How To Treat Greasy Spot On Lemon Tree

Lemon trees can be prone to developing a condition known as greasy spot. This fungal condition is caused by a type of fungi known as Phyllosticta citricarpa. It can cause yellow spots beneath the leaves of affected trees and causes defoliation. Greasy spot can weaken a lemon tree, causing it to produce fewer fruits and suffer from stunted growth. Fortunately, there are ways to treat it effectively.

The first step of treating greasy spot is to remove any fallen leaves from the ground around the lemon tree. This should be done at least once every week during the trees’ growing season, as the fungi from these leaves can spread and cause more infection. Seeking out any newly developed yellowing of leaves, as this could be an early sign of infection, may also be done at this time.

Chemical sprays may be employed on the lemon tree in order to inhibit the growth of the fungi causing greasy spot. These sprays come in varying strengths and are typically applied at least two times during the growing season. Caution must be taken when spraying the tree, as it is easy to cause overexposure and damage to the plant. It may be beneficial to consult with a certified arborist to ensure proper application.

Encouraging good air circulation around the tree can also be helpful in preventing the spread of greasy spot fungi. Pruning back limbs and removing low-hanging branches can help to maintain airflow around the tree and make it harder for fungi to spread. Leaf spacing can also be adjusted to increase airflow and provide the tree with more sunlight.

In some cases, a natural remedy can be applied. Neem oil is a naturally-occurring biopesticide that can be used to fight the greasy spot fungi. It should be mixed according to the instructions provided on the product label and used every 5-6 weeks during the growing season. Neem oil is safe to use, with very few side effects for the environment or nearby animals.

Chemical fertilizers, such as ammonium sulfate, can be applied if the tree is found to be nutrient deficient. The recommended usages will vary by manufacturer and concentration; however, usual recommendation is to apply a nitrogen-rich fertilizer every 3-4 months. Monitoring and adjusting as needed, according to a soil test result, can help to guarantee proper nutrition and tree health.

Applying mulch to the base of the tree can also be beneficial. Mulch can help to prevent the splashback of fungi-carrying water and should be applied near the base of the trunk. A recommended depth is 2-3 inches, avoiding contact with the trunk itself.

Natural Remedies

Using natural remedies such as Neem oil to treat greasy spot can be beneficial in a number of ways. Not only is it an effective fungicide, it is non-toxic and can help to improve the overall health of the tree. Neem oil is best used as a preventative measure, to ward off potential infection, rather than when the infection has already taken hold. As such, it should be used as soon as possible and implemented regularly throughout the growing cycle.

Another natural remedy known to be effective is baking soda. This remedy should be applied soon after a spread of greasy spot is witnessed. It is important to apply the baking soda directly on the trees’ foliage, as the fungi can be found on the leaves. Spraying the baking soda 3-4 times weekly, for a total of four weeks, can help to eliminate the spread of the fungi.

The most important factor when utilizing natural remedies is to ensure that the proper dosage is being maintained. If an inadequate amount is used, it is unlikely to be effective. Before using any natural remedy, it is important to consult with a certified arborist who can advise on the best means of treating the lemon tree.

Finally, it is important to note that natural remedies may take longer than chemical ones to take effect and may require frequent treatment. Although they are generally considered safer to use and are better for the environment, natural remedies, such as Neem oil, may be less effective at eliminating the greasy spot fungi. This may result in having to employ a combination of natural and chemical remedies.

Environmental Conditions

Environmental conditions can be a contributing factor in the growth and spread of greasy spot fungi. Poor drainage, high humidity, and minimal airflow can all work together to create conditions in which the fungi can thrive. As such, it is important to ensure that the lemon tree is located in an area with adequate drainage and air circulation.

Allowing more sunlight to reach the tree is another effective way of preventing the spread of greasy spot fungi. If the tree is unable to absorb a sufficient amount of sunlight, it can become weakened and prone to disease. It is recommended to prune any overhanging branches and limbs to promote increased airflow as well as better access to natural light.

Finally, it is important to remain vigilant and inspect the tree regularly. Allowing small amounts of greasy spot to remain on the leaves can create a higher risk of further spread and infection. Remove any affected leaves immediately and dispose of them in a sealed bag. Monitor the tree closely, checking the underside of leaves weekly, and take action accordingly.

Sanitation Practices

Sanitation practices are key in protecting the lemon tree against infection. As fungi and pathogens can be spread by hand, it is important that hands and tools are regularly cleaned and washed. This can be done by using warm soapy water, followed with a bleach solution. All tools should also be sterilized before using them on unaffected areas, eliminating the possibility of spreading existing infections.

It is also important to keep all areas around the tree clear and free of debris. Fallen leaves and other decaying material can provide an ideal place for the fungi to incubate and spread further. It is recommended to clear these areas at least once every week and clearing all diseased material as soon as it is identified.

Sanitation practices are particularly important if multiple lemon trees are in the same vicinity and one is found to have an infection. In this case, it is crucial to prevent the spread of the infection to other trees and only use untouched tools on other trees. As the infection is likely to return, it is important to maintain a routine of disinfection and debris removal.

The Benefits of Prevention

The best way to deal with greasy spot on the lemon tree is to prevent it altogether. Sanitation practices, coupled with regular pruning and an appropriate location, can go a long way in making sure that the tree remains fungus-free. This is particularly true when caring for a lemon tree as a part of a larger orchard, as preventing the spread of infection is essential in protecting other trees.

Also, by ensuring that the lemon tree has the adequate nutrients it needs to grow and thrive, it will be less likely to become infected by fungi. Proper fertilization and soil management is key, as the tree needs to have strong defenses against infection. Nutrient testing and regular application of appropriate fertilizers can make a huge difference in maintaining a healthy tree.

Finally, avoiding overwatering can help to reduce the chances of an infection. Overwatering can force the roots to stay in a damp environment, giving the fungi an ideal habitat. Monitoring the soil around the tree can help to identify when the tree may be receiving too much water and when to adjust watering frequency.


Affected by greasy spot, a lemon tree may suffer from defoliation, stunted growth, and fewer fruits. It is important to take steps to protect the tree and prevent the spread of infection. Chemical sprays and natural remedies can be deployed, although it is best to consult with an arborist before doing so. Additionally, good environmental and sanitation practices can go a long way in keeping the tree healthy and free of disease.

Gordon Wesson is an environmentalist and author who lives in the Pacific Northwest. He has been writing for many years about topics related to trees, the environment, and sustainability. In particular, he is passionate about educating people on the importance of living in harmony with the environment and preserving natural spaces. He often speaks at conferences and events around the country to share his knowledge with others. His dedication to protecting our planet makes him one of the leading voices in his field today.

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