Quince trees seem to be one of the least common fruit trees in Seattle, and Western Washington in general. This is unfortunate because they can be made into some delicious jams and sauces. If you’re fortunate enough to have a quince tree in your yard, there’s a chance your tree has quince leaf blight. This is a fungal infection (like nearly all leaf blights) that shows up as brown spots on the leaves and sometimes the fruit.
The PNW Plant Disease Handbook from Oregon State University sums up the life-cycle: “The fungus overwinters in diseased leaves and shoots. Cool, wet weather favors disease development in the spring. Spores are disseminated by splashing water and need 8 to 12 hours of leaf wetness to infect leaves. Susceptibility does not seem to be reduced with leaf maturity.”
The fungus (Diplocarpon mespili) can infect other members of the Roseaceae family such as Asian pears, hawthorn, pear, photinia and serviceberry, but the symptoms are usually not as severe.
Like most fungal infections keeping the orchard tidy is one of the best ways to keep the disease in check. Raking up and disposing (not composting) the fallen leaves and any infected branch tips or fruit will reduce the re-infection rates the next spring. Don’t irrigate with overhead sprinklers because the fungus needs water to infect leaves. A copper based fungicide may speed recovery, but often good orchard hygiene will keep the disease in check.
-Pscheidt, J.W., and Ocamb, C.M., senior editors. 2014. Pacific Northwest Plant Disease Management Handbook [online]. Corvallis, OR: Oregon State University. http://pnwhandbooks.org/plantdisease (accessed 22 Sept. 2014).
-Ashridge Nurseries, http://www.ashridgetrees.co.uk/hedging-trees-fruit-questions/hedging-fruit-tree-diseases/quince-leaf-blight. (accessed 22 Sept. 2014)