By the time you read this, the cards will be on the table for a new season following the wettest, coolest winter since 2019. Add the current economics of nut growing, and 2023 will require another year of careful farming. My goal here is to look at some of the possible areas of focus for this season and early season as I see them, both in the field and in the shop/office. My approach is from a NorCal perspective as that’s my background and experience.
With prices off and costs up, current economics are, to put it nicely, difficult. Widespread almond crop loss due to frost damage last year in the Sacramento Valley makes the year even tougher on many ranches in the area. In conversations with trusted advisors, growers might consider what can be done in a year where all that can be done might not be possible. Of particular concern to growers are practices that support the crop next year, including careful irrigation, nitrogen (N) and potassium (K) nutrition, and pest outbreaks (rust, mites, scab, etc.) that risk defoliating trees at harvest and reducing bloom next year.
There is relatively good news in general (as long as the cool February weather didn’t badly harm almond nut set) as the 2023 season gets off to a start very differently than the previous three drought years. With more chilling this winter than in the last seven, pistachios and walnuts should see good, sharp bloom timing. Cooler March temperatures forecast for the Sacramento Valley should delay in remaining crop bloom compared to warmer springs and biofix timing for many key pests such as navel orangeworm (NOW) and peach twig borer. The extended wet winter of 2022-23 should translate to much lower soil salt (EC, chloride, boron, etc.) levels compared to the last three drought years and deep water available to trees. If rain continues in March, the surface water allocations may come up, providing high quality surface water to growers across the valley.
Almonds
Water
Water is always the place to start. The good news for 2023 is this may be the best spring below ground in years. The soil profile should be full of good quality rainwater to start the season and the salts, built up over the past three drought years, leached away. With good rootstock selection and site prep (laser leveled, berms, islands or bumps), the roots should be in good health (but see following disease section if there are concerns.)
Spring irrigation can be like city driving; often, it’s stop-and-go as variable weather rolls through and orchard water use changes with sunlight and temperatures (summer irrigation is often like highway driving; steady and fast.) Effective spring irrigation requires attention to the orchard and the weather. Moderate orchard water stress can stop critical shoot growth (shoot growth shuts down at -14 bars stress), but excess water can mean saturated soil and stressed roots.
When should almond irrigation start? In general, irrigation should start no sooner than when soil water has been “drawn down” enough by orchard water use (ET) that water applied doesn’t flood the soil (and stress the now active roots.) Keep an eye on the forecast as cooler weather ahead means less orchard water use and the risk that a refilled rootzone won’t be ‘tapped’ as quickly as in warm weather, and the roots (and trees) suffer. I have seen orchards “yellow up” in the spring when a full irrigation goes on ahead of a cool stretch. Note that good cloud cover without rain is enough to shut down ET. When it’s overcast, plants don’t use water; they ‘trade’ water for energy from sunlight, and when there is no sunlight reaching the leaves, the deal is off. As soon as the sun breaks through the clouds, leaves are back in action. Use whatever monitoring tools you are comfortable with to track orchard moisture and time irrigation. Where possible, check your practices with a pressure chamber (see reference at the end of the article). That’s the gold standard in tree moisture status. Soil moisture meters (or a hand auger) helps you know how far a certain irrigation set moves in the soil and dial in the amount of water to use with each irrigation. New, automated tree moisture sensing equipment is beginning to approach field sampling results. Dr. Ken Shackel, UC Davis Plant Sciences, has been comparing several tree moisture monitoring systems.
Nutrition
April is early in the N and K demand window in mature almond orchards. Adequate N and K support nut growth, but excess application wastes money. Since the crop is the main driver of N and K use in mature orchards, early season leaf sampling and lab analysis can help get a sense if demand is high or low. Relatively low levels of leaf N early in the season can indicate a large crop and the need for more N fertilizer. The early leaf sampling window in almonds is 45 days (± six days) after full bloom using the UC Davis April sampling protocol. See details of the sampling and analysis (and more crucial N management info) in the Best Management Practices for Nitrogen booklet from the Almond Board. See page 14 for details on the early season sampling protocol. Private labs have developed their own guidelines for interpreting early season leaf sample results. Talk with your CCA about what is available.
Don’t forget K. Current economics may mean a change in how much K is used, but deficient trees will have less bloom the next year. Use May and/or June leaf sampling to check orchard K status ahead of traditional July samples. Flower formation starts in July/August (preharvest), so it’s too late to avoid yield reduction potential next year from K deficiency this year. How can May or June leaf samples help stave off deficiency later in the summer? Leaf K levels generally decrease from spring to summer (unless summer K fertigation is used.) If May or June samples show leaf K levels are low (close to the adequate/deficiency threshold), fertigating a modest rate (50 lbs K2O/acre) of liquid K fertilizer may be enough to keep the orchard out of deficiency and maintain yield potential next year. A single leaf sample costs about $1 to $2/acre for a 100-acre orchard. Looking to the future, broadcasting almond shells (about 1.5% K by weight) in the orchard may be a way of reducing the K fertilizer bill without harming yield. Shell K is leached into the soil by rains or sprinkler irrigation.
Pests
Talk with your PCA/CCA about disease risk and control options based on current orchard conditions and forecast weather. Disease pressure builds in an orchard, especially spring and summer diseases, so knowing when conditions are risky is key to best disease control. The Almond Board of California, working with UC researchers and Semios, has sponsored a disease prediction webpage that forecasts relative risk of anthracnose, alternaria, bacterial spot and bacterial blast in general regions of the state. See the page at ag-radar.com/almond. The password is Almondboard2022.
