Nectria twig blight has recently been identified in a few commercial orchards in Ontario. This disease is easy to misdiagnose as the symptoms are very similar to those of fire blight. Symptoms begin to appear in late June, and result in the dieback of twigs and small, sunken cankers can be found at the base of the dying shoots. However there are a few features that distinguish nectria twig blight from fire blight. Nectria twig blight originates from the base of the twig where the canker has girdled the stem and progresses upwards, while fire blight originates from the tip of the shoot and progresses down the twigs. Another identifying feature of nectria twig blight is the presence of bright orange or pink spores that can sometimes be found on the cankers. The characteristic bacterial ooze found in fire blight infections is also absent in nectria twig blight.
Nectria twig blight is caused by an opportunistic fungus, Nectria cinnabarina, and can invade winterkilled twigs, last year’s fruit stems, and wounds. In contrast to fire blight, nectria twig blight is a minor disease of apple trees and rarely results in serious economic losses. When identifying disease in your orchard make sure to take a close look at the damage to determine if it is in fact fire blight or nectria twig blight. Correct disease identification is important because these two diseases have different control measures; since nectria twig blight is a minor disease there are no chemical control options, and fungicides aimed at fire blight will be wasted. The twigs infected with nectria twig blight should be removed in order to reduce the carryover of the inoculum and the spread of the disease to maintain tree health.