Dynamics and Distribution of Trunk-injected Phosphite in Coconut Palm

Abstract

Palms are an important component of landscapes in tropical, subtropical, and Mediterranean climates, but are anatomically very different from broadleaf trees. Very little is known about the movement and persistence of systemic fungicides into various parts of the palm canopy. This information is critical in selecting fungicides that may be effective against diseases that infect specific parts of the palm. In this study, potassium phosphite was injected into mature coconut palms (Cocos nucifera) at rates of 0, 30, 60, or 90 mL per tree. Various leaf tissue samples were collected periodically thereafter up through 60 weeks and were analyzed for phosphite concentrations. Phosphite moved quickly into leaflet tissue, but concentrations dropped off sharply between 1 and 5 weeks after injection. This drop in leaflet concentrations was balanced by a concomitant increase in spear leaf concentrations. Phosphite persisted at high concentrations in basal rachis tissue of both old and new leaves throughout the experiment. This suggests that this material may be useful for controlling diseases that infect spear leaves and petiole or rachis tissue, but not leaflets.