Cotton fibers develop to maturity in about 45 days after anthesis (white flower). Most fiber elongation occurs during the first three weeks following bloom, whereas fiber deposition or thickening primarily occurs during the second three weeks of boll development.
Although stink-bug-damaged bolls are often harvestable, relatively few studies have examined the impact of boll feeding on fiber quality.
Preliminary studies using handpicked samples ginned on a tabletop gin showed that fiber length and fiber length variability were negatively impacted by excessive boll damage caused by stink bugs.
Research at Louisiana State University Agricultural Center also found that southern green stink bug feeding significantly affected the physical fiber properties of micronaire, strength, uniformity, and fiber length; however, this study also used a tabletop gin.
Further studies were conducted to evaluate the impact of boll-feeding bug damage on fiber quality of machine-picked cotton processed in a manner consistent with commercial ginning practices.
The studies sought to determine if a mechanical picker will harvest a lower percentage of stink-bug-damaged locks compared to handpicking, and if commercial ginning practices (lint cleaners and other ginning processes) will further impact fiber quality.
Seed cotton from 43 trials conducted during 2005 and 2006 in Georgia, North Carolina, South Carolina, and Alabama was machine picked and ginned using the University of Georgia’s MicroGin, which processes cotton consistent with commercial ginning practices.
Treatments evaluated included aggressively sprayed and non treated plots, and in some locations, one or more intermediate treatments such as protection at various plant growth stages or at a predetermined internal boll damage threshold. Plots ranged in size from six rows wide and 40 feet long to 36 rows wide and 125 feet long and included three to four replications.
At some locations, trials were established in high-risk areas for pest infestations, i.e., near peanut fields, to enhance the likelihood of damaging stink bug infestations. Lint samples were submitted to Cotton Incorporated for HVI fiber-quality analysis.
Results showed that lint turnout and most physical fiber measures were negatively impacted when excessive stink bug damage (significant yield loss) occurred (Tables 1 and 2). Stink bug populations were above thresholds in 2005 trials, and significant yield reductions were observed in untreated plots.
In 2005 trials, all HVI fiber-quality measures, except strength, were significantly reduced in untreated plots compared with both threshold treatments and aggressively sprayed plots.
No significant differences in fiber-quality measures were observed in either 2005 or 2006 when aggressively sprayed treatments were compared with threshold treatments. Figures 5 and 6 summarize all data from the 2005 and 2006 trials that examined differences in fiber quality based on the levels of stink bug damage.
Fiber length decreased as bug damage increased (Figure 5), and yellowness (+b) increased as stink bug damage increased (Figure 6). The current summary indicates that fiber quality is preserved when stink bugs are managed effectively.
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