How to Cure a Lemon Tree of an Orange-Colored Fungus

Maintaining the health of your lemon tree takes a little work.

The lemon tree is a popular backyard plant in the subtropical zones of Florida and Texas and is valued for its fragrance, flowers and fruit. Unfortunately, the heat and humidity of the climates where it thrives also harbor fungi that prey on the lemon tree. Fungal diseases evidenced by reddish-orange and brown blotches--such as greasy spot, alternaria brown spot and melanose--can be controlled by a combination of orchard management, pruning and judicious spraying.

Things You'll Need

• Rake
• Pruning shears
• Tree saw
• Copper fungicide spray
• Bleach and water solution or rubbing alcohol

Instructions

1. Monitor your lemon tree. Know the signs of fungal disease. Greasy spot shows up as yellow to brown blotches on the mature leaves from early summer through early fall. Alternaria brown spot is seen as reddish-brown spots with yellow "halos" on ripening fruit, as well as black lesions on the leaves. Melanose causes unsightly raised lesions on the fruit, leaves and twigs of the lemon tree.

2. Rake up and destroy all leaves and fallen fruit before the rainy season. Mycosphaerella citri, the fungus that causes greasy spot, thrives in the fallen leaves and will infect foliage the following spring.

3. Spray the lemon tree with a copper fungicide early in the season, when leaves are starting to come out, for alternaria brown spot. Spray again when leaves are fully developed, and again approximately four weeks later. Spray every two to four weeks until early summer if it is a particularly wet spring.

4. Spray the lemon tree with a copper fungicide in June for greasy spot, and again three weeks later if the infestation is severe.

5. Install a drip irrigation system. Water from an overhead sprinkler causes the spores of the greasy spot fungus to splash up and infect leaves in the tree above. Splashing water also spreads the spores of Diaporthe citri, the fungus that causes melanose.

6. Prune all dead wood from the lemon tree during its dormant season. Use hand pruners for twigs and small branches. Use a tree saw if large branches are infected. Pruning is especially important for control of melanose. The fungus that causes melanose lives in dead wood, and proper pruning often is enough to control that fungus. Pruning also increases air circulation, which curtails the spread of fungi.

7. Wipe your pruning shears and tree saw with the bleach and water solution or rubbing alcohol between each cut, to avoid spreading the fungus to other branches or trees.

References

• Important Citrus Diseases of Southwest Florida; Dr. Pamela Roberts; University of Florida Institute of Food and Agricultural Sciences
• Citrus Problems in the Home Landscape; University of Florida Extension
• Your Florida Dooryard Citrus Guide; University of Florida Extension