The Meyer lemon is a cross variation of the lemon and the mandarin orange. Meyer lemon trees produce smooth, thin-skinned, round lemons. The lemons are sweeter and less acidic than the standard lemon. Meyer lemon trees thrive in full sun and produce blooms and fruit throughout the year, but especially from December through April. This constantly growing tree is susceptible to several diseases. When left untreated, some of the diseases can be injurious to the tree.
Citrus scab is a fungal disease that can result in severe injury and disfigurement to the Meyer lemon. The disease is transported by spores that lie dormant in old fruit and debris during the winter months. The spring rains and winds transport the fungal spores onto the newly developing foliage and fruit, which causes infection. Newly developing foliage is susceptible to citrus scab for only its first few days. Developing fruit can be susceptible to citrus scab for up to two months.
Infected foliage will develop small, circular spots that are slightly elevated with a pale orange color. The developing spots will form into wart-like growths that will become covered in scabby tissue. The infected foliage will also appear distorted and crinkled.
On infected fruit, look for scabby, olive-colored masses and lesions. Symptoms generally begin to appear four to seven days after infection. Control citrus scab with regular applications of fungicidal sprays, which are typically applied in the early spring and late fall.
Citrus anthracnose develops during long periods of wet soil conditions. This fungal disease is transported by fungal spores that infect the rinds of the Meyer lemon. Infected lemon trees will also experience growth stunt, premature defoliation and fruit decay. As the infection continues, infected foliage and twigs will become overwhelmed with dark-colored fungal spores. The diseased fruit may also develop fungal fruit bodies.
Fungicidal treatments, along with pruning of infected areas, are effective in controlling the disease. Apply fungicidal treatments in the fall at the end of the growing season. The tree should be evenly covered with the spray to ensure its effectiveness.
Greasy spot is a fungal disease that infects the foliage and fruit of the Meyer lemon. Like many fungal diseases, this fungal disease develops during rainy, wet periods. The fungal spores lie dormant in the decomposing debris that lies around the tree. These spores are released by the rains and winds and infect the foliage of the Meyer. Infected trees will show initial symptoms on foliage. The symptoms include the formation of brown and yellow foliage spots, blisters and swollen foliage tissue.
Progression of the disease causes the foliage to turn black, collapse and die. Premature defoliation of infected foliage will also occur. One to two fungicidal sprays are effective in controlling citrus greasy spot. The first application should be in midsummer, with the second application around mid-fall.