O. Gormus - Department of Field Crops, Faculty of Agriculture, of Cukurova, Adana, Turkey.
A. El Sabagh - Department of Agronomy, Faculty of Agriculture, Kafrelsheikh University, Egypty.
F. Kurt - Department of Field Crops, Faculty of Agriculture, of Cukurova, Adana, Turkey.

Defoliation is an important management practice of cotton production. Field experiments were conducted for exploring response of cotton to defoliant application times at various percentages of boll opening on seed cotton yield and fiber quality. Experiments were arranged in split-plot design with defoliation times (control, ۴۰, ۶۰, and ۸۰% open boll) as the main plots and cultivars (hairy leaf, semi-smooth leaf, and smooth leaf) as subplots, with three replicates. The pooled results indicated that early application of harvest aid products significantly reduced seed cotton yield, boll number per plant, micronaire and fiber length. Significant reductions in seed cotton yield occurred with defoliant applications both prior to and after ۶۰% open boll application timing. Application at ۴۰% followed by boll opening had the maximum number of the green leaves remaining on the plant at ۱۴, ۲۱, and ۲۸ days after treatments and a corresponding high trash content and high leaf grade. However, except for the leaf grade, the number of green leaves remaining on the plant after defoliation and the trash content, varietal differences were non-significant. Smooth leaf cultivar (SG ۱۲۵) had the highest number of green leaves left on the plant after treatment (۷۹.۲) compared with hairy (۷۱.۹) and semi-smooth leaf (۷۷.۱) cultivars. It was concluded that cotton cultivars with varying levels of leaf hairiness impacted the defoliation efficacy of the harvest aid products.

Harvest aids, Leaf hairiness, Micronaire, Open boll percentage, Trash content