Root damage can kill grapefruit trees. Once you've successfully planted your tree, there's little that can happen to its root system except for root rot. All citrus trees can experience root rot, and the disease can spread from other types of trees to grapefruit and vice versa. Knowing how root-damaging disease occurs and what it looks like can help you keep your orchard healthy.
Grapefruit trees can contract two types of root rot: phytophthora and armillaria root rot. Rainy and warm weather exacerbate the spread of root diseases. Root rot is the major cause of root damage in grapefruit trees.
Both phytophthora and armillaria root rot are causes by fungi, and both can kill the grapefruit tree as they progress. Once one tree is infested, the fungi continue to live in the soil. Fungal spores spread in wet weather, and can infect new trees. Armillaria root rot is caused by the fungus Armillaria mellea; phytophthora root rot is caused by the fungi Phytophthora citrophthora or Phytophthora parasitica.
Above ground, trees with armillaria root rot can develop mushroom clusters in the fall or spring months. Early symptoms include yellowing and dieback of tree leaves. If you pull away the bark from the root, you'll see white stringy fungi called mycelia. Below ground, black fungal bodies called rhizomorphs penetrate the soil and roots near the tree.
Trees with phytophthora root rot also display reduced vigor and dieback of branches. Under ground, the roots rot, turning brown and mushy. The above-ground symptoms of phytophthora can be tricky to distinguish from other plant diseases.
Most cases of root rot end in death for the tree. However, gardeners can attempt to save a tree they suspect has phytophthora root rot by digging up the soil at the base of the tree to expose the roots and allowing the roots to dry out thoroughly. Thereafter they can water the tree less frequently to prevent over-watering. Both types of root rot can also be managed with fungicides, which delay the death of the tree but cannot reverse the root damage.
Prevent root rot by keeping a tree fertilized and inspecting it regularly for changes. Do not plant grapefruit trees in locations where other trees have contracted root rot, since the fungi continue to live in the soil. If you find a tree with root rot, remove it from the ground immediately to prevent other trees from getting infected.