Zinc sprays have been successfully applied from airplanes and helicopters, particularly where groves are inaccessible to ground rigs. Air applications require about as much zinc per acre as do ground sprayers in mature groves, but in 10 to 20 gallons of water per acre. Timing normally is not critical, but applications are most effective in June and July, when spring-cycle leaves are expanded. Because zinc does not translocate readily from sprayed leaves to young growth occurring after spraying, severely affected trees may require respraying. The effectiveness of zinc application to the soil depends upon the soil type, the amount used, and the method of application.
Some trees have been injured, so it is wise to try an application on a few trees first.
Chelated forms of zinc may correct the deficiency, but appear to have no advantage over zinc sulfate. In normal maintenance, adjust rates according to leaf analysis values. Per Tree Lbs. Per Tree Gal. Favorable responses have been observed in San Diego County and in Rancho California.