Rainfall within several hours after GA treatment on Delaware grapes to make them seedless markedly reduces the formation of seedless berries, which is presumably due to leaching of GA. Therefore, some effective additives to GA solution would be desirable to growers to prevent lowering of GA action on grapes due to rainfall.
This experiment was undertaken to examine the effectiveness of some coating agents added to GA solution on the formation of seedless berries. Coating agents used were mainly composed of acrylic resin or calcium carbide. The treated vines were exposed to the artificial rainfall of 8 mm per hour by sprinkler 2 and 4 hours after GA treatment, respectively. The results obtained were as follows :
In the plots of rainfall 2 hours after GA treatment, each coating agent was not effective to prevent lowering of GA action on the formation of seedless berries. On the other hand, in the plots of rainfall 4 hours after GA treatment, coating agents composed of acrylic resin were effective to some extent, though those composed of calcium carbide gave inconsistent results. They did not at all affect cluster elongation and berry enlargement, quality and appearance.