Olive leaf spot is a fungal disease which is found around the Mediterranean and in Eritrea, South Africa, California, Argentine and Chile. The fungus infects the leaves, severe attacks resulting in partial to complete defoliation of the tree, which seriously reduces the crop in the following season. Olive knot is a bacterial disease which occurs in the Mediterranean region, in California and Argentina. The disease causes knots to develop on the young shoots which eventually kill the shoots. The bacteria can also infect the leaves, causing premature leaf drop.