There are a couple of reasons why growers may want to induce early fall defoliation of fruit trees, particularly apple. For some growers crop load management starts with bud counting in October or November, a task that is much easier to do with no leaves on the tree. Growers may have H-2A labor still available after harvest and want to utilize that labor force to begin pruning, again easier to accomplish absent leaves – especially if pruning to bud counts.
Then there is the (mistaken) perception that defoliation automatically equates to early cold tolerance, and the concern around highly vigorous young trees that grow late into the season being particularly susceptible to hard freezes in November or December.
For the past 25 or 30 years, fall defoliation strategies have relied mostly on deliberately induced phytotoxicity from a chemical cocktail mix of high rates of zinc sulfate, often combined with a chelated copper and sometimes urea. The idea is to burn the leaves off the trees. Results from these mixtures have been inconsistent, and even when they do work they cause more harm than good.
The attached paper explains why this isn’t a good idea, and presents an alternative method for fall defoliation.
