Cause Phacidiopycnis washingtonensis and Sphaeropsis pyriputrescens have become a problem in apple orchards with 'Manchurian' crabapple pollinizers that are very susceptible to these fungi and are a significant source of inoculum for apple storage rots. The disease in apples is called Speck rot and Sphaeropsis rot, respectively. Fruiting bodies on twigs and fruit contain millions of spores, which serve as inoculum for fruit or twig infection. These fungal spores are then spread by rain, irrigation water, or over-tree cooling. Madrone and persimmon are additional hosts.
Several other canker pathogens common to apple also occur on crabapple. OSU Plant Clinic records indicate that anthracnose (Cryptosporiopsis curvispora) and perennial canker (Cryptosporiopsis perennans) as well as the opportunistic fungi Cytospora, Cylindrocarpon, and Nectria cinnabarina as well as Phomopsis occur on crabapple samples. Cankers caused by the bacterium Pseudomonas have also been diagnosed several times.
Symptoms Twigs become discolored, dry, and dieback. Small branches may become girdled and turn light-brown distal to the leading edge of the canker. The cankers may transition from a light-brown dieback into a dark-brown area before transitioning into health wood. The dead, papery, light-brown epidermis may be seen flaking off these dead twigs. Larger limbs may also die. Many black dots (fruiting bodies) may be seen in the cankered tissue. Crabapple fruit may also be infected becoming dark, mummified, and developing many fruiting bodies.
- Remove and destroy cankers, dead twigs, and mummified fruit.
- Avoid overhead irrigation.
- Limit over-tree cooling to keep trees wet for shorter periods of time.
Use of these preharvest in apple orchards will aid in management of fruit rots.
- Pristine at 14.5 to 18.5 oz/A. The addition of a silicone-based surfactant has improved control. Can be used day of harvest. Group 7 + 11 fungicide. 12-hr reentry.
Use of these may also be effective in crabapple nurseries. Some other materials used for management of scab or powdery mildew may also be useful.
- Thiophanate-methyl-based products. Use in a tank-mix with other products. Group 1 fungicides. 12-hr reentry.
- Cleary's 3336 EG at 12 to 16 oz/100 gal water. Do not use after fruit set if applied to fruiting trees.
- OHP 6672 4.5 F at 10.75 to 20 fl oz/100 gal water. Do not use treated fruit for food.
- Systec 1998 FL at 20 fl oz/100 gal water. Washington Only.
- Tee-Off 4.5 F at 10.75 to 20 fl oz/100 gal water plus a surfactant.
Reference Xiao, C.L., Kim, Y.K., and Boal, R.J. 2009. A new canker disease of crabapple trees caused by Phacidiopycnis washingtonensis in Washington state. Plant Health Progress, doi:10.1094/PHP-2009-0612-01-BR.