Submitted to: California Citrus Production Manual
Publication Type: Book / Chapter
Publication Acceptance Date: 5/1/2010
Publication Date: N/A
Technical Abstract: There are some disorders of citrus that are not currently known to be caused by a pathogenic agent, but appears to be inherited, physiologically based, or caused by environmental conditions. Environmental injuries include heat injury and sunburn; wind injury; smog; flooding; hail damage; lightning; and cold damage. Cold damage is discussed in another chapter. Heat and sun damage may cause misshapen fruit, abnormal coloring of the skin, burning of the albedo, drying and damage to the pulp, and seed abortion. There is also vegetative damage caused by high temperatures. Wind injury is often associated with water stress but can also damage leaves mechanically. Flooding causes damage via the creation of anaerobic conditions in the soil, which can result in necrosis of root tissues. It is not common in California. Hail and lightning damage is also not common in California but the former may cause mechanical damage to leaves and fruit and the latter can damage localized areas of the tree. Water stress is unusual in well-managed orchards but may sometimes appear. In extreme cases, the symptoms include wilting of young leaves and fruit dehydration. Under conditions where the leaves cannot obtain enough moisture, mesophyll collapse can occur, and in some cases, twig tieback. Cultural injuries include those caused by chemicals and those caused by equipment. With regard to chemicals, the most common injuries occur due to herbicide drift. Equipment injuries include root pruning and other mechanical damage caused by farm equipment. The only significant genetic disorder of citrus is "wood pocket". This is a problem mostly with large-fruited acid limes, which are not widely cultivated in California. Trees with wood pocket develop small lesions in the bark, which eventually turn into areas of dead, fissured wood. The wood beneath the fissures is discolored and filled with gum. Affected branches lose their leaves and die back. Eventually, the entire tree may die. Fruit and leaves of wood pocket-affected trees show variegation or sectorial striping. Symptoms of wood pocket develop between 3 and 20 years of age. Heat increases the speed of symptom development and also the possibility of tree death. Management is via the use of a wood pocket-free budline recently released in California.