The leaf blight disease of almond and its control

Leaf blight occurs in the Sacramento Valley and in the northern part of the San Joaquin Valley on most varieties of almonds. This disease has not been reported from any other part of the world. On highly susceptible varieties (Drake, Ne Plus Ultra, and Peerless) 15 to 20 per cent of the leaves may he destroyed during the growing season. An immediate reduction in productivity, however, results from the loss of leaf and flower buds, which are killed by the extension of the causal fungus (Hendersonia rubi Sacc.) from the base of the leaf petiole into the supporting twig. Leaf blight is identified by the sudden wilting and dying of leaves throughout the summer. Although a few affected leaves fall, most do not. Fragments of the petioles remain on the tree and produce conidia the following winter and spring. The conidia of the fungus are shaped much like conidia of Coryneum beijerinckii Oud. (cause of the Coryneum hlight of almond) but are much smaller.

Control may be obtained by spraying trees with either an eradicarive or a protective fungicide. The eradicative fungicide, sodium pentachlorophcnoxide, applied in spring just before the buds begin to open is effective against both leaf blight and the brown-rot blossom blight disease caused by Sclerotinia laxa. N-phenylmercuriethylenediamine is also an effective eradicarive fungicide against the leaf blight fungus. Protective fungicides (capran, ziram, and dichlone) applied at the petalfall stage of bloom, as recommended for the control of Coryneum blight, also reduce infection by the leaf blight fungus.