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Soil Testing
and Plant Diagnostic Services
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Plant Diagnostic Clinic
573-882-3019
Cedar apple rust galls, above left, seen on juniper in the spring produce the spores that infect crabapple leaves.
Cedar apple rust lesions on foliage.
Numerous small, yellow spots appear on the upper leaf surfaces, usually during late April or May. Later, cluster cups are evident on the underside of the leaf spot. The fungus that causes this disease also produces galls on juniper.
Plant resistant varieties. Although eradicating junipers is not feasible, removing galls from nearby junipers may be of some benefit. Avoid planting crabapples adjacent to junipers.Fungicides can provide good control, with proper timing. Make the first application when gelatinous, orange tendrils are noticed on the cedar galls, usually in mid-April. Continue the applications on a 7 to 10 day interval as long as galls are active. Chlorothalonil (for crabapples not intended as food only), fenarimol, ferbam, mancozeb, maneb, myclobutanil, propiconazole, thiophanate-methyl or triadimefon are labeled.
General and serious. New shoots appear as if scorched by fire. Leaves cling to twigs and have "shepherd's crook" appearance. Plant resistant varieties. Prune in late winter or late summer or fall, not in spring. In dry weather, cut diseased branches and twigs 12 to 18 inches below visibly infected area. For commercial growers, spray streptomycin (100 ppm) in early or fall bloom to inhibit fire blight. Not recommended for home use.
Whitish powdery patches on young leaves, buds, blossoms and twigs. May cause growth irregularities. Does not usually require control. When serious, follow spray schedule under apple scab. Use chlorothalonil, fenarimol, mancozeb, myclobutanil, propiconizole, thiophanate-methyl, wettable sulfur or triadimefon. Resistant varieties available.
Serious in wet seasons. Dull, olive to black, velvety or scurfy spots on leaves. Leaves may turn yellow and fall off. May also appear on fruit.
Plant resistant varieties. Collect and remove fallen leaves. To prevent, follow a regular spray schedule, starting when first leaves appear until petal fall at six- to seven-day intervals, then 10- to 14-day intervals for remainder of season. Use chlorothalonil, fenarimol, ferbam, myclobutanil, propiconizole, thiophanate-methyl or sulfur.
Updated 10/9/07
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