Controlling powdery mildew requires using a few different fungicides. The way to ensure the highest ROI from your fungicide investment is to use them in the best order. Focusing on their core chemical attributes can help you determine when to use which one.
The three most commonly used groups of grape fungicides are sterol inhibitors (known as SIs and also DMIs), strobilurins and inorganics. Other classes of chemistries include quinolines (quinoxyfen) and ethylenebisdithiocarbamate or EBDC(Mancozeb). Rotating among them during the growing season brings the benefits of each chemical group together, delivering effective disease control while managing resistance development.
Researchers, including Doug Gubler of UC-Davis and Larry Bettiga of Monterey County Cooperative Extension, trust starting with a sterol inhibitor.
Sterol inhibitors, such as Viticure®, work by inhibiting the development of cell walls in the target organism. Without cell walls, the organism cannot survive. This type of chemistry is especially active against powdery mildew and can be applied in rotation throughout the season. Some SIs also control additional diseases. For example, in addition to powdery mildew control, Viticure suppresses black rot and Botrytis bunch rot.
Strobilurins, including pyraclostrobin and trifloxystrobin,interfere with energy production and cell respiration to prevent spore germination in fungi and inhibit mitochondrial electron transport.Applying strobilurins later in the season during bunch development not only supports a powdery mildew control program, but also helps prevent Botrytis bunch rot and grey mold.
Inorganic compounds, such as copper and sulfur, prevent fungi from attaching to plant surfaces. Fungi do not develop resistance to this type of material, making inorganic compounds an effective preventative tool, as well as a key component of resistance management in the vineyard. Most spray programs start with an application of sulfur at bud break and intersperse additional applications between strobilurin and sterol inhibitor applications during the growing season.
If you have questions about the best spray program for your acres, contact your PCA or your local Chemtura AgroSolutions representative.