Command herbicide has made life easier for Mid-South rice producers, but its weakness on smartweed and most black-seeded broadleaves, including hemp sesbania, can lead to control problems with those weeds.
In fact, this past season Arkansas and Mississippi rice fields had tremendous infestations of smartweed. “Over the years, more and more smartweed is going to seed,” said Larry Walton, product technology specialist for Dow AgroSciences. “It seems to be getting progressively worse. It favors very moist conditions.”
Walton said during a Dow AgroSciences plot tour that growers who use Command have a number of alternatives to address the problem.
This includes a new product, Grasp (penoxsulum), which is expected to receive a full label approval for the 2005 season. “Grasp provides excellent postemerge activity and up to three weeks residual on smartweed. The product has controlled smartweed up to 12 inches tall,” Walton said.
Walton suggests that growers in a Command system allow the weed spectrum to dictate which options to go with. Here's what the test plot, located in Humphrey, Ark., indicated:
Command at 0.23 pound per acre followed by Grandstand at two-thirds of a pint plus Permit at 1 ounce “did a pretty effective job on smartweed and black-seeded broadleaves, “but left some crabgrass, barnyardgrass and sprangletop.”
The same rate of Command followed by Grasp at 2 ounces also controlled escaped smartweed, barnyardgrass and black-seeded broadleaves, but not crabgrass and sprangletop, noted Walton.
Clincher applied post-flood at 15 ounces per acre following any of these two applications should allow the producer to clean up escaped grasses, according to Walton. Also, Command at 0.3 pound tank-mixed with 10 ounces of Clincher applied early post and followed by 2 ounces of Grasp plus a third of a pint of Grandstand “is an excellent program for your broadleaves and annual grasses.”
Walton stressed that, “Grasp only has suppression on yellow nutsedge. With a perennial sedge, we recommend tank-mixing with Permit.”
Clincher at 15 ounces and Grasp at 2 ounces controlled sprangletop and barnyardgrass, as well as smartweed and hemp sesbania, noted Walton. “When you put the two together, we're not seeing any antagonism, except with broadleaf signalgrass. We recommend this tank-mix in fields where a grower does not have broadleaf signalgrass.”
Dow AgroSciences recommends that Clincher be applied when soil is tacky or soupy, and this goes for Clincher used in a tank mix with Grasp as well. “We don't recommend putting it out on a dry soil, then coming in and flushing to try and make it work.”
If there is broadleaf signalgrass in the field, another option is a sequential application — apply Grasp at 2 ounces pre-flood for broadleaf weed control, then apply 15 ounces of Clincher one week after flooding, according to Walton.
Grasp tank-mixed with Permit controlled perennial sedge in the study. Grasp and Clincher are both weak on this weed. “Dow AgroSciences does not recommend tank-mixing Clincher with Permit, but will recommend tank-mixes of Clincher, Grasp and Permit. But again, you have to have to have a tacky or soupy soil. Don't try to put it on a dry soil and flush it in.”
Grasp also provides up to three weeks of residual on select rice weeds, according to Walton. “The farmer not only has postemergence barnyardgrass and smartweed control, but if you get a rain or flush shortly afterward, you get residual, too.”
Another option in a Command program is a tank mix of Grasp and Permit 20 to 30 days after planting to clean up black-seeded broadleaves and smartweed, followed by Clincher a week after permanent flood for late-emerging sprangletop or broadleaf signalgrass.
If rain prevents a pre-emerge application of Command, and a 24-C registration is granted for a Command tank mix, a tank mix of 13 ounces of Command and 10 ounces of Clincher and crop oil, early post, at one- to three-leaf grass, can be a solid treatment, according to Walton. In the study, the treatment was followed by a postemergence application of a third of a pint of Grandstand plus 2 ounces of Grasp. “Grandstand provides excellent control of morningglory, one of Grasp's weaknesses,” Walton said.
An advantage to the early 10-ounce Clincher application “is that you can come back with a sequential application of another 15 ounces later if needed post flood and still be within the 25-ounce seasonal maximum,” Walton said.
Walton noted that Grasp will not be recommended for post flood weed control at this time. “We want to gather a little more data in 2005. But initial results demonstrate that it will have an excellent fit.”
Other plots confirmed that Grasp and Clincher tank-mixed did not antagonize Clincher's control of sprangletop.
Grasp, according to Walton, also has a fit in the water-seeded rice market “where there is alligator weed, barnyardgrass, hemp sesbania, jointvetch, duck salad, red stem and annual sedges, you can use it from one-leaf rice to 60 days prior to harvest.”