As growers make this season’s fungicide sprays, helpful diagnostic tables are available online at the UC ANR website to help decide what the best fungicide is for an orchard at a given time. The tables were created by UC Riverside’s Jim Adaskaveg, Extension Plant Pathologist Emeritus Doug Gubler and Plant Pathologist Themis Michailides.
“The tables show the efficacy of a wide range of fungicides against specific pathogens, which will allow folks to pick the best product for the task at hand,” said UCCE orchard crops farm advisor Phoebe Gordon.
The tables currently offer fungicide efficacy and timing recommendations for almond, pistachio and walnut as well as major tree fruit crops. In Figure 1, a table showing almond fungicide efficacy can be seen, which provides a list of fungicides that have been tested along with their efficacy against common diseases. The symbols on the table (++++, +/-, —-, etc.) represent a rating for how effective a fungicide is in treating a specific disease. The efficacy table also contains a resistance risk number assigned to each fungicide by the Fungicide Resistance Action Committee according to different modes of action.
It should be noted that the provided efficacy tables are not consistently updated for a specific crop or disease, nor do they contain all registered fungicides for a given crop. Ultimately, fungicide labels should be followed to ensure proper and lawful use.
The other set of tables (Fig. 2) provided show a list of effective spray timings for diseases of a given crop. The tables provide multiple effective windows for treating a disease in case a grower wants to start treating earlier or later in a season. It should be noted that, while there is more than one effective time of the season to spray for a disease, sprays don’t need to be made during every effective window.
Proper timing of fungicide sprays is crucial to successful disease prevention and control in an orchard. Fungicides are a protectant against disease and need to be applied in advance of an infection event, according to Gordon.
“If you want your spray to be effective and not waste money, you want to make sure you are spraying when research has shown that a spray will do what it’s supposed to,” Gordon said.
This is assuming that a grower needs a spray for a given orchard based on scouting, she said, such as looking for shothole fruiting structures in the fall, for example.