Foliar Application of Defoliants before Winter Chill Accumulation Advances Budbreak and Improves Fruit Earliness of Blackberry under Subtropical Climatic Conditions

In subtropical blackberry ( Rubus L. subgenus Watson) production, inadequate winter chill causes poor and erratic budbreak, whereas high temperatures heavy rainfall deteriorate late-season fruit quality. We examined the effects of four defoliants [zinc sulfate (ZS), potassium thiosulfate (KTS), urea, lime sulfur (LS)] on defoliation, yield, quality ‘Natchez’ grown under chilling conditions in two consecutive growing seasons. Plants were treated with at 187 kg·ha −1 via spray application (1870 L·ha ) beginning accumulation (late December). A nonionic surfactant (Agri-Dex) was added 0.5% (v/v) to all treatments including water control. Cumulative hours (<7.2 °C) experiment site 209 134 first second seasons, respectively. Defoliation only 40.2% 55.5% control, but it induced moderately by LS (69.7% 84.7%) severely other (81.7% 94.7%). Budbreak most rapidly urea application, followed LS, KTS, ZS, advancing 17 66 days compared Consequently, ZS increased early season yield 2.79, 2.55, 0.87, 0.31 t·ha , respectively, control (0.12 ). By contrast, final percentage budbreak total-season did not show significant treatment effects. KTS caused cane dieback bud mortality, resulting lowest among treatments. Importantly, had no negative impact berry size soluble solids concentration. These results suggest that are effective dormancy-breaking agents for they could be an important adaptation tool production. Among three defoliants, appears ideal chemical option because its consistent efficacy, favorable safety profile, low cost.