The lemon plant, or tree, is a cold sensitive citrus that is native to India. This small to medium sized tree reaches heights between 10 and 20 feet, and thrives in most well-drained soils. It produces dark green foliage and blooms fragrant flowers with reddish buds and yellow anthers. This tender tree is susceptible to several diseases which can be harmful to the tree and its fruit when left untreated.
Citrus scab is a fungal disease that can be detrimental to the lemon. The University of Florida IFAS Extension explains that this quickly spread disease can infect the foliage, twigs and fruit of the lemon within four days of contact. Spread by fungal spores, the infection begins as small, orange spots that appear on the foliage and fruit. The protruding spots enlarge into well-defined warts that develop a scab-like covering across the surface. The infected foliage will also become distorted and discolored. The scabs on the infected develop in a clustering pattern. The clusters are initially cream colored but darken with age. Severely infected lemon plants will experience growth stunt and fruit drop. Citrus scab can be controlled with scheduled fungicidal treatments and pruning of the infected areas.
Greasy spot is a disease that can have serious effects on the lemon plant. This fungal disease develops on the fallen debris that lies on the ground around the tree. The fungal spores are released as the litter decomposes and transported by wind and rain. The University of Florida IFAS Extension explains that these fungal spores germinate rapidly on the tree when humidity levels rise above 90 percent. The foliage of the infected lemon plant will yellow and the foliage tissue will develop blisters. These blisters will swell and turn into black, necrotic areas. The foliage will also defoliate from the tree, often before the blisters become discolored. Greasy spot can be prevented with scheduled fungicidal treatments and by keeping the lemon's area free of debris.
Blue mold is an aggressive disease that is transported by spores. Unlike most fungal diseases, this fungal disease thrives just as easily in cold temperatures as warm temperatures. The active fungal spores can thrive for long periods in the soil without a host and can quickly contaminate pruning and tree equipment, soak tanks, fruit containers and packinghouses. These fungal spores infect the fruit on the tree through its wounds, oil glands, as well as through its surfaces. However, harvested lemons that are infected with blue mold can also infect other healthy harvested fruit. Initial infections appear as small, watery spots that enlarge into lesions across the surface of the lemon. These water-soaked lesions produce blue colored spores that cover the lesions. The infection penetrates the lemon rind and causes rot of the interior fruit. The blue spores on the lemon rind surfaces also cause cross-contamination and infection of surrounding fruit. Continuous sanitation of equipment and containers reduces the potential of cross infection and contamination. Fungicidal treatments are also effective in preventing and controlling the disease.