I. Introduction: Brooks spot is a minor disease that occurs throughout the northeastern and mid-Atlantic
apple growing regions of the U.S. and occasionally as far westward as Iowa. Some of the
more susceptible common commercial cultivars include 'Jonathan', 'Golden Delicious',
'Stayman Winesap', 'Grimes Golden', and 'Rome Beauty'.
II. Symptoms: Brooks spot first appears as
irregular, slightly sunken dark green lesions typically on the calyx end of immature apple
fruit (photo 2-37). As the fruit matures, the lesion turns dark red or purple on red areas
of the fruit and remains dark green on green or yellow areas (photo 2-38). The disease is
sometimes confused with the physiological disorders Jonathan spot, cork spot, and bitter
pit. However, Brooks spot usually appears earlier in the season and shows little browning
of the flesh underneath the lesion. Jonathan spot lesions are usually more round and the
lesion edge is more abruptly sunken, with a shallow browning of the flesh underneath.
III. Disease Cycle: Primary
infection is initiated by ascospores which are discharged from
overwintering leaves in late spring and early summer.
Ascospores germinate in six hours at 61 to 75 F (16 to 24 C). Leaf
infection through stomata can occur after 96 hours of continuous wetting
at 68 F (20 C), but infection may be enhanced by alternating wetting and
drying conditions. Fruit lesions appear in July and August. Secondary
infection is not known to occur. Leaf infections remain inactive until
late summer when small purple lesions begin to appear. Following leaf
fall, the fungus colonizes the leaf extensively.
IV. Monitoring: Ascospores
are discharged from overwintering leaves in late spring and early summer. Wetting periods
of six hours or more at 61 to 75 F (16-24 C) can be recorded as infection periods. Fruit
lesions may begin to appear in early July. Monitoring of fruit symptom development (photo
2-37) is useful to improve recognition of this minor disease and its control in subsequent
years; however, by the time symptoms are recognized it is usually too late to control in
the year of infection and there is no secondary infection.
V. Management: Most of the fungicides used
in the early cover sprays for summer diseases are effective against the Brooks spot
fungus. The sterol demethylation inhibitor (DMI) fungicides used for early season
scab, mildew, and rust control are ineffective.
Text prepared by K. S. Yoder
Download this file in pdf format (Acrobat Reader required).