Leaf grade in cotton has risen over the last decade, and recent research by a Texas A&M graduate student indicates that leaf hairiness may be a contributing factor.
Zackary Elder, in a poster presented at the Beltwide Cotton Conferences in Orlando, reported higher leaf grades over the past 10 years resulted in significant dockage to producers.
“Cotton classed through the USDA-AMS classing office in Corpus Christi, Texas, has reported increases in leaf grade values, beginning in 2000,” Elder said.
The issue has created significant economic loss to growers but has also created problems for ginners who have to take extra steps to clean cotton with higher leaf grades.
He emphasized the importance of reducing leaf grades. The best leaf grade score is zero; the worst is 7. Discounts start at 3, at which point producers may lose 3.45 cents a pound. At a leaf grade rating of 4, discount is 3.6 cents a pound. It increases from there by 0.10 cents for each grade increase until it reaches 7 and a 3.80-cent-per-pound discount.
Elder evaluated harvest aid and variety as possible contributors to increased leaf grade during the 2010 and 2011 growing seasons. In defoliation trials, the hairy variety had higher leaf grades than a smooth variety across multiple levels of defoliation in 2010 and 2011.
“Currently, several factors are believed to negatively influence the leaf grade values,” he said. “First is the level of defoliation and desiccation prior to harvest. Second is the influence of varietal characteristics, such as leaf hairiness, bract hairiness and leaf and bract size.”
He said chemical defoliation can be unpredictable, depending on several factors, including harvest-aid selection, plant condition, weather prior to and during application, spray coverage, canopy density, translocation, and varietal traits.
“Additionally, hairier varieties are suspected of contributing to higher leaf grades through a ‘Velcro effect.’”
Elder said hairiness ratings in commercial varieties are assigned subjectively from smooth to very hairy, and ratings can be inconsistent.
His research hypothesis included the assumptions that:
- Higher percentages of defoliation will cause a lower leaf grade in harvested cotton.
- Reduction of desiccation will yield a lower leaf grade in harvested cotton.
- Hairy leaf varieties of cotton will amplify leaf and bract trash, resulting in higher leaf grades than smooth-leaf varieties.
Elder anticipated that increased trichome (fine outgrowths or appendages on plants) density and larger bract size would be contributing factors to leaf grades.
In his variety trails, he collected samples of leaf and bract samples, including grab samples at harvest.
He also developed trials for four varieties and five harvest aids with two smooth and two hairy varieties. Another trial included two varieties ( DP0935B2RF and DP0949B2RF) harvested into individual modules.
Research indicated no correlation of harvest aid or level of desiccation and leaf grade rating. But hairiness did.
“Leaf hairiness influences leaf grade more than defoliation when environmental conditions are conducive for higher leaf grades.” Elder said. “Differences between years indicate specific environmental conditions, such as rainfall after harvest-aid application, are needed for high leaf grade.”
He said trichome density varied between varieties and were similar across all trial locations. “Leaf grade increased with leaf and bract trichome density but leaf and bract size did not correlate with leaf grade.”
Elder said more work needs to be done to give cotton farmers more accurate data from which to select and manage varieties.
“We need to evaluate various physiological traits that may influence cotton leaf grades and other fiber quality characteristics,” he said. “And we need to develop an industry-wide standard for leaf hairiness.”
Elder’s research was supported by the Texas State Support Committee, Cotton Incorporated, Cotton Foundation, and Texas A&M University.