Scorch

Related links............... Cultivation; Cultural Problems

SCORCH was a disease of unknown origin that makes an iris extremely sick. Generally the first apparent symptom is the brownish-yellow color of the center leaf in the fan. If this leaf resists being pulled out and the scorched appearance spreads to adjacent leaves, chances are that the plant has scorch. If the scorched plant is dug, the root system will appear to have disintegrated. Scorch occurs most often after mild winters in cold climates. It seems to be the result of stress that occurs when plants grow when they shouldn't.

There are few preventative measures and no known measure is fully certain. In cold climates, mulch to keep the soil around the roots frozen during winter thaws. Time the application of fertilizer so that it is available to the iris during its maximum growth periods rather than when the plant should be dormant.

In a 1971 publication that was not well known, Scorch Disease of Rhizomatous Iris by J. C. Bald implicated the Pseudomonas bacterium which causes scale tip rot of lilies. More recent work did not support the earlier conclusion: Pathogenicity of Pseudomonas gladioli pv. gladioli on Rhizomatous Iris and Its Possible Role in Iris Scorch by A. I. Wrobel, J. E. Watkins, and D. H. Steinegger, 1992. More recently Evidence seems to point to a phytoplasma ( a bacterium without a cell wall. ) Since these are extremely hard to culture living only within cells or insect vectors the specific strain may yet to be identified. Unfortunately no study specific to Iris was found in a Google search. Some strains are treatable with tetracycline but this may be illegal in some regions and effectiveness has not been verified. It has been suggested that like certain viruses heat may be able to kill the pathogen but there may be a fine fine between killing the disease and killing the subject.

The best practice is to immediately isolate the infected parts and destroy them before they can be spread to healthy portions of the plant.

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-- Main.RPries - 2010-10-13