Quince Rust is caused by the fungus Gymnosporangium clavipes. Fruits in the pome fruit group (apples, quince, pear and mayhaw) are susceptible. A unique aspect of this disease is that the eastern red cedar and some junipers are essential for the continuation of the disease from year to year. The fungus completes part of its life cycle on the cedar and junipers and part on the mayhaw.
In mayhaw the fruit is affected and on cedar trees cankers are formed on the twigs, limbs, or trunk.The mayhaw fruit infected with the fungus will look spiny with a coating of orange powdery fungal spores.The mayhaw fruit is susceptible to infection by the fungus as the blossoms open and until shortly after petal-fall.The correct temperature and moisture for the fungal spores to germinate and infect the blossoms must occur for there to be an infection.
Management of quince rust would start with planting a selection of mayhaw that has resistance to the disease if available. If you already planted a susceptible selection, then the elimination of cedar and junipers close to the mayhaw would reduce the number of fungal spores that could cause an infection. This may not be very practical.A fungicide application from the time the flower buds begin showing color through bloom would help manage the disease. Fungicides available for homeowners are sulfur or myclobutanil. Copper fungicides may be used but not during bloom. For more information on fungicides for homeowners click here.
For fungicides for commercial growers click here.
Read the product label to make sure the product is labeled for quince rust and can be applied on mayhaw. Follow the mixing instructions and the pre-harvest interval.
For more information on controlling plant diseases call your local Extension Office or refer to the Louisiana Plant Disease Management Guide located on the LSU AgCenter’s web site here. Remember to always read and follow the product label directions before making a pesticide application.
The LSU AgCenter and the LSU College of Agriculture