THE USE OF GROWTH REGULATORS TO AID THE MECHANICAL HARVESTING OF RASPBERRIES - AN INTERIM REPORT

The force needed to detach Malling Jewel raspberries was determined at 2 to 3 day intervals following an application of Ethrel (300ppm a.i.) or ascorbic acid (1.0%). Variability was high and significant differences occurred between picks but not between treatments.

Malling Jewel and Glen Clova were harvested with a 'vibrating drum' harvester and the effects of prior treatment with Ethrel (150ppm and 600ppm a.i.) or ascorbic acid (0.5% and 3.0%) determined. Malling Jewel was harvested 4, 7 and 11 days after spraying, and Glen Clova on the first two of these dates. The proportion of ripe fruit of Malling Jewel removed was uniform over the harvests, but varied with Glen Clova. Both rates of Ethrel increased the amount of ripe fruit removed at the second harvest of both varieties, while 0.5% ascorbic acid was effective at the second and third harvests of Malling Jewel.

Ethrel (500, 1000 and 2000ppm a.i.) was applied to Malling Jewel and Glen Clova at the onset of ripening and as yields began to decline at the end of the season. Ripening of both varieties was enhanced by the early application but the effect varied between varieties, with concentration and with time of application. The late application affected the ripening of Malling Jewel fruit but, as with the earlier sprays, the duration of the effect was brief. Leaf senescence was enhanced and yields substantially lowered by Ethrel, to a greater extent in Glen Clova.

Exogenous ethylene production by detached Malling Jewel and Glen Clova fruits, and the effect of a single Ethrel (2000ppm a.i.) application, were determined. Ethylene levels were naturally high and the response to Ethrel varied with variety, time after spraying and the stage of development of the fruits at the time of application.