DORMANCY BREAKING CHEMICALS; EFFICIENCY WITH REDUCED PHYTOTOXICITY

The use of chemical sprays to help in overcoming dormancy is a wide-spread practice in warm-climate countries that grow temperate fruit crops which require exposure to chilling to overcome the dormant period of the buds. An interest in this practice also comes from green-house grown temperate fruit crops for purposes of advanced ripening or environmental protection. With global warming, increased interest in this practice is also developing from more temperate zone countries. Two main problems confront the use of such chemicals: human and environmental toxicity and phytotoxicity especially in stone-fruit species. As a result of the former, many potent chemicals were taken off the market leaving very few options for the grower. As to phytotoxicity, many of the efficient chemicals in use like Dormex, and mineral oils pose a risk to the tree under specific environmental conditions. Other chemicals, having an effect, are not potent enough to compensate for the lack of chilling. Therefore, we initiated experiments with new dormancy breaking agents to achieve strong effects, low phytotoxicity and minimal human hazard. Thidiazuron (TDZ) was reported to have a dormancy breaking effect. We have tried it in Israel, alone and in combination with mineral oil. Results have indicated that this agent is a potent dormancy breaking chemicals in stone fruit species. It is more powerful than any other chemical that we have tested. Its phytotoxicity depends on the species and on the timing of spray relative to chilling accumulation. It may induce trace buds to break, thus it may be important in renovation of older trees. In a different set of experiments we examined the effect of added spreaders/penetrants like Armobreak to a few nitrogenous salts. Trials in peaches and sweet cherries indicated strong effects to various salts when the adjuvant was added to the spray.