The prevailing opinion is that there’s no one “silver bullet” solution to Georgia’s cotton quality problem. The more likely scenario for improving fiber quality will include multiple factors, such as improved varieties, controlling stink bugs, preventing nematode damage, and proper defoliation and harvest timing.
And while it might be too late to make drastic changes in production schemes this year, there’s still time to fine-tune your defoliation and harvest timing strategies, says Craig Bednarz, University of Georgia plant physiologist.
Bednarz reviewed data from several studies during the recent Cotton Quality Meeting, Field Day and Defoliation Clinic held in southwest Georgia’s Early County.
In looking at harvest data, Bednarz says that for the five-year average, Mississippi and Louisiana cotton is about 90 percent harvested by week 43 or 44 while Georgia is around the 60-percent mark.
Statistics also show that the most active days for planting cotton in Georgia are from April 25 to May 25, with peanuts being planted at about the same time. Producers in Georgia harvest peanuts from Sept. 10 to Oct. 15, and they harvest cotton from Oct. 5 to Nov. 15.
“We’ve been going after our peanuts and letting our cotton sit in the field, and this delay in harvesting is costing us,” he says.
Bednarz also reviewed a study which illustrates how much money growers can lose by allowing cotton to weather in the field.
“In 1999, we maximized yield and adjusted gross income when we applied harvest aids at about 76 to 77 percent open bolls. We lost 13.8 pounds of lint per acre per week for every week we waited past this point. We lost $6.74 in adjusted gross income per acre for every week we waited past 77 percent open bolls,” he says.
In 2000, the study showed that 57 pounds of lint per acre per week were lost past 89 percent open bolls. “We lost $20.32 per acre for every week we waited past 84.7 percent open bolls. We were losing money as the crop sat in the field and weathered. This is due not only to losses in lint yields but also to losses in fiber quality. Just about every fiber quality parameter we measured decreased as the crop sat in the field.”
On a typical cotton plant grown in Georgia, says Bednarz, 69 percent of yield comes from first-position bolls, about 28 percent from second position, and the remainder from third position.
“How open is the crop when it’s 65 percent opened? According to our data, you’re opened all the way up to main stem node 13. Our biggest money positions already are open at 65 percent. At 65-percent open, our biggest money bolls already are beginning to weather.”
The next question, says Bednarz, is how much more of the cotton can be opened with a pound of ethephon. “We don’t have any hard science on this, but we believe — based on observation — that we’re going to open all the way up to main stem 20 if we defoliate the crop at about 65-percent open.”
Georgia cotton growers tend to become concerned, he says, when the crop is ready to pick and they see unopened bolls in the top of the plant.
“Based on our information, there’s about $8 to $10 worth of cotton in the top of the plant that we didn’t pick. Is that worth waiting for? Let’s say we defoliate cotton at 85-percent open, and we’re opened all the way up to 16. With a pound of ethephon, we’re going almost to the top.
“Based on our harvest timing studies, if we wait from 65 to 85-percent open bolls before applying our harvest aids — which would be about one week — we increase yields 1 to 3 percent. That’s about $8 that we’ve added. But we’re not factoring in fiber quality. And at those positions, I suspect quality isn’t that good anyway, and it’s probably not worth that much to you.”
Waiting one week after 85-percent open bolls results in a 9 to 11 percent loss in yield, says Bednarz. “We can speculate that the loss comes from the bottom of the crop. That’s where bolls have been weathering for the longest period of time.
“When the cotton crop is 65-percent open, those bolls at the bottom have been opened for about three weeks. If you continue to wait, they’ll deteriorate further from that point. In a period of two weeks, we went from making another 1 to 3 percent yield at $8 to losing about $40. The question for growers is what is it worth for you to wait before applying harvest aids? If you wait on that top crop — in my opinion — you’re already going backwards. We have more cotton at the bottom than at the top.
“By waiting for that little bit in the top, you’re potentially losing a lot more than you’re gaining. Do you want to wait and pick every last boll? I’d say no. It’s up to you to schedule your harvest program, but at least a portion of your crop probably should be defoliated at 65 percent and then picked in a timely fashion. At 65-percent open, the bottom crop has been opened for about 25 days.”
Both cotton and peanuts are indeterminate crops with long flowering periods, says Bednarz. “The flowers that bloom first will be older, and the flowers that bloom later in the season will be younger. Harvest timing is a compromise.”