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Syringe Injection of Water into the Trunk: A Rapid Diagnostic Test for Citrus Blight. R. F. Lee, Associate Professor, University of Florida, Citrus Research and Education Center (CREC), Lake Alfred 33850. L. J. Marais, Senior Research Pathologist, Outspan Citrus Centre, Nelspruit, South Africa; and L. W. Timmer, Professor, and J. H. Graham, Assistant Professor, University of Florida, CREC, Lake Alfred 33850. Plant Dis. 68:511-513. Accepted for publication 27 December 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-511.

A diagnostic test for citrus blight is described in which a 30-ml plastic syringe was used to inject water under pressure through a hole drilled in the trunk of the tree. About 1 ml/sec could be forced into healthy trees, but little or no water could be injected into blighted trees. In Florida and South Africa, water uptake in blight-affected trees as measured by the syringe test or the standard gravity injection method declined with the negative logarithm of the canopy symptom rating. Zinc content of trunk wood, another indicator of blight, increased as a power function of the canopy symptom rating. Visual diagnosis, the gravity injection test, the syringe test, and diagnosis by zinc content concurred in the majority of the cases, but the gravity injection test appeared to be the least reliable. The syringe injection test is simple, fast, requires less equipment, and is at least as accurate as presently available diagnostic techniques for blight.