Cotton growers are in need of the Section 18 exemption because the canceled production of cyanazine products, including Bladex, leaves a shortage of acceptable, economical alternatives for the requested use, according to the label request.
“The short residual for cyanazine provided more opportunity for rotational crop establishment of fall cover crops and/or fall grain crops such as wheat. It is also less restrictive for following year crops such as corn and grain sorghum,” Mississippi’s application says.
“The only fully registered alternatives for cyanazine replacement are diuron, prometryn, clomazone, fluometuron, pendimethalin and norflurazon. Each of these products, which are sold under various trade names, has longer rotational crop intervals of most of the economically important crops in the Mississippi Delta, especially diuron, norflurazon and clomazone.”
Produced by Valent, Valor (flumioxazin) has a shorter residual than any of the alternatives and is only slightly higher in cost than the lowest cost, but longest residual, alternative of diuron, says Charles Ed Snipes of the Delta Research and Extension Center at Stoneville.
While a layby application of Valor costs approximately $10 per acre, cyanazine averages about $7 per acre. At $7.42 per acre, diuron is the most economical alternative, but is also more restrictive, rotationally, than other more costly, but less restrictive products that range in cost from $8.90 per acre (fluometuron) up to $10.58 per acre (prometryn), says Snipes, Extension cotton specialist for the Delta region.
Another reason cotton growers need Valor for the control of cotton weeds at layby, Snipes says, is that pigweed is not easily controlled with the commercial products that are currently available to farmers, with the exception of cyanazine, which is expected to be in short supply.
“Changes in crop production systems for cotton from intensively tilled systems utilizing trifluralin to conservation tillage production systems that cannot utilize trifluralin have resulted in greater acreage being infested with pigweed,” the application to EPA says.
“Since layby applications are fairly late in the season, use of diuron would only allow cotton to be grown the following season.”
Snipes says cotton growers are increasingly more concerned about weed resistance management. “In 1995, pigweed was not listed in the top ten most troublesome weeds in cotton. However, in 2000 it was considered the number one most troublesome weed,” he says.
“This shift is a result of farmers applying pyrithiobac in a pre-emergence treatment followed by a postemergence application over large acreages each year. Pyrithiobac has a very specific site of action in the plant and pigweed has a large gene pool, resulting in a favorable scenario for development of herbicide resistance. Over the past six years of continued use, much of the pigweed in Arkansas has developed resistance to the ALS inhibitor class of herbicides, which includes pyrithiobac.”
The diphenyl ether class of herbicides including flumioxazin provides good control of pigweed and offers good resistance management to the triazines, ureas, and substituted ureas, Snipes says.