W.O. Cline, Extension Plant Pathology
Visible symptoms first occur in late February to early March in southeastern North Carolina, soon after the flower buds reach the green-tip stage. Individual buds turn brown and die, followed by browning and necrosis of bark around the bud as the fungus spreads from the blighted bud into the twig. The disease usually spreads down the twig until most or all of the flower buds on an individual twig are killed.
Twig blight can continue to infect fruit-bearing twigs at all stages of development. New infections occur continually as buds open, flower, and produce fruit. The disease stops progressing after killing the twig (6-10 inches), and does not progress further down the stem to infect older wood. The slender leaf-bearing buds which develop lower on the twig are not initial points of infection with this disease, but they may be killed as the infection spreads down from the flower buds.
1. Pruning can be performed to remove infected twigs prior to spore release in the spring. This will decrease the amount of disease inoculum present at budbreak. While this technique may not be practical for large commercial operations, growers with less acreage and home gardeners should benefit from this sanitation method. Commercial growers who mow bushes in June and July after harvest (topping, hedging) will also benefit from the removal of blighted twigs that would otherwise overwinter and provide spores to infect new twigs.
2. Careful cultivar selection can greatly reduce the amount of twig blight experienced. The highbush cultivars Murphy and Bounty are highly susceptible to this disease and should not be grown without using a fungicidal spray program. Croatan, O'Neal and Legacy are moderately susceptible, while Reveille, Bluechip and Duke are relatively resistant. Some rabbiteye cultivars are susceptible, especially Delite.
3. Chemical control can be obtained by spraying fungicides from budbreak through bloom on a 7-14 day interval. For the most current information on chemical control, see the NC Ag Chem Manual.
Fruit Rot Stage
Phomopsis vaccinii also causes a fruit rot on blueberry at harvest in North Carolina. Infected berries become very soft and may split, resulting in leakage of juice. The cultivar Harrison is extremely susceptible and for this reason is no longer recommended for planting in NC. Most other varieties can be grown with minimal loss due to the fruit rot stage if fruit is harvested in a timely fashion to avoid overripe fruit on the bush. In North Carolina, fruiting bushes should be harvested every 7 days or less. Cane Canker Stage
In southern Michigan and northern Indiana, this fungus causes a cane canker which kills entire stems. Symptoms are similar to those of blueberry stem blight, a common disease in the southeastern United States. This disease stage of Phomopsis vaccinii has not been observed to occur in North Carolina.
South Region Small Fruit ConsortiumNC Ag Chemicals Manual Horticulture Information Leaflets (HIL) Home Page HIL-201 Suggestions for Establishing a Blueberry Planting in Western North Carolina HIL-201-B Principles of Pruning the Highbush Blueberry HIL-201-E Blueberry Freeze Damage and Protection MeasuresNorth Carolina Insect NotesNCCES Educational Resources