Late planting due to erratic onset of the rainy season is becoming more frequent in the Sahelo-Sudanian climate where cotton is grown, causing seed cotton yield (SCY) loss and higher risk of drought at the end of the crop cycle. Therefore, cultivars should be adapted to late (from July 10) planting date (PD) in Senegal. The aim of this study was to analyse the interaction between genotypes and PD on SCY in Senegal under rainfed conditions. Field experiments were conducted in 2018 and 2019 using a split-plot design (two PDs, eight cultivars) at three experimental stations. Robust analysis of SCY was used to moderate the effect of potential outliers. The average SCY was 1404 kg/ha under early planting, and 714 kg/ha under late planting. The best SCY was obtained under early planting conditions, in environments with good rainfall. The loss due to late planting was significantly affected by cultivar choice. None of the cultivars performed best under both early and late PD. Under early PD, cultivar CS 50 gave the best SCY, while under late PD it was cultivar IRMA Q302. The best performing cultivar on average depended on the proportion of early plantings. A model was developed to identify the best overall cultivar based on the expected proportion of early planting, as a decision support tool for the cotton development company, if only one cultivar is released. The benefit of releasing a second cultivar for late-planted fields is considered.

Chemical defoliants are widely used in cotton (Gossypium L.) to accelerate leaf abscission and boll maturation, as well as, to facilitate mechanical harvesting. The current study was conducted to determine the interactive effect of cotton cultivars and spraying time of defoliant on defoliation, boll opening, fibre yield and quality. An experiment was performed with four cultivars and three defoliant spraying time during 2019 and 2020 in split plot design with three replications. At harvest, the defoliation and boll opening rate of all treatments after spraying defoliant was 94.6 and 85.4%, while the blank control (water) was 73.9 and 79.1%, respectively. After spraying defoliant, the effects of defoliation rate, boll opening rate, fibre yield and quality were different among cultivars, indicating that different cultivars had different responses to defoliant. Among them, L7619 was the most sensitive to defoliant, with the average defoliation rate of 95.6% and a seed cotton yield reduction of 882.9 kg/ha. Among the different time of applications, late spraying (17 September, B3) of defoliant recorded the highest defoliation rate (97.3%), boll opening rate (89.8%), seed cotton yield (3991 kg/ha) and steadily increased the fibre strength by 0.59 cN/tex compared with the control. Late spraying of defoliant had little or even no adverse effect on the remaining fibre quality traits (length, uniformity, micronaire and elongation). In general, these results suggested that the appropriate time for spraying defoliant can be determined based on the sensitivity of the cotton cultivar, the weather conditions at the field and the harvest time.

Short duration cotton (Gossypium hirsutum L.) cultivar may be more profitable for the growers, as it will have shortened critical growth window for drought, heat and insect pests. Therefore, in the present research work, two cotton advance lines IUB-71 and IUB-73 along with an approved cotton cultivar IUB-13 were tested under four different sowing dates i.e. S1 (25th April), S2 (10th May), S3 (25th May) and S4 (10th June) in 2017 and 2018 under field condition. Field layout was RCBD factorial with four sowing dates as one factor and three cotton genotypes as another factor with three replications. Data were recorded for plant height, total number of nodes, bolls per plant, seed cotton yield (SCY), above ground fresh biomass (AGFB) and harvest index (HI). An overall decreasing trend with increasing sowing dates was observed in all the traits except HI that relatively increased in all the three genotypes. Within each sowing date, a higher value for each trait was observed for genotype IUB-73 except for AGFB might be due to higher reproductive allocation. It is concluded that IUB-73 due to superior SCY and HI specifically under late planting is best fit for short cotton seasons with reduced critical window for cotton management.

Field experiments were conducted in 2013 and 2014 to determine the influence of velvetleaf densities of 0, 0.125, 0.25, 0.5, 1, 2, 4, and 8 plants m−1 of row on cotton growth and yield. The relationship between velvetleaf density and seed cotton yield was described by the hyperbolic decay regression model, which estimated that a density of 0.44 to 0.48 velvetleaf m−1 of row would result in a seed cotton yield loss of 50%. Velvetleaf remained taller and thicker than cotton throughout the growing season. Both cotton height and stem diameter reduced with increasing velvetleaf density. Moreover, velvetleaf interference delayed cotton maturity, especially at velvetleaf densities of 1 to 8 plants m−1 of row, and cotton boll number and weight, seed numbers per boll, and lint percentage were also reduced. Fiber quality was not influenced by weed density when analyzed over 2 yr; however, fiber length uniformity and micronaire were adversely affected in 2014. Velvetleaf intraspecific competition resulted in density-dependent effects on weed biomass, ranging from 97 to 204 g plant−1 dry weight. Velvetleaf seed production per plant or per square meter was indicated by a logarithmic response. At a density of 1 plant m−1 of cotton row, velvetleaf produced approximately 20,000 seeds m−2. The adverse impact of velvetleaf on cotton growth and development identified in this study have indicated the need for effective management of this species when the weed density is greater than 0.25 to 0.5 plant m−1 of row and before the weed seed maturity.