What’s the problem?
My indoor lemon tree has sticky leaves and white spots underneath. What is it?
Diagnosis
The sticky residue and white growths suggest an infestation of mealybugs. Mealybugs are notorious for attacking the fleshy leaves of cacti and succulents, but they also thrive on citrus trees, feeding on sap and weakening the plant. Their waxy coating makes them resistant to standard insecticides, and so difficult to treat. They also excrete honeydew, a sticky substance that attracts fungal growth and can worsen the problem.
Prescription
The first step is to remove mealybugs using a damp cloth or a cotton bud dipped in rubbing alcohol, paying close attention to leaf undersides and stems. Make a spray of neem oil, water, and a few drops of washing up liquid to help suffocate any remaining pests – apply this every five to seven days until the infestation is gone. Introducing biological pest control, such as beneficial nematodes or predatory ladybirds, can also help target mealybug eggs and larvae, reducing the risk of re-infestation. Make sure you check the soil and nearby plants, as mealybugs spread easily and can hide in crevices.
Prevention
Regularly inspect leaves, especially underneath, and wipe them down often to prevent pests from settling. Keep your plant healthy; in bright, indirect light, with good airflow and avoiding overwatering. This should help prevent further attacks.
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