Answer: The only species you need to remove are eastern red cedars (Juniperus virginiana) and Rocky Mountain junipers (Juniperus scopulorum), says Herb Aldwinckle, a plant pathologist specializing in apples at the New York State Agricultural Experiment Station in GenevA. Eastern red cedars are native to east and central North America; Rocky Mountain junipers are found only as introduced cultivars at local nurseries. There must be a susceptible apple variety and juniper species within a few hundred feet of each other for this fungal disease to complete its tow year life cycle, Aldwinckle explains. Small brown galls form on cedars during the summer but do not mature until the following season, when they swell in warm, rainy spring weather and sprout orange spore producing horns. Spores blow to nearby apple trees, where they cause yellow rust spots on the leaves and young developing fruits. Spores then form on these spots in late summer and blow back to nearby cedar trees. The infected fruit is malformedand may drop prematurely. The best control is to plant resistant apple varieties such as MacIntosh, Red Delicious and Liberty. If you're growing some of the highly susceptible varieties like Golden Delicious, Rome Beauty and Jonathan, remove any redcedars or Rocky Mountain junipers within at least several hundred feet of your apples, says Aldwinckle. If this isn't practical, you can also control the disease by spraying the apples with maneb when the flower clusters open and again one week later, he adds.
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