Problems with lemon tree fruit dying early are a result of pests and diseases. From fungal infections to insect pests, when a lemon tree is under attack, it becomes unhealthy and shows symptoms of illness, including prematurely falling from the tree or rotting on the branch. Keep your lemon tree vigorous for better resistance to illness.
Anthracnose is a fungal infection caused by the fungus Colletotrichum gloeosporioides that presents a problem with lemon trees causing early of fruit, according to the Purdue University Cooperative Extension. Displaying itself through symptoms including leaf drop, dieback of twigs and dark spots on twigs and leaves caused by the fungal spores, anthracnose also attacks the fruit of the lemon tree, explains the University of California IPM Online (reference 5). The rind starts to display spots and streaks that stain the fruit. Anthracnose in lemons can lead to fruit drop, fruit decay and death. For control, apply the fungicide azoxystrobin or zinc sulfate/copper sulfate/hydrated lime to the entire tree if the problem is severe.
Citrus scab (such as Elsinoe fawcetti) causes health problems in lemon trees causing early death of fruit. Citrus scab displays symptoms on lemon trees including raised, round spots on both fruit and leaves; occasionally, the other side of the leaf will display a depression, according to the University of Florida IFAS Extension. Extreme infection causes deformation and death of lemon fruit. As a chemical control, apply three treatments of copper fungicide according to the following schedule: first at approximately 25 percent of "spring flush leaves", apply again when petals begin to fall and apply the final application three weeks after the second treatment.
Problems with lemon tree fruit dying early often include the presence of a disease called botrytis. Disease develops from the fungus Botrytis cinerea, most often encouraged by periods of excessive humidity paired with cooler temperatures. Carried by spores, botrytis forms a "gray mold" on infected fruit. Affected fruit may become completely covered in what looks like gray velvet and will eventually die. For control, keep lemon trees vigorous and wound-free. Apply fungicidal treatments including copper and benzimidazole before periods of extreme moisture, as directed by the University of California IPM Online.