Brown Rot (fungus – Monilinia sp.): Only the blossom blight phase of brown rot has been observed in Texas and it is of minor importance. Brown rot may become more prevalent as mayhaws are commercialized.
Cedar-Quince Rust (fungus – Gymnosporangium clavipes): Cedar- Quince Rust is the most destructive disease on mayhaw. Infection takes place in spring. Fungal spores for infection on mayhaw come from orange jelly-like growths on cedar limbs – Eastern red cedar primarily (See Photo). These spores are windblown from up to a mile away, indicating the alternate host for cedar-quince rust does not have to be in close proximity. Mayhaw fruit is more susceptible than young twigs. Leaves are seldom infected. After colonizing fruit the fungus erupts through the epidermis forming tubular orange structures full of spores (See Photo) that can only infect cedar or some similar alternate host. Infectious cankers on cedar are perennial. Therefore, yearly re-infection of cedar is not necessary to keep the disease active. Heavily infected mayhaw fruit does not ripen properly and is of no value. Fungicide protection up to four weeks after bloom or until fungal eruptions on cedar cease is essential for control. Fungicides are being developed but are not currently available.
Fire Blight (bacterium – Erwinia amylovora): The bacterium is spread by wind, rain and insects during bloom. Infected blooms die. Invading bacteria progress into tender shoots causing a shoot blight. The bacterium becomes inactive in hot weather. This is a spring and early summer disease that is generally not encountered every year. (See Photo)