The key lime is also known as the Mexican lime. This low-growing citrus has a vigorous growth rate and can reach mature heights up to 13 feet. This Indo-Malayan native produces rich green foliage and blooms fragrant, purplish-white blooms. This small fruit tree is adaptable and is easily cultivated in pots, as well as the backyard environment. This cold-sensitive tree is susceptible to several diseases which can be injurious, if not fatal, to the key lime tree.
Collar rot, or phythophthora root rot, is a soil-borne fungal disease that enters the key lime through its root system. This water dependent disease develops during long periods of wet, cool temperatures. This disease commonly appears on trees that rest in waterlogged and poorly drained soils. Infected roots become restricted and decay. This decay prevents the system from successfully passing water and nutrients throughout the tree. Infected trees develop symptoms that include wilting and yellowing of foliage, growth stunt, chlorosis, foliage and twig blight, dieback and premature defoliation. There is no cure for collar rot of key lime and infected trees should be removed. The planting area should be fumigated with a fungicidal treatment after the tree is extracted.
Fusarium oxysporum is a fungal disease that causes wilt of the key lime tree. This soil-borne disease germinates and travels via fungal spores during the wet, warm periods of late spring and early summer. These fungal spores enter the tree through the root system and infect the vascular system of the key lime tree. The infected xylem tissue becomes unable to pass nutrients and water throughout the tree. This restriction results in yellowing and drooping of foliage, wilting, dieback, growth stunt, fruit drop and premature defoliation of the key lime. Severely infected trees are overwhelmed by the lack of nutrients and interior defoliation and dies from damage caused by fusarium oxysprum, or fusarium wilt. There is no cure or fungicidal treatment available for this disease.
Anthracnose is a leaf spotting disease that can cause damage to the fruit of the key lime tree. This fungal disease is transported by fungal spores during warm, rainy periods. These spores land on the developing fruit of the key lime and infect the upper layers of the rind. Along with spotted and discolored foliage, infected key lime trees experience bruised and spotted rinds. The small rind spots develop into larger, dark-colored lesions with pinkish-colored fungal masses. Anthracnose can be controlled when it is treated early. Infected fruit and foliage should be pruned away. Fungicidal treatments that are designed to treat anthracnose are effective in controlling symptoms and reducing susceptibility.