The Meyer lemon tree is actually a cross between a true lemon tree and a mandarin orange or sweet orange tree. It was introduced to the United States in 1908 and became extremely popular because it blooms throughout the year in some climates and has a delicious fruit and beautiful blooms. However, Meyer lemons are susceptible to a few diseases, and you need to be aware of the signs and symptoms of them in order to keep your fruit trees happy and healthy.
Asian Citrus Miner
The Asian citrus leaf miner is an infection that is unique to lemon trees, and Meyer lemons are definitely at risk. The leaf miner attacks when the leaves first start growing and are about an inch long. Leaves end up stunted and distorted. Removing the problem manually using sterile pruning should eradicate the issue as long as you completely dispose of debris rather than letting it fall to the ground. You can apply citrus oil just before you expect a "flush" of new growth to try to deter leaf miners in March, May, July and September.
Meyer Lemon Scab
Lemon scab is caused by a fungal infection called Elsinoe fawcetti. The scab first creates small, raised, rough areas on the surfaces of the tree's leaves. These scabs may be yellow, orange or brown, and ultimately the fruit may develop pink, gray or brown rough spots. Additionally, fruit on Meyer lemon trees with scabs tends to be very large because much of the fruit falls prematurely and the remaining fruit receives extra nutrients from the tree. To prevent this disease, treat the tree with copper oxychloride and white oil when about half the petals have fallen from the flowers.
Red Algae Infection
Red algae can grow on Meyer lemon trees in late spring when the weather is cool and humid. You can see the growth on the trees, usually on branches and leaves. You can help prevent this growth by watering your trees only when the soil is dry, and early in the morning. Do not water throughout the day or saturate the soil to the point that it is muddy and creates a muggy environment around the tree. You can spray Meyer lemons with a copper fungicide to help prevent and eradicate red algae infections.