Seven years of hiding must have been enough for Mid-South tobacco budworms. In 2002, the pest returned to the region's cotton fields with a vengeance comparable to the infamous 1995 invasion, in which the voracious pest often stripped entire fields of bolls.
Fortunately, cotton growers were able to put up some formidable resistance this time around, according to Crawfordsville, Ark., crop consultant Chuck Farr.
Farr of Mid-South Ag Consultants, Inc., says 2002 was the worst insect year he's ever experienced, much worse than 1993 and 1995. “If we had conventional cotton only, the damage would have been as bad or worse than it was in the hill country of Mississippi in 1995.
Tobacco budworms weren't the only problem pests. Other critters included plant bugs, cotton bollworms and fall armyworms. The insects started early and finished late, noted Farr.
“From cotton emergence on in the spring, it was cold, wet and cloudy,” the consultant said. “There was lots of stunting of cotton. Growers sprayed for thrips two or three times. From there, cotton started squaring, and plant bugs and budworms moved in. In June, the main problem was plant bugs. In July and August, lepidopteron species (bollworm, budworm, armyworms) were a constant problem. The insect pressure was worst up and down the Mississippi River.”
A worrisome pattern emerged in budworm populations as the season progressed. “There were 200 percent egg lays, a four- or five-day break, then another round of 200 percent egg lays,” the consultant said. “We had continuous egg lays for six solid weeks, with insects constantly emerging. Sixty to 70 percent of these emerging insects were budworms, the balance bollworms.”
It wasn't unusual for a grower to spend $120 per acre in worm insecticides and applications in conventional cotton, according to Farr. That made the Bollgard technology fee of $24 to $26 an acre a cost-effective input for many growers.
“You can plant Bollgard five years in a row and never have a bug, then have a year like 2002, and you'll still be money ahead,” Farr says. “The money that growers spent on insecticides this year would carry them far down the road in terms of Bollgard tech fees.”
Farr said that in 2002, conventional cotton required an average of five to seven sprays at a cost of $15 per application. Most common materials used were pyrethroids, Tracer and Curacron. Later in the season, Intrepid and Steward were sprayed for fall armyworms.
About 80 percent of the cotton acres scouted by Farr is Bollgard cotton, most stacked with the Roundup Ready trait. One factor driving Bollgard is the lack of suitable Roundup Ready-only varieties, pushing many growers toward stacked cotton.
The latter worked in growers' favor in 2002. On average, Bollgard cotton was sprayed less than one time, according to Farr. Most insecticide applications were for fall armyworm, the pest that caused the bulk of damage to Bollgard cotton this year. “If I pulled 100 damaged bolls from Bollgard cotton, 80 percent of the damage would have been caused by fall armyworms. Fall armyworms caused etching on the bracts and usually tunneled into bolls at the base of the boll, which is the softest part.”
The worms tended to be in the lower two-thirds portion of the plant, according to the consultant. “The threshold numbers were more in the middle to lower part of the plant. The worms that low on the plant were harder to hit with an airplane.”
In the past, the pest has shown up in isolated pockets, but it was much more widespread in 2002. Farr thinks that the high acreage of corn and sorghum is what attracted so many fall armyworms.
Farr noted that in eight out of 10 economic comparisons he prepared, Bollgard won over Roundup Ready only and conventional cotton varieties.
Most of the benefit is in lower control costs, according to Farr. “I have some Bollgard fields that I didn't spend $20 an acre on and some conventional fields that I may have spent $90 an acre on.
“I know the Bollgard tech fee is a lot of money up front. But a lot of times, Bollgard will pay for itself in air or ground applications that you have to make on a non-Bollgard cotton.”
Another contributing economic factor in favor of Bollgard cotton is the often misunderstood concept of sub-threshold control.
But Farr and his growers are starting to get the picture. “The university threshold is one larvae per 3 row feet. If you have one larvae per 4 row feet or 5 row feet or 20 row feet, you're taking damage. It took a little while, but several years ago, we realized there was quite a bit of benefit to that sub-threshold level of control that we were getting. We were probably getting our money back out of the Bollgard just by having that sub-threshold control out there.”
New Bollgard II technology, which will be available in limited supplies in 2003, “would have helped greatly this year for armyworms, loopers, bollworms and leaf perforators,” Farr said. “We would have been able to greatly trim some insecticide bills with Bollgard II.
Each year in the Delta is different with a new set of lessons learned. Here's what Farr picked up from 2002:
“In conventional cotton, be very conscientious about tobacco budworm. This pest is relatively new to the northern Delta. You'd better scout hard, early and pull the trigger on insecticide application when it's time. You'd better kill that first generation, or you'll never catch up with the budworm.
“With Bollgard, it's essential that scouts do a whole-plant search, just like you would in conventional cotton.
“With armyworms in Bollgard cotton, better treat that first generation at first opportunity, almost the moment that threshold is reached.”