Vitamin C is an invaluable part of the human diet; without it, our immune systems would be drastically compromised. That's not the only reason for planting your own citrus trees and growing your own fruit, though. Citrus, like other types of fruits and vegetables, always tastes better fresh from the backyard. Like other types of produce, though, citrus is vulnerable to its own kinds of disease and occasionally needs to be nursed through sickness and through health.
Citrus Tristeza Virus
Citrus Tristeza Virus, or CTV, is a viral disease that has, in the past, been responsible for killing millions of orange trees in South America and Africa. The disease has been on record since the late 1800s, and it is only relatively recently that scientists have discovered just what causes it.
The virus is spread in a few select ways: through planting material, through bud wood and by several varieties of aphids, namely, the cotton aphid and the tropical citrus aphid. Since the discovery of these methods of transport, measures have been taken to make sure the virus is not carried to new areas. These methods have been, for the most part, successful, but CTV is still seen.
Signs that the tree is infected can vary based on the type of tree and bud, but generally include stem pitting, yellow leaves, leaves that begin to fold and reduced fruit size. CTV will eventually kill the infected tree.
The citrus nematode is just one of more than 40 different kinds of nematode diseases. Spread by a parasite that attacks roots, a citrus tree infected with citrus nematode can appear healthy for some time after it has been infected. However, the nematode will begin to kill the tree from the root up, and as there is no known cure for the disease, will eventually lead to the tree's death.
Symptoms can take some time to manifest themselves; since citrus nematode has been documented in every citrus-producing region of the world, it's something to stay on the lookout for. Most often, infected trees will begin to produce smaller, irregularly shaped fruits, and less of a crop than in previous years. Yellowing of leaves and the loss of leaves at the top of the trees is also common. Trees may appear healthy for years after infestation, and the only definite way to diagnose citrus nematode is with microscopic examination of root and soil samples.
Black rot can infect both citrus trees and citrus fruits after they have been picked and put in storage. The fungal infection affects mostly lemons and oranges, but has been documented in other citrus fruits.
Infected fruits commonly drop off the tree before other fruits; if there is any question of whether or not a fruit is infected, it should be cut open. The earliest stages of the disease manifests itself in the form of black discolorations at the heart of the fruit, near the area where it was attached to the tree. Black rot spores multiply in wet weather, and if the fruit stays on the tree long enough, it can take on a blackened, mummified appearance.