It’s expected that cotton acreage in north Alabama’s Tennessee Valley could drop from just over 99,000 acres in 2008 to below 75,000 acres this year, says Tim Reed, entomologist with the Alabama Cooperative Extension System.
This past year, he says, some farmers in the region thought they might be able to make money by growing conventional cotton, and a survey of consultants identified seven farmers in the area who planted a total of 1,700 acres of conventional cotton scattered over four counties last year.
“It’s hard to produce any type of cotton presently and make a profit, and in 2008, farmers who planted conventional cotton hoped for a light insect year that would allow them to hold down insecticide costs and, with enough rain, perhaps clear a profit,” says Reed.
Unfortunately, he adds, most conventional and biotech cotton fields had to be sprayed at least once for plant bugs by the end of June and this released a mixed population of tobacco budworms and bollworms that were expensive to control and that reduced yields.
“The only way a scout can estimate the percentage of tobacco budworm and bollworm larvae in a cotton field as eggs begin to hatch is by observing moths as they fly ahead of them while walking through the cotton. Tobacco budworm moths were common last year in late June and the first week of July,” he says.
An examination of 13 larvae collected from unsprayed conventional cotton at the Tennessee Valley Research and Extension Center at Belle Mina showed that at this location, the first infestation of worms was about 50-percent tobacco budworms.
The earliest worm sprays in north Alabama last year were made the last week of June when worm numbers were as high as 20 per 100 plants, says Reed. “Low-cost pyrethroids were unable to take out the tobacco budworms and more expensive chemistry was then used. Plant bugs continued to be a problem after bolls began to develop and one or more plant bug sprays were required starting in mid-July. These July plant bug sprays continued to suppress beneficials and allow worms to build in conventional cotton again by the last week in July.
“Additional worm sprays were required in conventional cotton to prevent more losses. Worm pressure in north Alabama was greater in 2008 than what is considered as ‘normal,’ and a study conducted by Extension Agronomist Charlie Burmester and I showed just how damaging these Heliothine larvae were,” he says.
This study, he explains, investigated the economic consequences of using different cotton variety technology systems in north Alabama. The study compared three varieties — two biotech varieties ST 4554 B2RF and Phytogen 485WF, and a conventional variety, CT 210. Half the plots received pre-plant herbicides and half did not. Some plots received bollworm/budworm sprays and some did not. Plant bugs were controlled in all plots.
The PHY variety, reports Reed, had a significant yield increase from a single pyrethroid over-spray on Aug. 25. Also, the conventional cotton plots at the TVREC that were treated for plant bugs, but not worms, picked 498 pounds of lint per acre less than conventional plots that were treated for both plant bugs and worms.
Worm control costs in conventional plots for two applications of Belt and one pyrethroid spray totaled about $35 per acre, says Reed, which made the Bt tech fees of less than $20 per acre for biotech varieties look like a good deal.
“If we determine value of production per acre for each variety by multiplying lint yields by loan value and deduct the cost of seed plus tech fees and the cost of herbicides and insecticides and look at the net returns for the most profitable treatment combination for each variety, we see that with irrigation, the CT 210 conventional variety netted about $120 less per acre than the biotech varieties.”
Reed says he scouted three 30-plus acre fields of conventional cotton in Franklin County last year during the entire growing season and two of the fields never saw square retention drop below the 80-percent threshold. One field saw the square retention drop to 70 percent, but the farmer elected not to spray due to concerns over developing worm problems, says.
“Gin records showed the three conventional fields which never received any foliar insecticides averaged 1.2 bales per acre. Inspection of fields after bolls began to open in the top portion of the plant showed that plant bug and probably some stink bug feeding caused some locks to develop abnormally and reduced yield.
“In my opinion, the threat of tobacco budworms following June sprays for plant bugs and the increased risk of developing severe weed problems in comparison to herbicide-resistant cotton varieties will contribute to a reduction in conventional cotton acres in north Alabama in 2009. This reduction in conventional acres will probably be greater percentage wise than the percent reduction in total cotton acres.”
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