Like all citrus plants, the lemon is an easy prey to pests and diseases, if not maintained properly. The lemon tree is attacked by variety of diseases most of which are not life-threatening, except canker. Understanding water soil and climatic conditions is helpful in keeping these trees free from problems.
Greasy Spot disease is caused by Mycosphaerella citri, a fungus affecting most citrus plants. The most obvious symptom of this disease is chlorosis or yellowing of the leaves that often results in blister-like formations on the upper side of the leaves. The disease is caused by direct transfer of the fungal spores through contact with other infected citrus plants in close proximity. Remedies include spraying the plant with copper or sulfur spray.
A lemon tree infected with citrus scab has fruits that are marked with irregular grayish spots and structures similar to warts. The disease is caused by fungal spores and spreads by wind-driven rain and insects. Controlling it is difficult as it requires strict timed spraying of copper oxychloride, especially after the spring .The disease doesn't affect the interior of the fruit, but causes scarring, reducing the fruit's market value.
European and Mediterranean Plant Protection Organization notes that citrus tristeza caused by the cholsterovirus is the most destructive viral disease of all for citrus plants. It has a global reach and results in stunted growth and dieback for all varieties of lemon trees. The disease is controlled by using tristeza-tolerant rootstocks, but some strains of this virus have managed to still survive in the plant even after using tristeza-tolerant rootstocks.
Most citrus trees are susceptible to root rot .The fungi responsible are Phytophthora citrophthora and Armillaria mellea. Common symptoms are premature leaf shedding and yellowing of leaves. Regular fumigation and applying right amount of pesticides is the only known cure. Water acts as a vehicle for transferring this disease.
Asian Citrus Leaf Miner
Leaf miner is a moth that is native to southern Asia, hence the name. It is a small moth that causes twisting and curling of leaves of the plant. Spraying of oil water sprays is an effective, inexpensive remedy that works within a few days of application. The adult female moths cannot lay eggs on an oily surface.