Twig Blight of Blueberry
Fruit Disease Information Note 10
W.O. Cline, Extension Plant Pathologist
North Carolina Cooperative Extension Service
North Carolina State University
[Fruit Rot Stage] [Cane Canker Stage]
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is a fungal disease which causes a dieback
of fruit-bearing twigs on highbush and rabbiteye blueberry bushes. Yield
losses as high as 70% have been recorded on susceptible varieties when
fungicidal sprays are not used.
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.
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.
(Phomopsis vaccinii) overwinters in dead twigs infected during
the previous year. Beginning in February, spores (conidia)
are released from the old infections and dispersed by wind and rain. The
largest numbers of conidia are released from budbreak in February through
bloom in April; conidia become trapped in opening buds, germinate, and
infect the vascular system.
After the twig is killed, fruiting bodies called pycnidia
are produced just under the surface of the bark. these fruiting bodies
exude conidia which can cause additional infections, with conidial production
continuing into August.
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 July after harvest (topping) 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 Harrison are highly susceptible to this disease and should not be grown without using a fungicidal spray program. Croatan is moderately susceptible, while Reveille, Cape Fear, Bluechip and Wolcott are relatively resistant. Some rabbiteye cultivars are susceptible, especially Delite.
Chemical control can be obtained by spraying benomyl (Benlate)
50% wettable powder at a rate of 1 lb/100 gallons (2 tsp/gal). This fungicide
should be applied from budbreak through bloom on a 7-14 day interval;
benomyl cannot be applied within 21 days of harvest, so spraying should
be stopped soon after green fruit begins to size. Currently, the Benlate
label requires the use of a non-benzimidazole fungicide in combination
with benomyl to reduce the possibility of fungi developing resistance
to benomyl. Captan is the least expensive labeled fungicide for combining
with Benlate. For the most current information on chemical control, see
the North Carolina
Agricultural Chemicals Manual.
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.
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.
For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service personnel.
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Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data.
Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact your county North Carolina Cooperative Extension Service agent.
by the North Carolina Cooperative Extension Service
Web page last updated on October 2000 by A. V. Lemay.