Influence of Timing of Ethephon Application on Yield and Fruit Composition of Chenin Blanc Grapevines

Abstract

Chenin blanc grapevines at Davis were treated with single applications of 750 ppm ethephon at nine different stages of berry development. The first treatment began at full bloom (>90% anthesis) with eight subsequent treatments sprayed at one week intervals following bloom. Results were compared with an unsprayed control. Overall yield, primary crop yield, and number of primary clusters were significantly reduced in vines treated with ethephon up to two weeks after bloom. Second crop yield and number of secondary clusters were reduced in all ethephon treatments. Ethephon applied at bloom and one week post-bloom significantly reduced °Brix and pH, but increased titratable acidity of fruit at harvest. Ethephon applied six and nine weeks post-bloom increased °Brix without altering titratable acidity or pH, relative to the control. Fruit potassium levels of vines treated with ethephon at bloom and one, two, three and seven weeks after bloom differed significantly from the control fruit when sampled in mid-August, but the effect was transitory with all the differences eliminated by early September.