Effect of Ethephon and A Morphactin on Growth and Fruiting of 'Thompson Seedless' and 'Carignane' Grapes

¹ Department of Viticulture and Enology, University of California, Davis 95616.

Ethephon [(2-chloroethyl) phosphonic acid] and a morphactin IT 3456 (methyl-2-chloro-9-hydroxy-fluorene-9-carboxylate) were applied as sprays to 'Thompson Seedless' and 'Carignane' grapes at prebloom, bloom, fruit set, or 2 weeks after fruit set. Ethephon was used at 30, 300, and 3,000 ppm, and morphactin at 0.1, 1, 10, and 100 ppm. On 'Thompson Seedless,' morphactin at 100 ppm resulted in much leaf cupping and abnormal venation. Prebloom and bloom treatments had more formative effects than did later applications. However, axillary bud growth was stimulated by sprays at fruit set and after fruit set. The response of 'Carignane' was similar but less marked. Ethephon at 3,000 ppm applied at prebloom or bloom to 'Thompson Seedless' caused curling of shoot tips and development of abscission layers at the apical nodes.

Ethephon reduced the crop on 'Thompson Seedless' at almost every level tested, and 30 ppm was effective at the prebloom stage. With 'Carignane', fruit set was reduced by all concentrations of ethephon except with the treatment after fruit set. Morphactin reduced the crop of 'Thompson Seedless' the most when applied at prebloom or fruit set, and 'Carignane' was most sensitive at the first three growth stages.

In the season following treatment, bud break was usually delayed on 'Thompson Seedless' that had been treated with ethephon; but morphactin delayed bud break only when 100 ppm was applied at prebloom. Both ethephon and morphactin applied at the high rate usually reduced the number of clusters the following year. Growth of ethephontreated 'Thompson Seedless' vines was weak, especially with the higher concentration. Results with 'Carignane' were similar to those of 'Thompson 'Seedless'. Main veins of the leaves and clusters of 'Carignane' treated with morphactin were fasciated, though vine vigor was normal. With later dates of treatment, damage on leaves and clusters was closer to the apex.