Citrus Phytophthora

PhytophthoraLeaf: Yellow foliage and shoot die-back. If citrus weevils are present adults may feed on leaves causing notching.

Trunk: Infection of the trunk by Phytophthora results in dark water soaked areas in the area of active infection. Lesions usually occur on the bark or at the bud union. Lesions may exude copious amount of gum and a brown necrotic area will be found under the bark lesions. Dead bark tends to break away from the trunk in vertical strips. Lesions may spread around the circumference of the trunk slowly girdling the tree.

Serrano, D., Serrano, E., Dewdney, M., and Southwick, C. (2010). Citrus Diseases. USDA/APHIS/PPQ Center for Plant Health Science and Technology. [09-14]

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Citrus Nutrient Deficiency

nutrient-deficiencyNutrient deficiencies have a wide range of symptoms that will not be fully covered in this key. Things to look for are how symptoms are distributed throughout the tree and throughout the grove. Nutrient deficiencies tend to be more uniformly distributed in the tree than the diseases they are commonly confused with. A nutrient deficiency may express itself on the whole tree level causing twig die-back, long thin branches, yellowing, and reduced or abnormal growth. Nutrient deficiencies may alter fruit characteristics such as shape, hardness, peel thickness, and peel texture. Nutrient deficiencies may manifest on leaves resulting in chlorosis, enlarged or shrunken leaves, raised veins, unusual leaf patterns and changes in leaf coloration. For example, zinc deficiency will appear on new foliage throughout the tree in contrast to early HLB symptoms which are restricted to a single or a few shoots.

Serrano, D., Serrano, E., Dewdney, M., and Southwick, C. (2010). Citrus Diseases. USDA/APHIS/PPQ Center for Plant Health Science and Technology. [09-14]

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Citrus Melanose

MelanoseAbout one week after infection foliar symptoms appear as small brown discrete spots. These spots become impregnated with a reddish-brown gum and are raised above the leaf surface. Early pustules on leaves are surrounded by a yellow halo. However, this halo quickly disappears leaving only small corky pustules. The numerous small pustules give the leaf a rough sandpaper texture. Distortion and dieback of young shoots are associated with severe infections.

Serrano, D., Serrano, E., Dewdney, M., and Southwick, C. (2010). Citrus Diseases. USDA/APHIS/PPQ Center for Plant Health Science and Technology. [09-14]

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Citrus Leprosis

LeprosisFoliar lesions are shallow but visible on both sides. Each lesion is produced in association with the feeding by the mite vector. Symptoms appear 1-2 months after inoculation. Typical lesions are circular with a dark-brown central mite feeding spot. The overall lesion size may vary from 10-30 mm with the central mite feeding spot ranging 2-3 mm in diameters. The feeding spot is surrounded by a chlorotic halo with 1 -3 concentric rings. Lesions may coalesce to form larger erratically shaped lesions. Under high temperature conditions the center of the lesion may crack.

Serrano, D., Serrano, E., Dewdney, M., and Southwick, C. (2010). Citrus Diseases. USDA/APHIS/PPQ Center for Plant Health Science and Technology. [09-14]

Read more ...