Rice growers have two new herbicides to control large barnyardgrass — Clincher and Regiment. These herbicides, developed by Dow AgroSciences and Valent USA Corp., have different biological and utility profiles. As a contract researcher, I have 10 years of experience with Regiment and five years with Clincher.
Clincher is a postemergence grass herbicide with no residual soil activity. It has the same mode of action as Select, Fusilade and Whip. Unlike Whip, Clincher is completely safe to rice. I have tested four times the labeled rates at various rice growth stages with no injury or yield reduction. This attribute makes Clincher unique.
Another unique characteristic is Clincher's ability to kill large barnyardgrass, especially postflood. Most other herbicides in this family are weak on large barnyardgrass. In 2002, many growers used Clincher seven to 10 days after the flood was established and were very pleased with the results.
Clincher is also labeled for preflood application on small one- to four-leaf grass. Like most rice herbicides, preflood applications of Clincher work best when applied with good soil moisture. Having adequate soil moisture is more predictable on silt loams than on clays.
For optimal preflood activity, Clincher should be applied to wet clays. This means applying Clincher immediately after a significant rain or flush. Clays can lose surface moisture very quickly. With low humidity and a north wind, clays can go from sticky wet to checked overnight.
If soil moisture is questionable and Clincher is the product of choice, it may be best to wait to make the application as soon as possible after the flood is established.
This preflood moisture problem on clays in not unique to Clincher — it exists for most rice herbicides, including propanil.
Clincher does not control broadleaf weeds or sedges, and tank-mixes with most broadleaf and sedge herbicides can reduce grass control. A significant amount of research has evaluated grass antagonism. I have looked at preflood and postflood applications and the data is somewhat variable, but most broadleaf herbicides can affect grass control. At present the label recommends mixes with only Facet, Command, and Pendimax (pendimethalin).
Clincher also controls bearded and Amazon sprangletop, broadleaf signalgrass, fall panicum, seedling johnsongrass and propanil/Facet-resistant barnyardgrass. The Clincher SF label calls for 13.5 to 15 ounces per acre and a stout dose of crop oil (1 quart per acre).
The higher Clincher rate is needed for most postflood applications, and at least 50 percent of the grass foliage needs to be exposed for control. In cases where the application can be made one week after flooding, 13.5 ounces will be adequate.
If grass pressure is heavy, good coverage is necessary. This means high water volume (10 gallons per acre) and precise application.
The tank-mix with Command or Facet will have use when applied preflood for controlling emerged grass and providing residual activity. These programs most likely need to be followed by a broadleaf herbicide like Grandstand or Permit.
Regiment has a different mode of action than Clincher, but like Clincher has no soil activity. Regiment is an ALS inhibitor, and, therefore, is slow-acting. Rice tolerance to Regiment is good with some stunting and slight yellowing occurring in some instances.
I have evaluated rice tolerance for many years and have not had yield problems — even at rates well above recommendations. Medium-grain varieties are more sensitive than long-grain varieties.
Regiment is excellent on barnyardgrass with up to four tillers. At growth stages larger than four tillers, Valent only claims suppression. It is labeled as suppression for postflood application on barnyardgrass up to the heading growth stage.
Regiment also controls several broadleaf weeds, including hemp sesbania, northern and Indian jointvetch, smartweeds, dayflower, and ducksalad. Regiment does not control broadleaf signalgrass or sprangletop, but it does control large johnsongrass.
Regiment was used on many rice fields last year with good results. There were some performance problems with barnyardgrass. The vast majority of the problems occurred during a period of cool weather or when the spray volume was less than 10 gallons per acre.
Even though this herbicide was researched for over 15 years, this problem was not discovered until full-scale commercial use. I have to commend the Valent representatives for following up on these complaints and finding the answers. When barnyardgrass is slowed by cool weather, Regiment may not provide the best control and coverage is essential.
Regiment can be tank-mixed with Bolero or Prowl as an early preflood treatment to provide residual grass control or mixed with Grandstand, 2,4-D or Blazer for added broadleaf control when applied postflood.
Propanil is the only herbicide that can reduce grass activity when tank-mixed with Regiment.
An early preflood application of Regiment at 11.25 grams per acre or slightly less plus Prowl followed by a late preflood or early postflood application of Regiment looks promising. Another program that has worked well is Command applied pre-emergence followed by Regiment preflood or early postflood.
Regiment should be applied with a Valent-approved silicon-based adjuvant. The use of crop oil or nonionic surfactants may reduce weed control.
Coverage of weeds at application is very important with Regiment. The label calls for 10 gallons per acre spray volume. Research conducted this year at my Stuttgart, Ark., facility showed the importance of this recommended spray volume. Regiment was applied by air at selected volumes and with various nozzle deflection angles. When Regiment was applied in a spray volume of 6 gallons per acre, barnyardgrass control was 50 percent; at 8 gallons and 10 gallons, control was 80 and 95 percent. This test showed the importance of the recommended spray volume of no less than 10 gallons per acre.
The drift profile of Regiment is good. Grain sorghum is the most sensitive, followed by corn, soybeans and cotton. In simulated drift studies, only grain sorghum failed to recover from a heavy drift rate of 10 percent of the full rate.
In actual aerial drift studies, the results were even better with Regiment. Down-wind deposition went less than 400 feet on sensitive plants.
Last year, both Clincher and Regiment were used for specific reasons. In the future, as rice growers become more familiar with these herbicides, they will be used in sound weed control programs.
Charles Guy, a former weed scientist with the University of Arkansas, provides weed control consulting in southeast Arkansas through G&H Associates.