Cotton producers can now apply insecticides to control lepidopterous pests in the 5 percent refuge in both the embedded and external 95/5 Bt cotton refuge options — but only through the pre-squaring stage of development.
The changes in refuge requirements, which were approved by EPA May 10, came after growers in Louisiana and southeast Texas experienced heavy egg lays by cabbage loopers in seedling cotton.
“Most growers in that area use the 5 percent refuge option, and, based on the refuge requirements, they were not allowed to treat that 5 percent of their acreage for these cabbage loopers,” said Walt Mullins, Bollgard II technical development lead for Monsanto.
“Their concern was that if we don't manage these cabbage loopers there's a risk we would lose the stand in the 5 percent refuge. What that would have meant was that they would have had to replant the refuge, which would have been considerably behind the Bollgard cotton.”
Mullins said cotton specialists in Louisiana, including Ralph Bagwell, Extension entomologist with the LSU AgCenter in Winnsboro, La., decided to ask EPA to change the spraying requirements for the 5 percent refuge.
“Ralph had a conversation with EPA as well as our people at Monsanto,” Mullins told editors attending a Cotton Media Briefing in St. Louis. “Basically, they said let's fix this situation for the future and amend the federal label so that growers can treat these refuge acres, but only through the pre-squaring stage of cotton development.”
The ruling applies to cotton containing the Bollgard, Bollgard II and Widestrike insect control traits. Monsanto developed Bollgard and Bollgard II and Widestrike is a product of Dow AgroSciences.
Growers will be allowed to spray insecticides during the pre-squaring phase because the cotton plant is not considered to be a significant host for the bollworm, tobacco budworm or pink bollworm at this stage, according to Monsanto.
“Therefore, the application of the foliar spray will not impact these insect populations, thus managing the potential for resistance development as originally designed in the stewardship plan,” the company said.
EPA has required growers to plant either 5 or 20 percent of their cotton acres in non-Bt varieties since Monsanto received a registration for Bollgard in 1996. The agency made high levels of compliance with the refuge options a condition for re-registration of Bollgard cotton in 2000 and 2004.
The agency said the refuge guidelines for the 20 percent sprayed refuge option remain unchanged.
“These changes for the 5 percent refuge are supplemental to the 2005 Bollgard and Bollgard II Insect Resistance Management Guide and Technology Guide,” said Mullins. “All other practices in these 2005 guides must be followed.”
Monsanto's introduction of Bollgard II, which contains both the Cry 1Ab and Cry 2Ab genes from Bacillus thuringiensis, is also a part of the Insect Resistance Management plan, said Mullins.
Bollgard II provides improved efficacy against bollworms and expands the control of cotton containing the Bollgard gene to armyworms and loopers, but it also improves the inherent insect resistance management quality for greater durability of the technology.
“One of our objectives since we introduced Bollgard has been to make sure we can preserve the technology,” said Mullins. “A part of the IRM plan from the beginning was to develop a dual gene product that would provide two sites for attacking target insects.”
He said the company's Bollgard Activity Chart has placed bollworms down the list of pests because of the single gene's lower activity in cotton blooms. “As a result, growers have had problems with bollworms and have come to expect to make one bollworm spray in an average year and have seen years with two or three sprays.
“The Bollgard II gene has moved the whole lepidopterous complex to the excellent side on the Bollgard Activity Chart,” he noted.
Mullins was asked if growers should expect to spray Bollgard II for bollworms? “Because we can't anticipate every situation, we're advising growers to scout their Bollgard II, and, if they see larvae-causing damage, spray. Our experience thus far has been that the need to spray Bollgard II for bollworms has been rare.”