That’s where the UC IPM weather network can pay off. It provides links to information or models for using the weather data to manage a wide range of crop pests and diseases. This can help you determine the current stage of development of the various disease and pest threats and when it makes economic sense to treat for them.

Weather information related specifically to grapes, including some readings taken within the grape canopy, is available from the nine weather stations in the Fresno-Madera Grape Network, five in San Joaquin County and a total of five within El Dorado, Calaveras, and Amador counties

For grapes, that includes powdery mildew, the omnivorous leafroller and the orange tortrix (a grape pest in the coastal areas and valleys where there is a marine influence for part of the day) which causes the same kind of damage as the omnivorous leafoller in inland areas).

In the case of powdery mildew, for example, the UC IPM Weather Network site provides a link to the UC IPM Pest Management Guidelines for this disease, including recommendations for monitoring and controlling it using information from a nearby weather station in the network or your own weather station to calculate the Risk Assessment Index. This index is useful for determining disease pressure and how often you need to spray to protect the vines.

“The powdery mildew risk assessment index isn’t a silver bullet that will eliminate problems with the disease,” Jordan says. “Its value is in helping you spend your pest control dollars wisely. For example, if the index shows a low risk of powdery mildew pressure, you may be able to reduce your number of sprays during the season and save some money. On the other hand, in a year like this one, when the index showed an extremely high risk of the disease for three straight months in some areas of the San Joaquin Valley, growers who timed their sprays accordingly can confirm they made a good investment in powdery mildew control.”

Jordan encourages growers to explore the UC IPM Weather network to learn more about the wealth of useful information it provides. “It offers a number of features you may not be aware of,” she says. “Once you become familiar with it, it’s a really cool tool.”