Effect of hot water treatment and Timorex Gold^® in the control of avocado anthracnose

Avocado anthracnose (Colletotrichum spp.), is an important disease affecting worldwide production. In Chile, the disease is affecting the export industry, while management tools are not available. The aim of this study was to evaluate the effect of hot water alone or mixed with Timorex Gold^® (TG), (tea tree oil a.i.) on avocado anthracnose. Sensitivity to hot water of mycelia of C. gloeosporioides, C. cigarro, and C. pyricola, was evaluated at temperatures of 25, 50 and 60°C. Agar plugs with mycelium of the pathogens were treated for 1 or 3 min, then cooled and plated on potato dextrose agar and incubated at 20°C. ‘Hass’ avocados were harvested from an orchard with high incidence of anthracnose and dipped in water at 25°C (control), water at 50 or 60°C for 3 and 1 min, respectively, water at 50 or 60°C for 3 and 1 min plus TG at 2%, TG at 2%, and prochloraz as a commercial standard. Fruit was stored at 7°C for one week and then left at room temperature. Colletotrichum cigarro was the most sensitive species to hot water with a complete inhibition after exposition at 50°C for 3 min and at 60°C for 1 and 3 min. C. pyricola was completely affected only at 60°C for 3 min. C. gloeosporioides grew after being treated with hot water at both temperatures and exposition times. Immersion of avocados for 1 min at 60°C reduces the incidence and severity of anthracnose similar to the standard fungicide. The addition of TG did not increase the effectivity of hot water. Hot water at 50°C for 3 min and TG alone did not reduce the level of disease. Hot water treatment at 60°C for 1 min did not affect the color of the flesh nor fruit firmness, but it had a negative effect on the skin of the fruits that turned black.