Effective dormant strategies for nut growers: Orchard sanitation, chill and irrigation management

Winter may seem quiet in the orchard, but what growers do during dormancy has a big impact on next season’s harvest.

National Nut Grower spoke with Mae Culumber, nut crops farm advisor with Cooperative Extension Fresno County, about essential tasks — like mummy hygiene, weed control, and pest scouting — that keep almonds, pistachios, pecans and walnuts healthy and ready for their next harvest.

How important is the dormancy period?

Mae Culumber (MC): This is an extremely important time to take note of the previous season’s lessons from leaf tissues analyses and grade sheet quality ratings. This can help you adjust nutrition, irrigation, and pest and disease management for the next growing season.

What advice would you provide growers of the major nuts on dormancy?

MC: Nut mummy sanitation, diseased canopy sanitation, weed control, irrigation system maintenance and pest scouting are worthwhile dormancy activities that will improve efficiency and improve nut quality when it comes time to harvest next season.

What should growers do during the winter to ensure adequate chill hours?

MC: Chill is needed to accumulate the carbohydrates the tree will need at bud break to bloom and leaf out uniformly. Growers should track chill portion accumulations to better understand observed bloom uniformity and end-of season yield variability and crop quality. Tracking chill portions is helpful to make decisions on the use and application timing of rest breaking agents.

What actions should growers take to weather the dormancy months?

MC: Perform orchard sanitation to prepare the orchard for next season’s crop. Dead and dying branches and unharvested “mummies” provide inoculum sources for pests and disease. Remove dead and dying branches as well as nut mummies from the canopy.

Survey weeds to evaluate the previous year’s management program success and shortfalls, select appropriate herbicides for weed species.

Irrigation system inspection and maintenance are essential to maintaining distribution uniformity and overall efficiency of the irrigation system. Check for leaks and replace clogged emitters, backwash filters, and flush lines, and amend the water with the appropriate materials to get the system in good working order for next season.

Look at yield, tree leaf and nut hull nutrition analyses to construct a nutrient management plan for next season.

How important is the dormancy period?

MC: Research results on rest breaking agents, clay and other light refractive materials are mixed. Winter chill accumulation progression has shifted in recent years. Historically, the majority of chill accumulated in early winter (November and December) with less accumulation in late winter months (February).

Climate shifts in recent years have driven warmer temperatures in the early winter months, with more chill accumulation observed in late winter. Although chill portions for the most part have been adequate in recent years, many questions remain about the use and timing application of oil and newly registered rest breaking agents like hydrogen cyanamide.

How vital is winter sanitation for management of insect pests and other things?

MC: Very important to control navel orangeworm (NOW) a major pest of almond and pistachio. Shake trees as soon as possible to remove unharvested nuts and mummies from trees, then shred or disc them under to reduce overwintering sites. Dead and dying branches and nut mummies provide inoculum sources for diseases like Botryosphaeria in pistachio, almond and walnut.

How should growers ensure their trees are healthy and vigorous during the winter?

MC: Soil sample to determine what soil amendments may be necessary to reduce salinity and improve drainage. If possible, plant a cover crop or apply mulches like wood chips or nut shells to protect the soil in the event of major rain and flood events. These practices will protect the soil structure at the surface and promote drainage.

How necessary are foliar feed and irrigation during the winter?

MC: Micronutrient deficiencies are very common. Fall applied zinc and boron foliar applications prior to leaf fall can be helpful to make sure the tree has adequate levels prior to bloom the following season.