Consideration should be given to your Phomopsis management program with budbreak approaching. Valley growers should consider applying a fungicide to protect young succulent growth prior to spring showers. Phomopsis viticola pycnidia will begin producing spores that infect susceptible cultivars such as Thompson Seedless, Flame Seedless, Redglobe, Grenache and others. Timely fungicide applications are paramount to good Phomopsis management.
Springtime management
Registered fungicides applied from budbreak through 12” of growth (mid March-May) act as foliar protectants and need to be applied prior to rain events to new growth after budbreak.
Copper/sulfur mixes work as foliar contact protectants when applied before rain events, with additional applications needed after heavy rains and new growth appears. Fungicides from this group should be considered for early season management due to canopy size and costs.
Strobilurin fungicides work as foliar systemics and sustain activity throughout long rain events. Unlike the contact protectants, they have the advantage of not being washed off during a rain event. Care should be taken to rotate the strobilurins with fungicides that are multiple site inhibitors (copper/sulfur). As the canopy continues to grow (4-6”), these fungicides should be considered as replacements for the non?systemic fungicides. Their efficacy during storms lasting more than a day will help protect new susceptible tissue.