Disease pathogens caused by fungi often make their way into orchards or onto residential properties. Fungi attack citrus plants, causing mild to severe infections. Identifying preventive methods as well as symptoms to look for will assist you in keeping your citrus plants free of fungi that cause problems like decay or the incidence of abnormal growths on plants.
Affected Citrus Plants
Though orange trees often come to mind when we think of citrus plants, other plants affected by citrus fungal infections include grapefruit, mandarins, tangelos, limes, lemons, kumquats and limequats. Determine the type of plant or tree growing in your garden for appropriate diagnosis and disease control, particularly if you decide to apply a fungicide.
Fungal Diseases and Symptoms
Many different fungal diseases affect citrus plants. Foot rot is a soil-borne disease, also known as Phytophthora foot rot or Phytophthora gummosis. It is caused by the fungus Phytophthora parasitica as well as Phytophthora citrophthora. This fungal infection causes gumming and yellowing of foliage, according to the University of Arizona Extension Plant Pathology. Melanose, caused by the fungus Diaporthe citri Wolf, affects citrus plants and causes small water-saturated spots on leaves. The spots dip in the center and have a yellow border, and the leaves secrete a gumlike substance. Once the substance dries, the leaves feel rough and may appear malformed, according to the University of Florida IFAS Extension. Greasy spot is also a fungal infection of citrus plants; it is caused by Mycosphaerella citri Whiteside. Lemons and tangelo fruit plants are the most vulnerable. Greasy spot causes an uneven yellow appearance underneath leaves with blistered spots and yellow/brown spots. Spots present on fallen leaves often resemble grease.
Phytophthora foot rot damage includes severe thinning of tree foliage, rotting of wood near the base of the tree and decayed roots and may result in tree death. Citrus trees affected by melanose infection may suffer from defoliation or branch dieback. Greasy spot has the potential to result in severe defoliation during the autumn and winter seasons. Fungal infections significantly reduce tree health.
Natural Control Through Proper Care
Vigorous, healthy trees are much less susceptible to the incidence of fungus on citrus because they are capable of fighting off infection. Maintain your citrus plants according to their particular needs for consistent growth. All citrus plants thrive in full sunlight and will suffer from diminished health if grown in shaded areas. Citrus prefers moist, well-drained soil. Keep citrus plants out of wet sites and water-logged soil, as the trees absorb water quickly; overwatering trees results in fruit split and conditions in which your tree will not receive adequate nutrition. If drainage is an issue, consider planting on a raised bed. Collect, remove and destroy any affected plant parts to prevent spread of infection. Sanitize pruning tools between cuts and from plant to plant to prevent transfer of fungi. Avoid creating wounds in trees, as fungi often enter through open lesions.
For chemical control, apply the fungicide cupric hydroxide on tree wounds. If foot rot is present, apply fosetyl-Al four times annually, or apply a treatment of metalaxyl. For melanose, use a copper-based fungicide like copper sulfate applied up to three weeks after flowering with a follow-up application after four weeks. If greasy spot is a problem, apply benomyl once during June or July, or apply cupric hydroxide once before and after flowering, as directed by the Texas Cooperative Extension Service.