Grapefruit trees reach a height of up to 30 feet with 5-inch-long leaves. The evergreen foliage lives for approximately two years before it is shed and replaced by new leaves. All cultivars have seeds--50 to 60 per fruit. A member of the citrus family, the grapefruit tree suffers from several diseases.
Fungal and Viral Diseases
Four fungal diseases afflict the grapefruit tree. Melanose, greasy spot and citrus scab occur on the foliage of the tree. The fungal infection foot rot affects the tree's root system. Viral diseases can also appear on the grapefruit. Fungal infections can be treated, but when a grapefruit tree has a viral infection, it will slowly die over time and cannot be cured, according to the University of Florida.
Greasy spot appears on the leaves of the grapefruit tree as tiny black spots that look similar to grease. Melanose forms raised, brown spots on the leaves. The spots feel rough to the touch. The spots also appear on the fruit of the tree. Citrus scab forms large bumps on the branches, leaves and fruit of the tree. The leaves and young stems of the citrus tree contort and are stunted. Foot rot causes lesions at the base of the tree's trunk. Bark scaling is common if the tree is afflicted with a viral infection.
Greasy spot occurs when the fallen grapefruit leaves are allowed to lay on the ground beneath the tree and form fungus. Melanose occurs when the tree sustains overhead watering and has an abundance of dead twigs which produce inoculum. The combination of the water and inoculum make an ideal breeding ground for the fungus. Citrus scab occurs when there is an ample amount of spring rain fall in cool weather. Grapefruit trees in soil that does not drain well often suffer from foot rot.
To treat foot rot, carve away the infected tissue at the base of the tree and paint it with a tree sealant or copper paint. You should also apply a systemic fungicide. Pruning away lower branches to increase air circulation can help rid the soil of moisture which breeds the fungus. Melanose does not kill the tree but can be controlled by pruning away dead twigs and limiting overhead irrigation. Copper sprays work to treat citrus scab, melanose and greasy spot.
Prevent fungal and viral infections by maintaining the grapefruit tree's health. Fertilize the tree and prune away any dead or damaged wood. Remove all fallen leaves from the base of the tree. Keep mulch at least 1 foot away from the tree's trunk to help prevent fungus from occurring, advises Texas A&M University. Take care when cultivating around the tree's base so that the bark is not damaged. Avoid using overhead irrigation systems. The grapefruit tree appreciates a slow trickle irrigation at its base.