April Walnut Orchard Management Considerations

Katherine Jarvis-Shean, UCCE Orchard Advisor, Sacramento, Solano and Yolo Counties Luke Milliron, UCCE Orchard Advisor, Butte, Glenn, & Tehama Counties
Janine Hasey, UCCE Farm Advisor Emerita, Sutter, Yuba, Colusa Counties

Please note that the following are general recommendations intended to help you keep track of regular practices in a busy time; the optimal timing for management practices may vary based on specific location and conditions.

  • Pistillate Flower Abscission (PFA): For varieties susceptible to PFA (especially Tulare or Serr), apply first ReTain® spray at 30 to 40% pistillate (female) flower bloom. The percent PFA and rate of bloom determines if a second spray is needed. ReTain® cannot be applied within 2 days of a copper application. PFA often occurs in years when trees have a heavy catkin load and pollen shedding overlaps with pistillate bloom.
  • Navel Orangeworm (NOW): Consider putting out navel orangeworm pheromone traps for adult males and traps baited with ground pistachio meal for adult females.
  • Scale: Monitor for scale crawlers by putting out double-sided sticky tape by early- to mid-April if scale has been a problem and you didn’t treat for scale during the dormant season.
  • Walnut Blight: Timing of your first walnut blight spray should depend on the orchard’s disease history and forecast weather. If rain is forecast and the orchard has high blight history, consider spraying as early as bud break or catkin emergence and then following up with a second spray 7-10 days later. If pressure in the block is moderate/low (low disease history or no rain forecasted), consider the timing of 20% prayer stage. Learn more here.
  • Bot Canker: Limbs that have been killed by Bot canker are easy to identify between budbreak and full leaf expansion but wait to prune dead wood until rain is no longer in the forecast.


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