Blueberry rust has been reported in rabbiteye blueberry cultivars in Alabama. Leaf rust, caused by the rust fungus, Pucciniastrum vaccinii (synonyms: P. myrtillus, Naohidemyces vaccinii, and Thekopsora vaccinii), has the potential to be very damaging to yields, and is most prevalent in the southeastern United States. Rabbiteye cultivars suffer from premature defoliation, while highbush blueberries are subject to occasional localized outbreaks.
Symptoms of Blueberry Rust
The first symptoms appear as yellow leaf spots on the upper leaf surface of newly emerged blueberry leaves (Figure 1). As the disease progresses, spots turn reddish brown (Figure 2). Entire leaves may turn brown, die and drop prematurely if infections are severe. Yellowish orange pustules become visible on the lower leaf surface about mid-summer. Blueberry rust can lead to a loss in yield and a reduction in flower buds next year due to defoliation in susceptible varieties.
Airborne spores infect newly expanded blueberry leaves in the spring. Leaf spots usually become visible in mid-season. Spores released from rust pustules formed in mid-season on blueberry lower leaf surface below these leaf spots my re-infect blueberry leaves, leading to disease build-up on blueberry bushes. Telia (a structure of the reproductive rust disease cycle) form in the blueberry leaf late in the season. They appear as flat, dark-colored crusts on the lower leaf surface. Leaves infected with telia drop to the ground where the fungus overwinters. Pustules can be seen on newly infected leaves 10 days after inoculation. The fungus’s alternate host hemlock needs to be present for the disease cycle to be completed. Leaf rust is most prevalent in areas within the natural range of hemlocks.
Implementing a preventive control program to control rust includes:
- removing hemlock trees within a third of a mile
- avoiding susceptible cultivars
- limiting overhead irrigation
- and applying effective fungicides.
Even with frequent fungicide sprays, however, this disease may prove too difficult to manage. Fungicide sprays may also cause phytotoxicity to blueberry leaves, so they must first be tested and tank mixes of incompatible products must be avoided. For current fungicide recommendations, consult your local extension agent or see the Southeast Regional Blueberry Integrated Management Guide.
One of the best ways to control blueberry leaf rust is to plant a resistant variety. A Cornell University online report lists Northern highbush varieties resistant to blueberry rust to include: Bluecrop, Burlington, Collins, Dixie, Earliblue, Gem, Ivanhoe, Olympia, Stanley, and Weymouth. Moderately susceptible varieties are: Jersey, Herbert, Berkeley, Blueray, and Pacific. Susceptible varieties to blueberry rust include: Coville, Pemberton, Washington, and Atlantic.