Agriculture Reference
In-Depth Information
Fabraea Leaf Spot and Pear Leaf Spot
Fabraea leaf spot is caused by the fungus
Entomosporium maculatum
(
Fab-
raea maculata
) that infects apple leaves and the leaves, fruit, and shoots
of pear and quince. A similar but less serious disease, pear leaf spot
(Mycosphaerella leaf spot or
Mycosphaerella pyri
), infects pears, quince, and
sometimes apples. Most European pears are susceptible to Fabraea leaf spot.
These diseases are not much of a problem in arid and semiarid regions but
can be very serious under humid and rainy conditions. Fabraea leaf spot is
widespread in eastern North America.
Symptoms.
Fabraea leaf spot symptoms begin as small purple dots on the
lowest leaves. These dots gradually enlarge to form brown to black spots
that are
⁄
8
to
⁄
4
inch in diameter with purplish-black centers. Raised, blister-
1
1
like fruiting bodies (acervuli) in the centers of the spots ooze a mucous-like
material when wet, appearing as creamy or glistening areas on the leaves.
In severe infections, defoliation can occur quickly and is common in humid
areas. Fruits on infected trees develop similar spots and are usually small,
misshapen, and cracked. Fewer fruit buds form, decreasing the following
year's crop. Fall blooming may also occur. Superficial cankers form on the
twigs but usually disappear by the following year. Trees can become stunted.
The pathogen overwinters mostly on fallen leaves and can also over-
winter in twig lesions. New infections may not develop until late spring or
early summer, and secondary infections begin developing about 1 month
later during wet weather. Wind spreads late-summer spores. Infection can
occur during wet periods lasting no more than 8 to 12 hours, so it is import-
ant to apply protective sprays before infections occur. Monitor the lowest 20
leaves on a test tree. From 1 to 10 spots indicate a moderate risk of serious
damage. More than 10 spots, total, on the 20 leaves indicate a high risk.
Management.
The same strategies are used to control Fabraea leaf spot and
pear leaf spot. Remove or shred fallen leaves to reduce spore formation, as
