Avocado is a native fruit of tropical America and thrives in subtropical and tropical weather. The evergreen tree grows up to 30 feet tall with 3- to 16-inch-long, leathery, elliptical foliage. A fungal disease leads to brown spots on tree foliage.
Avocado is susceptible to anthracnose, a fungal disease caused by Colletotrichum gloeosporiodes. The fungal spores are most active during humid and wet weather. Cooler temperatures less than 59 degrees Fahrenheit stop the spread of disease.
Initial symptoms of anthracnose include the appearance of yellow spots on foliage. As disease progresses, the spots turn brown and enlarge in size, covering the entire foliage surface. There is necrosis or dark borders on margins, veins and tips of foliage. New shoots display purple or brown spots and infected flower heads die. Lesions also spread to fruit.
Prune and remove all infected tree areas. Keep the growing area clear of fallen foliage to keep fungal spores from spreading. Thin the canopy to let light and air into the inner tree. Chemical control options include the use of copper hydroxide sold under various trade names.