Where water stood for days after heavy rains on susceptible rootstocks this past winter and/or spring, phytophthora root and crown rot (PRCR) may be an issue. Talk with your PCA about new and established fungicide options for phytophthora control. Growers now have multiple effective options. See page 37 of the 2022 Fungicide Efficacy and Timing publication for efficacy of registered products.
True bugs (stinkbugs and leafooted bugs) are a growing problem in many regions of the state. Brown spot on harvested almonds is believed to be from stinkbug, especially green stinkbug, which overwinter in almond orchards. Look for barrel-shaped eggs in masses, often on almond hulls. More information on stink bugs is available from UC IPM.
Get ahead of ant damage this spring before the rush of harvest. Ants feed on almonds that have been dropped to the ground to dry. Scout for ants beginning in April to June. Talk with your PCA regarding control options if scouting shows a need.
Could this be a tough year for navel orangeworm (NOW)? Perhaps. We’ll see as the season progresses. Biofix should be weeks later than during the drought due to cool winter temperatures. Keep in mind the worst years for state-wide damage in the last two decades (2006 and 2017) were wet, cool springs with late biofixes (mid- to late April) followed by very hot summers. We’ll see how the summer goes and when biofix occurs, but NOW control for the season is a good topic to discuss with your PCA. Harvest timing is an important tool in reducing NOW damage (but have an ant program in place if scouting finds ants.) In-shell prices are good, but NOW damage standards are tighter than kernels. Finally, NOW control is expensive. Using mating disruption to reduce the population in a region may be one solution and will take coordination with neighbors. The Almond Board has put together an interactive map where almond growers as well as walnut and pistachio growers can share location of orchards with mating disruption and, perhaps, build a larger area where the NOW population can be reduced. See the site at agneighbors.com.
Finally, to save money and reduce pesticide use, get the best coverage when you spray, especially in the summer as the canopy pulls down with a crop (knock, knock) and coverage is toughest. Slow down (2 to 2.25 MPH) and spray both sides of the tree, making sure to spray in opposite directions on adjacent rows (this helps eliminate spray shadow.) Use higher spray volumes when good coverage is needed in heavy summer foliage and direct most of the spray (65% to 80%) through the top half of the open nozzles. When hot weather arrives, spray when relative humidity is above 40%, which often means spraying at night.
Walnuts
Walnut bloom may just be getting started as April begins and this issue hits your mailbox and/or inbox.
Water
Recent research suggests first irrigation in walnuts can be delayed for weeks beyond the traditional start timing with little impact on the trees and water and money savings to the grower. This should be done with the help of pressure chamber readings to track orchard water status and using an irrigation threshold of no more than -4 bars. With walnut prices where they are now, this approach may be helpful.
Much of what was for almond goes for walnuts as well, including the fast/slow nature of spring irrigation in some years with cool spring weather.
Pests
Walnut blight is a major pest of walnut, and the traditional approach to managing blight is a combination of two of the three materials copper, EBDC fungicide (Dithane, Manzate, etc.) or the new bactericide, Kasumin®, for both highly effective disease control and resistance management. Using just copper risks resistance buildup. Mixing copper and Dithane or Manzate provides excellent blight and anthracnose control along with decent levels of Botryosphaeria (Bot) control. Copper alone provides slightly less blight efficacy (4/5 not 5/5 in the UC guide) and no anthracnose or Bot control. Growers must balance cost with control.
Phytophthora damages walnuts, too. If all or part of the orchard has been flooded this winter or spring, talk with your PCA about control options.
Nutrition
Nitrogen demand per acre in walnut is less than almond. With a crop removal of approximately 30 to 35 lbs N per ton of in-shell walnuts plus 5 to 8 lbs N to support new shoot growth, about 120 lbs N/acre is used by a 3 ton/acre crop. Adjusted for 75% nutrient use efficiency (N in the tree/N applied), this means 160 lbs N/acre should be applied to deliver 120 lbs N/acre to the orchard. How much fertilizer does that come out to? For UN32, 160 lbs N works out to 500 lbs (141 gallons) of UN32. Walnut tree N use is constant through the summer, so the recommendation is 25% of the annual budget applied each month from May through August. In the case of the example from above, this works out to 40 lbs N (11.3 gallons UN32)/acre/month from May through August.
Potassium is important for productive walnut orchards, and K should be added to keep July leaf K levels at 1.5% K or above. K demand in walnut orchards is generally less than in almond orchards, partially because hull pieces drop through the walnut pickup chain and return K to the orchard and they degrade.
As the season progresses, the crop size picture in different nut crops will be clearer, driving planning and decisions. Best of luck this season to all in the California nut industries.
Resources
Pressure chamber for irrigation: sacvalleyorchards.com/manuals/stem-water-potential/using-a-pressure-chamber-is-worthwhile/. This page contains links to more, free, information from UC research, much of it funded by the Almond Board of California.
Nitrogen: almonds.com/almond-industry/orchard-management/soil-quality-and-nutrients/nutrient-management. This page contains links to more free information from the Almond Board of California, much of it produced by UC researchers with ABC funding.
Disease management: ipm.ucanr.edu/agriculture/. At the bottom of this page is a link to the free 73-page document from UC IPM titled, “Fungicides, bactericides, biocontrols, and natural products for deciduous tree fruit and nut, citrus, strawberry and vine crops in California, 2022.”
Stink bugs: ipm.ucanr.edu/agriculture/almond/stink-bugs/
Ants: ipm.ucanr.edu/agriculture/almond/ants/
Almond Rootstocks Information from UC: fruitsandnuts.ucdavis.edu/crops/almond
