Imperfection — however slight it may be — can sometimes be a good thing. For example, new Bollgard II cotton varieties, which contain an additional Bt protein for control of lepidopteran pests, performed exceptionally well in large commercial-size fields in 2003, according to reports from the field.
But a few growers and consultants observed the presence of large larvae and a low level of boll damage in several Bollgard II fields. The fields represented less than 1 percent of the commercial fields planted to Bollgard II, according to Monsanto, which developed the technology. All of the fields were in the Mid-South.
While concerning, these problems should help remind growers and consultants who plant Bollgard II in 2004 that you shouldn't just plant it and walk away, expecting it to control 100 percent of the worms 100 percent of the time, noted Walt Mullins, technical manager for Monsanto, which developed Bollgard II. “While we anticipate that the great majority of growers will never need to treat their Bollgard II for any worm species, we recognize that a few may encounter situations where a spray application may be beneficial.
“A lot of university researchers have never seen larvae surviving in Bollgard II,” Mullins added. “There are a few places in the country where we have seen larvae making it through on a small level. It has to be understood that this is possible. There is going to be a learning curve. Our learning now is going to come from our commercial field experiences.”
Cotton varieties containing Bollgard II were planted on about 20,000 acres in the United States this year, with the majority of the acreage going in the Mid-South. Seed companies expect to have enough seed to plant between 500,000 acres and 1 million acres of Bollgard II in 2004.
At the time of this writing, yield data for Bollgard II cotton varieties were incomplete. The following comments regarding Bollgard II performance under moderate to heavy insect pressure were gathered from growers and consultants in August and September 2003:
According to Barry Turner, a cotton producer and consultant from Mer Rouge, La., the technology performed well under heavy bollworm and budworm pressure in 2003. He did not spray his Bollgard II fields for lepidopteran pests all season, while Bollgard fields were sprayed three to four times and conventional cotton five to six times.
In three years of testing, Turner has not sprayed Bollgard II, which included heavy infestations of armyworms and loopers in 2002.
“Based on my limited experience with the Bollgard II technology, it appears to keep bollworms under economic thresholds,” he said.
Jimmy Grant, a consultant with Grant's Agri-Consultant Service, in Flora, Miss., did not find worms over three days old in Bollgard II cotton in 2003. “Despite heavy worm pressure, we're not seeing any feeding damage or scarred-up bolls. We had 60 percent egg lays in Bollgard II cotton but we didn't have to spray it.”
Bruce Craft, a producer from Flora, Miss., is looking for Bollgard II to eliminate the one or two insecticide sprays he now makes on Bollgard cotton. “We were able to accomplish that objective this year. We had lots of eggs but no worms. I also like the extra insurance that Bollgard II offers against armyworms and loopers. I feel like I don't have to worry about worm pests anymore.”
It's hard not to pull the trigger on an insecticide application at 60 percent egg counts, noted David Reed, a consultant with Reed Ag Entomology, Inc., Greenwood, Miss. But the consultant held off on spraying Bollgard II, while treating Bollgard an average of two times and conventional cotton four times for worms.
“We didn't see any worm damage in Bollgard II. You can see to the row the differences between Bollgard II, Bollgard and conventional cotton. There are many more beneficial insects working for you in Bollgard II cotton because you're not spraying it.”
Crawfordsville Ark., consultant Chuck Farr said Bollgard II “performed to expectations this year. We did not have to treat any Bollgard II for lepidopteran pests in 2003, despite the fact that we had moderate to heavy pressure from budworms, bollworms and fall armyworms. I was very impressed. I'm telling my customers to plant at least one field to Bollgard II in 2004. The incremental cost of Bollgard II is money well spent.
“I'm not sure that we will never have to treat Bollgard II,” Farr added. “But what I've seen under heavy pressure looks great.”
In some of the situations where large larvae were found in blooms of Bollgard II cotton in 2003, consultants felt that a spray was necessary, Mullins said. “I can understand their nervousness because they were seeing some larvae in the blooms and they could find some boll damage.
“Any time that we're looking at a biological system to control another biological system, be aware that there are a lot of interactions that occur. It wouldn't be wise to plant Bollgard II and forget about worms until we get a lot more experience growing it under a variety of conditions.”
Clarksdale, Miss., cotton producer Cliff Heaton sprayed his Bollgard II cotton twice for heavy infestations of fall armyworms in mid-August. “I don't know how much damage they did if they did any. We had a couple of fields where bollworm counts were a little high and my entomologist was a little concerned. But I don't think any of them got through the system.
“But it does concern me that we had the fall armyworm problem in Bollgard II this year and it was as severe as it was.”
The producer planted around 1,200 acres in a single Bollgard II variety, for seed production. Original Bollgard fields scattered around the Bollgard II fields “did not have the problem with fall armyworms,” said Heaton, adding that fall armyworms were probably taken out by applications directed at bollworms and plant bugs.
Heaton said he raised Bollgard II cotton varieties in 2002 and did not experience a problem with fall armyworms.
Mullins noted that in a single test in 2003, “post spray boll damage ratings (in Bollgard II) revealed no difference in the sprayed versus unsprayed in boll damage levels. Whether or not it's going to pay to spray Bollgard II on the appearance of larger larvae in blooms is a question we are going to learn through our commercial experience with Bollgard II.
Bollgard II yields this year came in “better than I expected,” according to Heaton, noting that most of it was planted very late. “It set a tremendous top crop, the biggest I've ever seen a cotton plant put on. It looks like the final yield will come in around 950 pounds on that variety (DP 424 BGII/RR). That is comparable with what we're making on other varieties that were also planted that late — around May 25.”