The Effect of Controlled Defoliation in the Sultana Vine

Abstract

About four weeks after anthesis, one of six defoliation treatments was given: control; removal of all nonfruiting shoots; removal of two-thirds of the remaining leaves; and removal of one-third of the remaining leaves taken from single whole shoots, from all shoots from whole canes, or from the basal nodes of all shoots.

Berry development (expressed as soluble solids per berry) was reduced in the season of treatment by 10% (for the least severe defoliation) to 35% (for the most severe defoliation). It also reduced bud fertility (number of bunches per node) in the following season, the effect becoming greater with increasing levels of defoliation. This reduced yield by as much as 80% not only from fewer bunches per node but also fewer berries per bunch.

In the season of defoliation, fruit development on both foliated and defoliated shoots was reduced in the presence of defoliated shoots, especially where both types of shoots were on the same cane. The effect of defoliation on bud fertility was localized within individual shoots.

The incidence of heat injury was not increased by the greater exposure to full sunlight of berries on defoliated plants.