Uptake, movement, and persistence of fungicides in mature coconut palms in Florida, U.S.

Abstract

Palms are arborescent monocotyledons, with a vascular system different from eudicotyledonous trees. Compared to broad-leaf trees, very little is known about the uptake, movement and persistence of systemic fungicides into the palm canopy. In this study, conducted in 2010 and 2012, four systemic fungicides were examined in coconut palms (Cocos nucifera) in Florida, U.S., using three different application methods. A bioassay method was used to detect the fungicides every four to five weeks in palm rachises located throughout the canopy. Thiophanate methyl, which can only be applied as a soil drench, was never detected. The same was true when propiconazole and thiabendazole were applied as soil drenches. Tebuconazole, applied via infusion, was also never detected, but this appeared to be due to formulation issues. Propiconazole was detected in only two of four palms in 2010, when applied via infusion. The labeled rate had increased by 2012, and when this new rate was applied via pressure injection, the fungicide was detected in all four replicate palms. Thiabendazole, when applied via infusion or pressure injection, was detected in all four replicate palms in both years. Propiconazole and thiabendazole persisted uniformly in the canopy for at least eight weeks after application, but amounts tapered off after that time. Neither fungicide was detected in any portion of the canopy after 28 weeks. Both fungicides were detected in leaves that emerged after their application. This suggests that these fungicides may be useful for controlling some canopy diseases.