the corn grown in the state is Roundup Ready varieties. That is a lot of dependence on glyphosate, but it is still the best way to deal with broad spectrum perennials.

He also notes that more and more Virginia corn farmers are going to no-till systems. The key, he says, is to know for sure that you have adequate burndown.

“Most growers are using Gramoxone, but we need to add a triazine-based program to insure the previous crop is burned down and stays down,” Hagood says. He adds that there is an increasing number of triazine resistant weeds, especially in southern Virginia, and growers need to be sure they are not adding to, rather than taking care of residual weed problems by using atrazine on resistant weeds and grasses.

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