Nectria twig blight, caused by the fungus Nectria galligena, is a minor disease that breaks out occasionally in Pennsylvania. This disease is a problem, however, in areas of coastal California where temperatures are more moderate. Because its symptoms are similar to those of fire blight, growers need to be able to recognize it. The chemical controls used for fire blight would not be used on nectria twig blight.

Symptoms

In early summer leaves and shoots of infected twigs wilt and turn brown. Close examination will show that a canker has girdled the twig at the point where shoots begin to grow. Most often this spot is located at the base of the previous season's cluster bud.

These young cankers are usually first observed at nodes and appear as elliptical, sunken areas. The fungus grows deep into the wood and will kill new wood callus as it develops. As a result of this annual killing of successive layers of callus, perennial, target-like zonate cankers form. As the cankers enlarge they girdle branches and twigs killing the shoot tissue. Canker margins are irregular and have a rough appearance due to the cracks in the bark. During humid weather, fruiting bodies of the fungus can be observed on the canker and appear bright red to orange on the surface.

Disease Cycle

The fungus survives in twig and branch cankers. Cool, moist weather favors the production of fungal spores.

Disease Management

Nectria canker is occasionally found on apple nursery stock shipped into the eastern United States from the western United States. Careful inspection of this stock material for symptoms of the disease should be done. Trees with canker should be discarded or returned to the nursery.

Cankers in the orchard need to be removed. Certain apple cultivars are more susceptible to nectria twig blight than others. Check with your local nursery supplier for specific cultivar recommendations.