Galls up to 2 inches in diameter appear on the tree. For growing olive trees in pots, choose the ‘Amygdalolia’ variety, which naturally grows to smaller sizes. The French agriculture ministry announced the discovery of … Every tree has the future potential for disease and insect damage. Olive knot disease on olive, Olea europaea, is distributed in olive-growing regions worldwide, and reports of the disease in California date back to the late 19th century.The disease is caused by Pseudomonas savastanoi pv.savastanoi (Psv), a bacterial pathogen that is spread short distances during the winter and spring rain events associated with California's Mediterranean climate. Factors such as location and weather will play a part in which issues your tree encounters. Keeping olive trees well-fed and adequately watered is the best initial defence against pests and diseases, since vigorous trees are better able to withstand attack and less likely to suffer long-term damage. Around the Mediterranean Sea the major pests is the medfly, the olive fruit fly [Dacus oleae]. Infections usually occur during cooler spring or summer months, and the pathogens are easily spread by water. We give a basic description of the disease and the damage it causes and give you a link to the UC Integrated Pest Management (UC IPM) page on the subject for more details and for treatment options and risks. Olive knot is a bacterial disease that is spread by water and enters the tree through pruning cuts, cracks or wounds on the tree. This disease causes leaves to turn brown. Southern Europe Could Lose $22 Billion Fighting Deadly Olive Tree Disease The tree killer is a bacterium called xylella fastidiosa. This olive tree disease typically defoliates and kills the affected foliage. Verticillium wilt affects olive trees in commercial and landscape plantings and many other species. Diseases & parasites that attack olive tree. Pest & Disease Control for Olive Trees. A deadly disease estimated to have killed a million olive trees in Italy has spread to France.. Nonetheless, some parasites are common and it is worth treating them so as to not weaken the olive tree. Further afield, even more groves show the tell-tale signs: dying leaves and branches. (Photo by Cain Burdeau) Along the high­way, tow­er­ing olive trees are cov­ered in brown brit­tle leaves. Olive Agriculture: Pest Management Guidelines University of California's official guidelines for pest monitoring techniques, pesticides, and nonpesticide alternatives for managing pests in agriculture. Pests & Diseases of Olive Trees The olive tree is affected by some pests and diseases, although it has fewer problems than most fruit trees. Olive tree near Oria, in the area of Salento in Puglia, that has been felled due to an outbreak of Xylella fastidiosa. 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