CITRUS DISEASES

Citrus Diseases

Citrus Pathology Program
Graft transmissible pathogens such as the citrus tristeza virus (CTV), citrus viroids, tatterleaf virus (CTLV) and psorosis virus are major concerns to the Texas Citrus Industry.
Size: 2.3 K

Citrus - Black Rot
The infection starts while the fruit is still on the tree. The fruit is infected through cracks or openings on the stylar end of fruit. The fruit colors prematurely and drops.

Citrus - Brown Rot
The same species of Phytophthora that causes foot rot can infect fruit, commonly those close to the ground. Fruit are infected during periods of excessive rain, resulting in decayed areas that are brown, firm and leathery.

Citrus - Cachexia
This pathogen makes the inner bark surface bumpy. The bark projections are smooth, in contrast to the sharp projections produced by the citrus tristeza virus.
Size:1.3 K

Citrus - Diplodia Stem-End Rot
Fruit are contaminated with the fungus in the field, but the disease commonly occurs at the packing house or in transit. Decay occurs around the stem end and advances in streaks down the side of the fruit.
Size: 1.9 K

Citrus - Exocortis
This pathogen causes bark-shelling and stunting of trees on trifoliate orange, trifoliate hybrids, and Rangpur lime rootstocks. Sour orange rootstock is tolerant.

Citrus Feeder Root Rot
The fungus infects the cortex of feeder roots, giving the root system a stringy appearance. This can lead to yield loss and a general prolonged tree decline.
Size: 1.2 K

Citrus Firing
The injury is usually limited to late growth flush (September or October) which has not matured prior to the arrival of a dry cool front in October or November.
Size: 1.2 K

Citrus - Flyspeck
This is caused by a fungus that keeps citrus fruit from turning yellow in the infected spots. Small black specks are formed on the rind in areas immediately surrounding the oil glands.
Size: 1.3 K

Citrus - Greasy Spot
This is a very common disease in Texas. The fungus is primarily a leaf pathogen, but it can also infect fruit. Yellow spots are seen at first on the upper surface of the leaf.
Size:2.2 K

Citrus - Green Mold
The fungus causes a rapid breakdown of fruit punctured or bruised during harvesting and packing operations. The fungus enters the fruit only through wounds.

Citrus - Heart Rot
The visible external symptom is the fruiting structures ("conks") of the fungus projecting from the trunk.

Citrus - Melanose
This is primarily a disease of grapefruit. The first symptoms on leaves are small, circular, dark depressions with a yellow margin.

Citrus - Oleocellosis
The damage is caused to rind cells by peel oil release as a result of abrasion, rough handling or other injuries. Foggy and wet weather predispose rind to oleocellosis by making the fruit more turgid.

Citrus - Phytophthora Foot Rot
This is one of the more important pathogens of citrus in Texas.

Citrus - Rio Grande Gummosis
This is not a common disease. Narrow cracks appear in the bark which exude a pale yellow gum. Symptoms are usually found in association with injured or dead branches.
Size: 1.5 K

Citrus - Scally Bark
Sweet orange, grapefruit, and tangerine are severely affected. The pathogen is spread by budding nursery stock with budwood from infected trees.
Size: 1.6 K

Citrus - Slow Decline
The nematode causing this disease attacks the roots. Symptoms associated with the presence of nematodes are wilting, lack of vigor, poor fruit production, small fruit size, and poor response to watering and fertilization.
Size: 2.2 K

Citrus - Tatter Leaf
This virus causes a bud union crease. It can be detected using certain indicator plants (e.g. swingle citromelo citrus). It is serious on rootstocks of Troyer and Carrizo.
Size: 1.3 K

Citrus - Leaf Miner
The larvae tunnel within the leaf, leaving snaking trails of dead tissue.
Size:1.1 K

Citrus - Leaf Yellowing
Injury by the herbicides Krovar (a mixture of diuron and bromacil) or Hyvar (bromacil) can cause yellowing.
Size: - 1.8 K

Complete Description of Citrus Diseases

Diseases Affecting Fruit
Diseases that primarily affect citrus fruit are usually of most concern to handlers and shippers. Many, however, begin in the orchard and can be reduced if proper measures are taken.
Author: Jose M. Amador

Diseases Affecting Localized Parts of Trees - Part 1
Author: Jose M. Amador

Diseases Affecting Localized Parts of Trees - Part 2
Author: Jose M. Amador

Disease Management
If a plant pathogen is present in an orchard, the severity of the disease it causes will be determined by the level of infestation, by environmental conditions, and the susceptibility of the plant, which, in turn, is determined by its genetic characteristics.
Author: Thomas Isakeit

Fungal Diseases and Nematodes
Citrus diseases affecting the entire tree can be classified into two general categories: parasitic and nonparasitic. Parasitic diseases are caused by fungi, bacteria, viruses and nematodes.
Author: Jose M. Amador

Individual Citrus Diseases
Submitted: 01/01

Viral Diseases
Four virus diseases which occur on citrus in the Lower Rio Grande Valley are exocortis, xyloporosis, tristeza and psorosis. The first three cause rootstock diseases, but psorosis causes bark shelling on the trunk and branches of trees older than 8 to 10 years.
Author: Jose M. Amador