Huanglongbing (Citrus Greening)

HuanglongbingAlthough symptoms differ according to citrus variety, common symptoms may be described. The most characteristic symptom of HLB is a blotchy mottle. This mottling is distinct from nutrient deficiency in that HLB induced mottling usually crosses the veins and is asymmetrically displayed on the leaf blade. Mottling is most frequently found on newly mature hardened-off leaves but fades with leaf age. The blotchy mottle will be visible on both sides of the leaf and have multiple hues of yellow and green. Dark green areas can sometimes be reduced to small circular dark green dots that contrast with the light yellow/green background. This symptom is referred to as green islands and had been occasionally observed on sweet orange. In addition to blotchy mottle, infected leaves may be thicker and leathery and have raised corky veins. It is common to observe foliar symptoms that resemble nutrient deficiency similar to zinc patterned deficiency. A tree affected by HLB may exhibit yellow shoots and or deficiency symptoms that are on one or many branches randomly arranged in the canopy. This contrasts with a true nutrition deficiency that is exhibited uniformly throughout the canopy. On severely infected branches leaves may form "rabbit ears" that are small upright shoots with compressed internodes.

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 Greasy Spot

Greasy-spotFoliar symptoms first appear as yellow spots on the upper leaf surface, with a corresponding slightly raised, pale orange to yellowish brown blister on the lower surface. Later the symptoms on both surfaces become darker brown or black and show a more 'greasy' appearance.

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 Variegated Chlorosis (CVC)

citrus-variegated-chlorosisFoliar symptoms of CVC are very similar to nutrient deficiency and other diseases; therefore, it is difficult to rely on foliar symptoms alone for identification. Early leaf symptoms resemble zinc deficiency with interveinal chlorotic areas on the upper surface. Early symptoms may be limited to a single branch. As the leaf matures, gummylesions become visible on the lower leaf surface corresponding to chlorotic areas on the upper surface of the leaf. The chlorotic areas gradually enlarge toward the leaf margin, and the lesions on the underside of the leaf may become dark brown or necrotic. Leaves may be smaller than normal. Leaf symptoms are most pronounced on mature leaves (behind the new flush).

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 Stubborn Disease (CSD)

citrus-stubborn-diseaseSymptoms can vary with season and variety but typically include small size with upright position; some mottling resembling nutritional deficiencies; shortened stem internodes leading to bunchy-type growth. Symptoms on mildly-infected trees are often localized within a sector of a 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]

Read more ...