ISHS Acta Horticulturae 498: IV International Symposium on Kiwifruit
SUPPLEMENTING WINTER CHILLING IN KIWIFRUIT IN SUBTROPICAL AREAS BY EVAPORATIVE COOLING AND SHADING |
| Authors: | P. Allan, M.J. Savage, T. Criveano, T. Mork, N. Blore |
| Keywords: | Actinidia deliciosa, chilling portions, daily positive chill units, evaporative cooling, shading, subtropics, winter chilling |
| Abstract:
High daytime air temperatures have an adverse effect on accumulation of winter chilling in deciduous plants. An understanding of the role of temperature on the level of the “intermediate product” (reversible reaction) in the dynamic model, illustrates the adverse effect of high temperatures on accumulation of chilling portions (CP). Because the level of the “intermediate” never decreases below zero, daily positive Utah chill units (PCU) can be calculated ignoring negative daily totals. Low-chill ‘Allison’ kiwifruit, growing under different levels of shade (0, 15, 30, 40 and 55%) were evaporatively cooled (EC) by intermittent overhead sprinkling, when daytime air temperatures exceeded 16°C, over the past three years at Pietermaritzburg, followed by 4% Dormex® application in early August each year to promote uniform bud burst. The kiwifruit buds were generally kept from rising to temperatures above 18°C during warm winter days, provided the buds were kept wet. EC has resulted in markedly increased average yields of around 25 kg per plant compared to around 8 kg per plant previously. This increase was also partly due to the unusually cold winters, for Pietermaritzburg, of 1996 and 1997 (more than 400 PCU) compared with winter 1998 (160 PCU). Best yields of around 35 kg fruit per plant were obtained under 30 and 40% shade with heavy shade (55%) being most detrimental. After the unusually warm winter in 1998, even EC vines have had reduced flowering but non EC vines produced very few flowers. EC should be started when night temperatures drop below 12°C and continue until over 500 PCU have been recorded for ‘Allison’ kiwifruit. | |
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