Delayed dormant fungicide sprays are useful tools for controlling or reducing the inoculum for many diseases that attack small fruits. These fungicides work by suppressing overwintering fungal colonies and spores on twigs and bud scales. This suppression reduces primary inoculum in the spring, which eliminates or minimizes initial fungal infections on leaves and green shoots. This in turn reduces later season infections. The fungicides are intended to be used while plants are dormant or have just broken dormancy (delayed dormant). If more than Â½ inch of green tissue is present, these sprays may cause foliar burning and can damage floral parts.
Common delayed dormant fungicides include liquid lime sulfur (LS), Sulforix (S), and various forms of copper hydroxide (CH). Fungicide labels list the following small fruit diseases:
Blueberry: phomopsis cane and twig blight (LS, S); some activity against mummy berry (LS, S).
Blackberry: anthracnose (LS, S, CH), cane blight (LS, S, CH); some activity against Septoria leaf spot (CH).
Raspberry: anthracnose (LS, S, CH), cane blight (LS, S, CH), spur blight (LS, S, CH); some activity against yellow rust (LS, S, CH) and powdery mildew (LS, S).
Grape: anthracnose (LS, S), powdery mildew (S, CH); some activity against phomopsis cane and leaf spot (LS, S, CH), black rot (CH), and downy mildew (CH).
Delayed dormant fungicides are much more effective when accompanied by good sanitation. Remove and destroy primary inoculum sources such as mummified fruit, dead wood, and canes with cankers when pruning. Always read the fungicide label, follow all usage directions, and wear appropriate protective equipment when applying these fungicides. Note that several of these fungicides carry the signal word “DANGER”. As these sprays may have an unpleasant odor and can damage skin and eyes, try to complete pruning in advance of the fungicide application to reduce exposure. Do not apply liquid lime sulfur within 14 days of an oil spray, or when the temperature is above 75° F. Additional information on usage of delayed dormant fungicides is found in the Midwest Small Fruit and Grape Spray Guide, available from MU Extension offices and at https://ag.purdue.edu/hla/Hort/Documents/ID-169.pdf.
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REVISED: November 23, 2015