Investigating the Cause of Shoot and Twig Dieback of Clementine, Mandarin and Navel Orange in California crown thinning, gumming on twigs and shoots dieback, and in severe cases, branch dieback of trees (Fig.2). Dieback and staghead are caused by many fungi and a few bacteria that produce … When zinc deficiency is the cause discoloring occurs between distinctly greener veins. Branch canker and dieback can be a serious problem in new plantings; stock sometimes arrives from the nursery with latent infections at the graft union. Trees shed excess fruit they cannot support. Diagnosing Home Citrus Problems AZ1492 April 2009 John Begeman, Glenn Wright PROBLEMS OF FRUIT Fruit Drops Prematurely: Causes: Natural fruit drop occurs during the spring. When the infection kills the graft union, the dead scion retains a dry brown canopy, and shoots … Entire tree. The symptoms produced depend on the variety of plant, environmental conditions, and the virus strain. There are several races or strains of the causal agent. The cause is a bacterium spread by aphidlike psyllids. Click on photos to enlarge Aboveground dieback. Dieback, common symptom or name of disease, especially of woody plants, characterized by progressive death of twigs, branches, shoots, or roots, starting at the tips. These races or strains have varying effects on the many cultivars of citrus. There are a variety of sprays designed to protect citrus trees from Canker infection, such as Liquid Copper Fungicide as a preventative treatment. Symptoms include stunted trees, leaf and fruit drop, twig dieback, and fruit that are lopsided, small and bitter-tasting. IMPACT: The ‘Bingo’ mandarin is a promising citrus variety that many growers have planted, so understanding why the branches of many trees have died in the field is an urgent need. Area(s) affected. Signs/Symptoms. Citrus tristeza virus. The disease can be found in leaves, twigs and fruit of almost any citrus cultivar, causing serious damage to the fruit as well as defoliation and general decline of trees. One or more species of Colletotrichum fungi were associated with twig dieback in ‘Bingo’ mandarin, but demonstrating infection requires more definitive research. The most characteristic symptoms of this disease are the gum pockets which appear on young shoots either Staghead is a slow dieback of the upper branches of a tree; the dead, leafless limbs superficially resemble a stag’s head. Armillaria root rot Identification tip: Pale and wilted foliage, few leaves, and limb dieback are symptoms of Armillaria root rot, dry root rot, Dothiorella gummosis, and Phytophthora root rot.Look for cankers and oozing gum, cut under bark to inspect cambium and wood, and examine roots to help diagnose the cause. Citrus Canker causes necrotic dieback, tree decline, premature fruit drop, and blemished fruit. Excessive twig dieback on the outside of tree canopies may result from a number of factors that cause defoliation including freezes, drought, severe pest pressure, declining diseases such as citrus tristeza virus, blight, water damage, greasy spot, spray burn, or other problems causing severe root damage or leaf drop. The virus can cause the tree to decline, leading to tree death. There are three distinct syndromes of the disease: quick decline, stem pitting, and seedling yellows. C. karstii, a ‘New’ Species Associated With Citrus in California Recent work by researchers at the University of California have now identified C. karstii as a new pathogen of citrus causing twig and shoot dieback with or without gumming and occasionally branch dieback and wood canker in the Central Valley of California.