Bronze wilt was an issue for the cotton industry in the 1990s but mentions of bronze wilt in the literature were minimal until cotton leafroll dwarf virus (CLRDV) was observed across the cotton belt beginning in 2017. In 2024, bronze wilt symptoms were observed at high levels in Southwest Georgia. University of Georgia on-farm cotton variety trials (10 varieties evaluated across 19 locations) were used to quantify susceptibility to expression of bronze wilt symptoms and impacts on lint yield. Overall, the four varieties evaluated were determined to express bronze wilt symptoms; an additional variety outside the trial program was determined to be susceptible based on observations in grower fields. Differences in symptom severity were observed among locations, with some showing significant yield impacts, whereas others were unaffected. Averaged across non-yield-limiting locations (14 out of 19), 2 to 3% symptomatic plants were observed in symptomatic varieties: symptoms increased to 28 to 35% averaged across yield-limiting locations (5 out of 19). Where yield was affected, bronze wilt symptoms reduced lint yield 16 to 32% in the four susceptible varieties. Across all locations, a negative linear relationship was observed within susceptible varieties: a 1% increase in symptoms resulted in a 0.54% decrease in relative lint yield. These data are the first from replicated research to document yield losses associated with bronze wilt symptoms. Future research should evaluate in-field variety screening methods, genetics of susceptibility to expression of bronze wilt symptoms, and controlled environment experiments to replicate symptoms.
Assessments from the U.S. Environmental Protection Agency suggest that some insecticides can be affected by usage restrictions or label vacatur in the future. An experiment was conducted in Stoneville, Sidon, and Glendora, MS during 2023 to determine the effects of excluding insecticide classes for the control of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), on DP 2131 B3TXF ThryvOn cotton and DP 1646 B2XF cotton. Treatments were replicated in both the ThryvOn and non-ThryvOn varieties and included a season-long untreated control, all classes available for use, all classes except neonicotinoids, all classes except pyrethroids, all classes except organophosphates, and all classes except sulfoximines. Plots were scouted weekly to monitor tarnished plant bug densities and applications were made to plots independently using the best available insecticide options when each treatment reached established plant bug thresholds. Results indicated no significant differences in yield among exclusion class treatments in either variety. Significant reductions in yield were observed in the untreated control plots compared to plots that received insecticide intervention in both the ThryvOn and non-ThryvOn technologies. However, there were no significant differences between the economic returns of the untreated control plots compared to the plots receiving insecticide intervention in the ThryvOn technology. This evidence suggests that if insecticide usage is restricted from a single class, comparable yields can be achieved. However, it should be noted that any loss or reduction in insecticide usage currently used for tarnished plant bug control would result in increased selection pressure on the remaining insecticides, ultimately increasing resistance to those classes that remain available.
Experiments were conducted at the Delta Research and Extension Center in Stoneville, MS during 2022 and 2023 to investigate the impact of irrigation and simulated late-season damage of tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), in cotton. The whole-plot factor compared a 90-centibar irrigation threshold and a non-irrigated treatment. Subplot factor A involved simulated damage by manual removal of squares during the fourth and fifth week of bloom. Three levels of damage at 0, 50, and 100% removal of squares above the uppermost first position white flower was subplot factor B. To understand agronomic impacts and compensation, plant heights, total node counts, nodes above white flower (NAWF), and nodes above cracked boll measurements were recorded beginning at the first week of bloom. Yield was also recorded from each plot. Results from 2022 and 2023 showed significant increases in NAWF from 100% fruit removal during both removal weeks compared to all other removal treatments; however, all treatments remained below five NAWF. No significant yield differences were found among any factor except irrigation. Threshold irrigated cotton had significantly greater yields than non-irrigated cotton. Results from this experiment agree with previous research suggesting insecticide termination could occur after the fourth week of bloom with minimal impacts to plant maturity and yield in both irrigated and non-irrigated situations.
Cotton leafroll dwarf virus (CLRDV) is an aphid-transmitted virus recently identified across the Cotton Belt region of the U.S. Yield responses to CLRDV have been inconsistent, and asymptomatic infections can occur in which no losses are apparent. Conditions underlying the observed variation in yield responses are not understood. A three-year field study was conducted to examine whether yield loss caused by CLRDV is influenced by the age of cotton plants at the time of infection. Timing of infection was investigated by infesting caged plots of cotton with viruliferous Aphis gossypii to transmit CLRDV at different seedling growth stages, beginning after seedling emergence and continuing weekly for three to four weeks. Timing of infection impacted yield only in one out of three years suggesting that plant age is not a primary factor contributing to CLRDV-related yield loss. Future studies are needed to identify the environmental factors influencing disease severity and yield loss.
Increased lint yield of cotton (Gossypium hirsutum L.) cultivars is the primary objective of most cotton breeding programs. Partitioning lint yield into yield components can provide the opportunity to improve lint yield by indirect selection. Lint yield can be defined as the product of lint index (LI) and number of seed per area (SPA). A subjective yield-component rating (YC1) of relative ranks of LI and SPA in University of Arkansas (UA) strain tests has been used to identify lines that have favorable relationships of LI and SPA. An objective, computer-generated application, yield component score (YC-score), available to identify these lines. We were able to generate four years of YC-scores for the 67 UA lines released since 2007. High correlations between YC-score and YC1 indicated that YC-score captured the intent of the YC1 ratings. YC-scores of the 67 released lines were relatively consistent over years of testing and varied greatly among the lines. YC-score was calculated for entries in eight Regional Breeders' Testing Network (RBTN) tests and correlated with lint yield and other yield component variables. YC-score varied among entries in each RBTN test. Correlations with YC-score were highest for LI, SPA, fibers per seed, S-score, and seed index. Negative correlations between YC-score and lint yield in all eight RBTN tests indicate that it should not be used as a primary selection tool. Among high performing cultivars, YC-score can differentiate those that have the most favorable yield component values.
