Nectria twig blight of apple is caused by the fungus Nectria cinnabarina (asexual stage = Tubercularia vulgaris). This opportunistic, weakly pathogenic fungus invades winterkilled twigs, wounds, and fruit stems from the previous year’s harvest. The shallow cankers slowly expand and girdle infected stems. In June and early summer, the disease may exhibit symptoms similar to those of fire blight: new shoots wilt, the leaves brown, and a shepherd’s crook may form.
For proper diagnosis it is important to closely examine the affected shoot. In contrast to fire blight, the shoot and leaves typically die because of a canker below the affected tissues, often at the base of the previous season’s fruit cluster bud (rather than dying from the tip back); the canker margin is distinct; and there is no bacterial ooze. By midsummer numerous .5- to 3-mm orange/pink erumpent mounds, the asexual stage, form on the necrotic tissue. Nectria twig blight is most common on Rome Beauty but has been noted on Empire, Fuji, Northern Spy, and Granny Smith. |
