Grapevines are in early stages of growth across the state, from bud break to 10 inch shoots. Significant shoot growth is expected with the warm weather predicted for this week. This is a very important time to maintain preventative control over major grape diseases including Phomopsis, black rot, powdery mildew and downy mildew. Fungicide application should begin at 1-3 in shoot growth and should be repeated at 7-10 day intervals according to label instructions and environmental conditions through bloom, especially prior to a predicted rain event. See Table 1 for Foundation Fungicide Program for Early Season Control of Grapevine Diseases.
Please note that downy and powdery pathogens are especially prone to fungicide resistance. To avoid this, do not apply back-to-back applications of any one systemic fungicide class.
Table 1. Foundation Fungicide Program for Early Season Control of Grapevine Diseases.
For further information, see the Midwest Fruit Pest Management Guide.