Diplocarpon mespili
Overview
- Fabraea leaf spot is a fungus (Diplocarpon mespili) that infects primarily leaves and fruit of pear and quince. Infections can result in significant leaf spotting, defoliation, and unmarketable fruit.
- Fabraea leaf spot infection occurs from spring to summer, and like apple scab, spores are released and spread during periods of rainfall.
- Sanitation by flail mowing leaves and brush may help reduce Fabraea leaf spot spores, however, chemical control is still usually necessary.
- Chemical control using contact fungicides beginning in the spring and continuing into the summer in wet years are necessary to control Fabraea leaf spot.
Symptoms & Signs
Fabraea most noticeably first manifests itself as small, purple-black spots on leaves and fruit. Spots gradually enlarge into brown lesions 1/8 to ¼ inch in diameter. When the infection is severe, defoliation can occur and fruit will become deformed and not sellable and/or drop off the tree. Fabraea may also infect shoots, again appearing initially as purplish spots, becoming lesions/cankers which may persist into the next growing season. Leaf and fruit infections are most notable in the Northeast and Midwest, but in the Southeast , shoot infection can be significant. Severe infections can result in reduced flower bud formation for the following season.
Disease Cycle
Similar to apple scab, much Fabraea overwinters in leaves on the orchard floor. Farther south, overwintering is also likely to occur in shoot cankers. Spores are released from leaves with rain from mid-May to July (in the Northeast and Midwest) and result in primary infection on fruit and foliage. Shoot cankers spread Fabraea from late-April through May (in the Southeast) with more driving rains. Length of wetting for infection to occur can range from 12 hours at 50 degrees F. to as little as 8 hours from 68 to 77 degrees F. Infections take about 7 days to become visible. Once primary infection occurs, secondary infection can spread rapidly with rain and wind during the summer, particularly during wet seasons.
Chemical Control
Contact/protectant fungicides are necessary to control Fabraea leaf spot. EBDC fungicides (Manzate, Penncozeb, Dithane) and Ziram give good control. (But EBDC’s have a 77 day Pre-Harvest Interval.) Early season fungicide application(s) for pear scab (as long as EBDC’s or Ziram are included) will prevent initial infection by Fabraea. Where disease pressure is high, however, summer-long fungicide applications (once the pear scab season has passed) will be required, particularly in wet summers. Late-maturing varieties may even need fungicide sprays into the early fall to prevent Fabraea from infecting fruit.
Fungicide Resistance in the Eastern U.S.
None known because contact fungicides are necessary for control.
Non-Chemical Control
Biological Control
Other than sanitation, there is no known biological control of Fabraea leaf spot.
Cultural Control
Flail mowing/chopping leaves and brush and removing obvious cankers on the tree may help to control Fabraea leaf spot and is recommended.
Resistant Varieties
Although there are some variety differences in susceptibility to Fabraea leaf spot, generally just consider the fact all European pear varieties are susceptible such that the disease will need to be controlled. Bosc and Seckel, however, appear to be especially susceptible to Fabraea.
Links
http://www.scaffolds.entomology.cornell.edu/1999/6.7_diseases.html
