Abstract
In order to develop effective control methods against freezing injury in Japanese chestnut trees, the effects of treatments intended to restrict water uptake by roots during winter were examined. Three kinds of treatments were tested: root pruning, root loosening and soil application of molasses. Although intensive root pruning (38% of the whole root was eliminated) in January effectively suppressed the occurrence of freezing injury, the treatment may cause undesirable effects on tree growth. The other two kinds of water stressed treatments, root loosening (making a number of cracks throughout the root zone soil with an excavator) and molasses application into root zone soil, successfully avoided this problem.
Both treatments delayed the spring-time increase in twig water content and effectively protected chestnut trees from freezing injury without causing any harmful effects on their growth.
For molasses application (Brix 77.2, total sugar content 50.2%, specific gravity 1.4), half strength solution (diluted with same weight of water) was more effective than quarter strength solution. For 2 or 3-year-old trees, 5kg molasses/tree (sprinkle half strength solution and let the solution permeate into root zone soil) was enough to avoid freezing injury. For 4-year-old trees, 10kg/tree was enough, but the solution should be injected with pressure (20kgf/cm2) into the root zone soil.
