Coryneum Blight (Shothole)
- Ornamental and nut-bearing almond
- Stone fruit trees
Coryneum blight (Wilsonmyces carpophilus), also known as shothole blight, is a fungal disease that can cause damage on peach, nectarine, apricot, almonds (ornamental as well as nut bearing), and to a lesser degree, cherries (tart and sweet). Coryneum blight is caused by the fungal pathogen Wilsonmyces carpophilus. The pathogen can infect buds, twigs and branches, blossoms, leaves, and fruit. The disease is most damaging in extended cool and moist conditions of spring, although this disease can occur and cause damage at anytime during lengthy wet weather.
The fungal pathogen overwinters in infected buds and cankers on infected twigs and branches. Spores produced from these infected tissues, in the early spring, are dispersed during rain events to infect new buds. Later in the season, other susceptible tissues can become infected when there is suitable moisture on leaves and fruit. The spores, called conidia, are pigmented and are extremely durable. They can survive, exposed in a dormant state, on the surface of a bud for months, waiting for just the right temperature and moisture conditions to germinate and infect its host. This pathogen often surprises growers as it is active in the early spring at cold temperatures.
- Small round purple to tan lesions that are seldom 1/4 of an inch on leaves
- Raised circular to slightly elipsoid lesions on leaves
- Holes in leaves ("shothole")
- Darker buds
- Purple spots on fruit that become white to gray lesions
Cultural control practices involve removing infected twigs and branches by pruning and destroying wood. Thorough pruning during the dormant season is very effective and recommended for the homeowner as a major component of management to control this disease. In the spring at shuck fall, fungicides such as Abound, Pristine, Gem, Echo 720, Bravo Weather Stik, and Ziram, are effective. For commercial growers, protective fungicides should be used during frequent wet weather events.