Katherine Jarvis-Shean, UCCE Orchard Advisor, Sacramento, Solano and Yolo Counties Luke Milliron, UCCE Orchard Advisor, Butte, Glenn, & Tehama Counties
Jaime Ott, UCCE Orchard Advisor, Tehama, Shasta, Glenn, and Butte Counties
Clarissa Reyes, UCCE Orchard Advisor, Sutter, Yuba, Butte, and Placer 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.
• Nutrition (Zinc): If last year’s leaf analysis indicated zinc deficiency, apply foliar zinc when shoots are 6-10 inches long, when zinc can easily be absorbed by the leaf surface. This will ensure the maximum benefit from your investment. Blends with additional micronutrients will likely not show a return for the additional cost. Zinc is critical for carbohydrate production that leads to nut fill and stress responses that can avoid other quality issues. It’s worthwhile to correct a deficiency, but for orchards that are not deficient, a spray is probably not worth the investment this year.
• Weather: Keep an eye on the weather to prepare for a potential spring freeze. If a freeze is in the forecast, ensure that your orchard soil is moist, and that any groundcover is mowed to below 2”. This allows sunlight to heat the orchard floor during the day, warming the orchard at night. Running sprinklers during the frost can also provide some protection.
• Irrigation prep: If you’re going to invest in applying water and nutrients this year, make sure it will get where it is needed through irrigation system maintenance. Check your irrigation system and address maintenance issues now, before they cause tree stress and reduced yields, and before expensive nutrients get concentrated in some zones and shorted in others. Check for broken or clogged emitters, splice new line into sections with temporary repairs from last season, and replace/refill filter media if needed. Contact your county’s Resource Conservation District Mobile Irrigation Lab for a free assessment of your irrigation system before the irrigation season begins.