December 1, 2007
Studies were conducted in the winter, spring, and fall of 2006 on mature trees to evaluate the potential of diquat (Reglone) spray as a defoliant in case of a canker outbreak. All sprayed leaves were killed after Reglone application. Leaf defoliation gradually increased from 0% at 1 day after treatment application to 90% of grapefruit leaves in the winter. Using 1 or 2 pt/acre of Reglone, grapefruit leaves were defoliated 79 to 84% and orange leaves were defoliated 83% to 85% 14 days after treatment application in the spring. In the fall season, defoliation was 83% and 74% of grapefruit leaves, and 90% and 73% of orange leaves using the 1 and 2 pt/acre rates, respectively. Further shaking of tree limbs achieved 100% defoliation. Similarly, fruit drop was increased with time until 14 days after treatment application in the spring and fall seasons. Fruit drop 14 days after treatment application was 94% for grapefruit in the spring and 95% of grapefruit and 100% of oranges in the fall with the 2 pt/acre rate. Shoot desiccation was also increased at 14 days after treatment application. Regrowth of new leaves from the end of desiccated shoots increased with time as >95% of the grapefruit branches had regrown with new flush and 15% to 20% of orange branches flushed 28 days after application of both Reglone rates. Thus, application of Reglone at 1 pt/acre may be enough to defoliate leaves or fruit within 14 days after treatment. It remains to be determined if such defoliation can reduce the potential spread of citrus canker disease.