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White Pine Blister Rust in Illinois

October 27, 1999

We don't see this disease often in Illinois. In fact, it is rare enough that pathologists get excited when they do see it, and it usually means lots of pictures and discussions about the disease. White pine blister rust is a two-host disease requires a Ribes species (currant and gooseberry) and a susceptible pine. In Illinois, you might see this on eastern white pine or possibly limber pine.

Each year, we field telephone questions about white pine blister rust, and usually we convince the callers that the disease is not present. Positive cases have been found in our northern counties. Recently, the disease was found in northern Illinois by one of the State Department of Agriculture inspectors. This situation does not warrant a quarantine, but measures should be taken to control and contain the disease. The high blister-rust hazard areas are in northern climates or high elevation areas where the average temperature is below 70 degrees F. That leaves Illinois fairly safe unless weather patterns change drastically.

From a distance, you notice dead branches, yellowing of foliage on a branch, or poor growth on trees with this disease. Closer inspection reveals resinous cankers at the base of the dead branches. In the spring, you can't miss the yellow blisters that arise from the cankered area. The blistered areas remain, but the yellow color may disappear as spores are released.

This disease usually follows a 3- to 6-year cycle between the pine and the Ribes. Pine needles are infected in the summer and fall, by rust spores on the Ribes. The fungus moves down the pine needles and into the stems where it goes through various growth stages. Eventually (two or three years later) in the spring, rust spores are ready to move back to the susceptible Ribes plants. This does not prevent the rust fungus from continuing to develop on the pine. The fungus usually moves only a few hundred meters. If it does not reach an alternate host, the cycle will stop.

Most biology students have heard about the removal of Ribes species to control this disease. That eradication program was abandoned because it did not work in areas of high risk, and it was not necessary elsewhere. Should you find yourself dealing with this disease, prune out diseased limbs, prune out lower limbs on young trees to prevent trunk infection that would kill the tree, and consult with university specialists. There are no chemicals that we can recommend in Illinois. Bruce Paulsrud, pesticide applicator training pathology specialist, found these web sites that might also be helpful.

Cornell has a Christmas tree IPM site that covers blister rust at http://ppathw3.cals.cornell.edu/Trees/WPBRust.html

Minnesota's web site discusses the disease at http://www.mes.umn.edu/Documents/D/G/DG6659.html#pine

This disease is not a major problem in Illinois, and we do not have a fact sheet discussing this topic. Clear photographs of the disease can be found in Diseases of Trees and Shrubs by Sinclair, Lyon, and Johnson, published by Cornell University.

Author: Nancy Pataky


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