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Witches'
broom
Pucciniastrum goeppertianum
(fungus)
Annemiek Schilder,
MSU Plant Pathology
Bill
Cline, NCSU Plant
Pathology |
| Witches' broom is a relatively minor disease of
highbush blueberries, but it can be severe near balsam fir trees
(Abies), the alternate host for the rust fungus. |
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Symptoms
Diseased plants have broomlike masses of swollen,
spongy shoots with short inter-nodes and small leaves. Young
stems on the brooms are initially yellow or reddish, but later
become brown and shiny, and, eventually, dry and cracked.
Heavily infected plants produce no fruit. The brooms can
persist for many years, producing infected new growth every
year.
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| Swollen shoot of witches’ broom. |
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Disease cycle
Airborne spores produced on fir needles infect
blueberry leaves and stems in the summer. The fungus becomes
locally systemic and perennial in blueberries. Overwintering
spores develop in the swollen stems and, in the spring, produce
spores that reinfect fir needles. |
| Infected (left) and healthy (right) blueberry stems. |
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Management
Because the pathogen is systemic in the blueberry crown, pruning
will not eliminate the disease. Remove fir trees within 500 yards
(460 m) of planting; eradicate infected plants with a herbicide;
Rancocas is a resistant cultivar. |
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