California Walnuts: 10 Orchard Management Tips For April

#1. Evaluate orchard for blight spray.

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. Here’s more details on predicting walnut blight risk, choosing materials, and avoiding common management pitfalls.

#2. Look for dead limbs.

Limbs that have been killed by bot canker are easy to identify between budbreak and full leaf expansion, but wait to prune deadwood until rain is no longer forecast. If timing Bot treatment based on the Leaf Wetness Model, watch for storms that bring ¼ inch or more rain and temperatures of at least 50 degrees.

The Leaf Wetness Model can be found here. New research is finding that controlling hull infections by Botryosphaeria (Bot), Phomopsis, Aspergillus, Alternaria, and Fusarium also helps reduce kernel mold.

#3. Calibrate, calibrate, calibrate.

Good spray coverage is critical to management of walnut blight. One of the prerequisites for good spray coverage is a calibrated sprayer.

#4. Don’t let codling moths sneak up on you.

Codling moth traps should have been put out by mid-March to establish the first flight biofix (typically between mid-March and mid- April), begin tracking degree days, and evaluate pest pressure. Temperatures in February and early March 2020 are pointing to potentially earlier first biofixes this season.

If temperatures stay relatively moderate to warm throughout March and April, keep a close eye out for earlier biofixes and generation timings throughout the remainder of the season.

Ideal degree day model treatment timings maybe skew to the much earlier side than “normal” this year. Here are details on monitoring and managing codling moth.

#5. Monitor for NOW…perhaps.

Consider putting out navel orangeworm (NOW) pheromone traps for adult males and traps baited with ground pistachio meal for adult females.

#6. Begin checking for scale crawlers.

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.

#7. Consider applying ReTain.

For varieties susceptible to pistillate flower abscission (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 when trees have a heavy catkin load and pollen shedding overlaps with pistillate bloom.

#8. Line up foliar zinc, if needed.

Apply foliar zinc if needed, based on leaf sample analysis or symptoms. Apply when shoots are 6 to 10 inches long, when zinc can be easily absorbed through the leaf surface. If the deficiency is severe, additional sprays can be applied two more times every 2 to 3 weeks.

#9. Check over irrigation systems.

Perform irrigation system maintenance now, before irrigation is necessary and system problems could cause tree stress. Check for broken or clogged filters and emitters. Here are more tips on maintaining micro-irrigation systems.

#10. Determine if you really need to irrigate quite yet.

Before you start irrigating, consider plant water stress (pressure chamber) measurements and soil moisture sensor readings. Recent research in the Sacramento Valley has found irrigation can be delayed until June in some years, saving water and pumping costs without negative impacts to yield, size or quality.

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