We saw reports of bud burst and 1- to 3-inch shoots this past week in Wisconsin. Critical fungicide application timing is now for several grape diseases – Phomopsis, Black Rot, Powdery Mildew, and Downy Mildew. Control of these diseases early in the season can help prevent outbreaks later in the season. Remember to consult the NEWA predictions for grape diseases in your area.

We observed Phomopsis fungal fruiting bodies on several canes at the West Madison Ag. Research Station. Thank you to Emma Nelson for assistance with disease scouting.

Some areas may experience rain next week so keep a close eye on the forecast and be prepared to protect young, succulent grape tissues. Remember that early season management extends 3 to 4 weeks after bloom, so long-lasting protection is critical during this period, especially in vineyards with a history of disease and/or when conditions are conducive to infections.

Phomopsis cane and leaf spot infections are favored by cool and wet weather. Phomopsis can infect the fruit, and while symptoms on the fruit may not appear until later in the season, these infections happen pre-bloom to bloom. These latent infections of green fruit remain dormant until berries start to ripen. Inoculum of Phomopsis is expended early in the season, so the most critical time to protect from infection is pre-bloom. Phomopsis can also colonize dead wood, and if dead canes or cordons are left in the orchard they can serve as a source of inoculum. Removal of dead wood will help reduce disease pressure.

• Conventional Management: mancozeb, captan, and ziram are very effective at controlling Phomopsis during this early season period. Additional fungicides and their efficacy can be found in the 2021-2022 Midwest Fruit Pest Management Guide.
• Organic Management: copper and sulfur are not very effective against Phomopsis; they can also cause injury on some varieties. Removal of infected wood in the canopy is recommended.

Black rot infections are favored by humid conditions. Black rot infections can occur on the leaves and the fruit, and often initiate from spores on mummified fruits left in the vineyard from the previous year’s infection. Fortunately, a few weeks after bloom most varieties have ontogenic resistance (or age-related resistance) to black rot infections. With this in mind, sprays must be applied during the most susceptible period from pre-bloom through bloom.

• Conventional Management: mancozeb and ziram provide excellent control for early season black rot management. Additional fungicides and their efficacy can be found in the 2021-2022 Midwest Fruit Pest Management Guide.
• Organic Management: Several copper products are available for black rot control; efficacy is low to moderate depending on application frequency.

Powdery mildew infections are favored by humidity and shade. Fungal fruiting structures overwinter on the vine and release spores in the spring contributing to primary infections early in the season. Infections can continue as diseased tissues produce more spores throughout the season leading to epidemics. Controlling these primary infections will significantly reduce infections later in the season.

• Conventional Management*: Endura, Luna Sensation, Rally, Pristine, and several others listed in the 2021-2022 Midwest Fruit Pest Management Guide provide good to excellent control.
• Organic Management: sulfur* (must be reapplied frequently if dealing with wet weather); stylet oil can be applied pre-bloom to provide good powdery mildew control, but it can cause leaf injury on some varieties.

*Sulfur may not be applied within 10 days of an oil application

Downy mildew infections are favored by rainfall and high humidity. The pathogen overwinters as dormant spores in leaf tissue on the vineyard floor or within the upper soil layer. In the spring, during rainy periods, spores are produced and splashed onto susceptible tissue. After these primary infections begin, infection cycles can continue throughout the vineyard as new spores are produced on diseased tissues.

• Conventional Management*: mancozeb and captan provide good control of downy mildew; Revus and Revus Top provide excellent control. See additional control products listed in the 2021-2022 Midwest Fruit Pest Management Guide.
• Organic Management: Several copper products are available for downy mildew control; they are effective but require frequent application; some copper products may cause injury to the foliage.

*Powdery mildew and downy mildew are very prone to fungicide resistance. Rotate chemistries and avoid sequential applications of systemic fungicides from the same FRAC group.

Anthracnose infections are favored in wet years on susceptible varieties. Fungal inoculum overwinters on infected canes and when rain occurs in the spring, it splashes spores to young, susceptible tissues. This disease is most observed in wet, humid years, especially when these conditions occur around the bloom period.

• Management: Liquid lime sulfur dormant sprays are effective for limiting the production of spores; diseased canes should also be removed during the dormant season.

Mention of a fungicide is not an endorsement. The label is the law, consult the label directions before using any fungicide product.

This article was posted in Disease, Grapes and tagged Black Rot, disease, disease management, Downy mildew, Fungicides, Grapes, Leslie Holland, Phomopsis, Powdery mildew.