March Walnut Orchard Management Considerations

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

It is finally looking a like spring outside, and there are some tasks the walnut growers can do to stay on top of things. Below are some orchard tasks to keep in mind for walnut growers. 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.

  • Irrigation: Perform irrigation system maintenance now, before irrigation is necessary and system problems could cause tree stress. Check for broken or clogged filters and emitters. More information available here.
    • If you farm in Tehama, Butte, Colusa, Glenn, Shasta or Yolo counties, you can apply for a free system evaluation from the Tehama Resource Conservation District Mobile Irrigation Lab by contacting Kevin Greer (530) 727 – 1297, kevin AT tehamacountyrcd.org.
  • Weeds: Rotating and/or mixing herbicides with different modes of action (MOAs) is critical to good weed management, particularly of herbicide-resistant populations. But MOAs and labeled crops are not always easy to keep track of. Brad Hanson, UCCE Weed Specialist, has organized a chart to help, with herbicide name, a common trade name, the site of action group and the crops for which an herbicide has been labeled for use. This chart is a helpful tool, but remember that labels change often. Always check the herbicide label before use.
  • 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.
  • Codling Moth: Hang codling moth traps by mid-March to establish the first flight biofix (typically between mid-March and mid- April), begin tracking degree days, and evaluate pest pressure. Many effective mating disruptants are available (aerosols, hand-applied, flowables) and are becoming more affordable due to improvements in formulations, release rates, and release intervals. If using mating disruption, hang or apply disruptants ahead of historical biofix in your orchard. For more details on monitoring and managing codling moth, visit this site.
  • Navel Orangeworm (NOW): Consider putting out navel orangeworm pheromone traps for adult males and traps baited with ground pistachio meal for adult females.
  • 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.
  • Fungicides: Have your air-blast sprayer ready to apply bloom fungicides. Check calibration and do general maintenance (check sprayer filters, replace nozzles as needed, etc. Reference the fungicide timing and efficacy document as you plan your fungicide programs for the year. Remember to rotate FRAC groups for resistance management.
  • 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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