Protect new grape shoots from early-season fungal diseases
Cover spring grapevine growth with fungicides or other protectants this rainy spring.
The buds on grapevines in the southern part of Michigan have opened, and shoot growth has begun in earnest. In Van Buren and Berrien counties, shoots are a few inches long on Concord and Niagara grapes, and buds have now broken in wine grapes. With recent and upcoming rains, these new shoots are vulnerable to infection from phomopsis (Phomopsis viticola) and, in some varieties, anthracnose (Elsinoe ampelina). Both fungi can cause damage to leaves, shoots and fruits. New growth and exposed flower clusters are most vulnerable to infection.
Any phomopsis or anthracnose that survived the winter in the vineyard will release spores during spring rains. Spore release begins at bud break and continues until grape bloom, possibly longer. Young shoots infected by Phomopsis develop lesions as the year goes on, which will produce spores in turn next year. For this reason, Michigan State University Extension recommends that even grapevines not expected to crop this year due to winter damage should be protected in the early season.
Powdery mildew (Uncinula necator) may also infect new growth, especially in vulnerable varieties. In most cases, protection isn’t needed until fruit clusters become visible. That’s because the best weather for the fungus’ development often does not occur until June or later, even though spore release is happening now. Last year, MSU Extension observed more powdery mildew in the field than usual, including in the juice grape varieties Concord and Niagara. In any vineyards that experienced a serious powdery mildew outbreak in 2014, expect more of this disease in 2015.
Protectants like Manzate or Ziram (phomopsis, anthracnose), Sulfur (powdery mildew, anthracnose) and inexpensive systemics like Tebuzol (powdery mildew, anthracnose) and Phostrol (phomopsis) are most appropriate at this time of the season. Especially if growth was not covered during the previous wet period over the weekend, a systemic may give a little bit of back action for recent infection. It is better to save high-powered or expensive systemics (e.g., Pristine, Torino, Vivando, Inspire Super) until bloom or later stages of development to capture a broader spectrum of diseases and reduce costs.
Organic growers should achieve good efficacy on anthracnose and phomopsis with biocontrol agents like Serenade and Double Nickel. Consider adding NuFilm or similar spreader-sticker to biological products.