It used to be that weed control in rice was fairly straightforward — you started spraying propanil when the barnyardgrass emerged and kept on spraying until the weeds were gone or you ran out of money.
With the registration of Command in rice, farmers began changing that approach, applying Command pre-emergence to reduce grass competition with seedling rice while creating opportunities for the use of other herbicide combinations.
“Before, farmers relied on propanil for grass control,” says Bob Montgomery, agronomic research manager for Monsanto's southern region. “Now, we're seeing a different spectrum of weeds, that includes more broadleaf weeds in rice. Permit and propanil combinations work well on grasses and broadleafs that escape the Command treatment.”
Permit, or halosulfuron, is another relative newcomer to rice having first been registered for control of broadleaf weeds and nutsedge species in corn, grain sorghum and turf in the mid-1990s.
After university researchers verified that rice was tolerant of Permit, Monsanto sought registration for the product on yellow and purple nutsedge in 1999. Recently, EPA granted Monsanto a Section 2(ee) registration for tank mixing Permit with propanil on several broadleaf weeds in rice.
“With the herbicides we had earlier, you were looking for broadleaf weed control and hoped to pick up some nutsedge activity,” said Jeff Reeves, farm service manager for Monsanto. “With Permit, you get nutsedge control and also pick up a number of broadleaf weeds.”
“The bottom line is that Permit is a very broad-spectrum herbicide when used in a tank mix with propanil-based products,” says Jay Coker, a rice grower and consultant in Stuttgart, Ark.
“Besides providing superior control of nutsedge, Permit provides good control of black-seeded broadleaf weeds, including smartweed, morningglory, dayflower, hemp sesbania, northern jointvetch and eclipta that are a problem for us in rice. In most instances, these weeds would not be controlled by propanil alone.”
Permit may be applied before or after rice emergence at use rates from 2/3 to 1-1/3 ounces per acre. While the 2/3-ounce rate provides good nutsedge control, a 1-ounce rate appears to provide better broadleaf weed control. Growers may not apply more than 1-1/3 ounces per acre per season.
The label allows growers to apply Permit up to just prior to establishment of the flood but not in the floodwater.
“Besides doing an excellent job on nutsedge and having good activity on broadleafs,” Permit also gives me much more flexibility,” says Larry Ramthun of Valley View Agri in Craighead County, Ark.
“I can apply Permit early postemergence weeks before flooding, or I can put it out right before flooding. I don't have to worry about flooding my fields to activate Permit or keep it activated.”
Farmers may also split applications of Permit, applying 2/3 ounce per acre early and following it with 2/3 ounce prior to flooding if they have a second flush of weeds, says Montgomery.
“With the 2(ee) registration, farmers can vary the rate in a tank mix with a propanil-based product, depending on the size of the weeds,” he said. “That is, they can apply 2/3 of an ounce when the weeds are small or the higher use rate when the weeds are getting on up there.”
How tall? There are reports of growers allowing nutsedge to grow to 6 to 12 inches so they could control multiple flushes of the weeds. By tank mixing Permit with propanil, growers can now take out those weeds along with annual grasses that escape the Command treatment.
Permit also appears to be a good fit for no-till rice, says Reeves.
“In the past, farmers have seen a number of escapes and newly emerged weeds following burndown treatments,” he said. “That has been a limiting factor in no-till rice. By tank-mixing Permit with Roundup Ultra or Roundup UltraMax, you reduce those escapes.”
Reeves said interest has been growing in no-till rice. “We received a lot of questions about no-till at our grower meetings last winter,” he noted. “Permit is one answer to taking problem weeds out of a no-till rice system.”