Ethylene from Diseased Plants

2.5 pounds of lime to 100 gallons of water) or zinc oxide (2 pounds to 100 gallons) may be used. For severe cases in Florida, twice the indicated dosage of zinc sulfate and lime is recommended. Sprays should be applied soon after new growth appears. Iron deficiency occasionally occurs in California, primarily in trees on calcareous soils. It is characterized by yellowing of the major portion of the leaf, with the veins remaining green. Little change is caused in fruit size or shape or in leaf size. Soil applications of sulfur and similar acidifying materials have generally been only moderately successful. Reduction in water applications to trees in the problem soils has usually resulted in a lessening of the chlorosis. Copper deficiency has been reported in Florida on young avocado trees. Symptoms include development of Sshaped shoots and lateral branches, premature defoliation, a multiple-bud condition, and dieback. This trouble is usually corrected by soil or spray applications of copper sulfate. The presence of excess chlorides in soil or irrigation water is the primary cause of tipburn of leaves in California. Tipburn causes a considerable reduction of green-leaf area, with consequent weakening of the tree. The dead areas are also commonly invaded by fungi such as Botryosphaeria ribis, which then spread to the fruit. Control of tipburn is difficult unless water with a lower chloride content is available to use in leaching the soil.