Should California consider European Almond Cultivars?

Over the past few years, I have visited several almond orchards across Spain and Portugal that are producing European cultivars of almonds. These orchards are of all shapes and planting methods, including super high density, modern high densities (115-180 trees/acre), trees with an upright, bushy, or semi-upright structure, and various pruning methods. Cultivars planted included releases from the 1970’s through releases from the past ten years. These varieties are characterized by their hard-shell/low kernel turnouts, self-fertility, later blooming, and higher fat content. Production in these orchards is highly varied. Production within most plantings is less than what is expected in California (i.e. 2000 lbs/acre is a good yield), with ranges observed from 1000-3000 lbs/acre. It is hard to determine the reason for such a wide range in yields because of the number of variables involved. Many plantings are grown in water-limited environments (~60-80% of full irrigation), have varying development practices, as well as shorter growing seasons. Furthermore, nearly all the European cultivars have a lower crack out (~30-40% in comparison to 45-60% for California varieties), which impacts yield. Unfortunately, direct comparisons to “California” cultivars are few. This prevents direct comparisons of bloom timing, production potential, and production operational expense. European cultivars, however, may have some characteristics that would be useful within California production systems. These characteristics include: Self-fertility. Due to the ability for the pollen to pollinate and fertilize flowers on the same tree, these cultivars provide several advantages to most CA type orchards. This includes the planting of solid blocks, reduced bee requirements, and easier irrigation management during critical times. Beehives do seem to provide a yield response, and it is estimated that 0.5-1 hive/acre would be needed to maximize yield. The release if the California cultivars ‘Independence,’ ‘Shasta,’ and other soft-shell, self-fertile almond cultivars provide these similar benefits.

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Stuck Nuts: Varietal Influences

Nuts can be hard to remove during harvest for a number of reasons. They include hull rot, boron toxicity, inconsistencies in ripening, and poor irrigation practices. Causes for each of these issues have strategies that can be implemented to reduce the problem and have been highlighted in previous posts. When discussing challenges in nut removal, one major factor that is often overlooked is nut variety.  Due to differing growth habits of each variety, good nut removal may be difficult to achieve at varying points of orchard establishment. For example, Aldrich, Independence, and Wood Colony can be difficult to shake during the establishment years, while Padre is a challenge at maturity. These differences are due to tree architecture and the location of the developing nut. Tree architecture impacts nut removal because the process requires the transfer of energy from the shaker. Trees that are tall, upright, and tend to bear at the end of the limb have a lower amount of energy that is transferred during shaking. Due to the height and proximity of the limbs to the central axis, these trees often require different shake patterns or procedures to achieve the optimal removal of >99% of the nuts within the tree. Pruning to minimize height may reduce the problem for a year or two, but once the wood regrows, often redeveloping with a very vertical structure, the shaking difficulties will return and increase. It is best to try and develop these trees with a wider structure at orchard establishment. Cultivars that fall within this category include ‘Padre’ and ‘Aldrich.’ Positioning of the nut also impacts shake efficiency. Young trees that tend to bear a lot of nuts on the primary wood are very difficult to shake. This effect is two-fold: the closeness to the central access prevents energy transfer, while

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Almond Gumming: When is it a problem?

An inquiry was received regarding almond gumming. The farmer observed clear gum exuding from multiple nuts in the fields. The concern was regarding the potential of a severe leaffooted plant bug infestation, and if an insecticide should be applied to reduce the damage. Generally, there are two types of damage that cause hull gumming: internal and external tissue damage. Internally, damage to the vascular tissues that surround the developing nut can cause gumming. This type of damage is often due to an enlarging nut that puts pressure on the hardened shell, leading to a disruption of the vascular bundles between the shell and the hull. Once the damage occurs, the exuded gum exits through the weakest point of the nut, which is often in line with the suture. This commonly occurs with varieties that have large kernels or in years with cooler than normal temperatures which provide conditions for larger kernel growth. It is not an issue as it does not affect harvest or kernel quality. External damage that causes gumming is more concerning. This damage can be caused by physical damage or by insects. Within orchard settings, knowing the weather history or location of the damage can lead to the diagnosis of the cause from abiotic issues (e.g. hail, equipment, etc). Damage from biotic causes is typically more random as it is usually caused by Hemiptera insects (e.g.true bugs), which include stink bugs and leaf-footed plant bugs. These types of insects have mouth parts that can pierce the hull and cause nut damage and loss. If the feeding is early enough in the season it can kill nuts, if after shell-hardening, feeding can still damage or discolor the kernel. The distinguishing characteristics to determine the difference is the location of the gumming. If occurring after shell hardening and in-line

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2020 Bloom Considerations

As the 2020 almond bloom/crop year begins, there are several considerations to keep in mind. These points may be useful to help understand observations from the field as well as provide an understanding of any direction received. Nut set. Flower set percentages will vary from year-to-year. For mature trees, about 20-30% of the flowers will set while younger trees will be slightly higher. Even though this is low, crop loads are still high due to the number of flowers that are in each tree. A mature tree will have an estimated 35,000-50,000 flowers, depending on tree size. For more information on this, please see this article: https://thealmonddoctor.com/2016/03/07/almond-set-and-nut-drop/ which discusses the results of a tagging study which followed the development of almonds through the season. External factors greatly influence the set percentages. Crop load from the previous year impacts the amount of energy available for flower formation and bloom. High yields from the year before will reduce the number of flowers that will set nuts. Poor weather conditions can reduce bee flight hours, kill flowers in freezing temperatures, or promote disease. The period of weather risk extends into the fertilization period, which continues for several weeks. Keep in mind that the crop is susceptible to frost and diseases as long as there is a risk of frost and rainfall.   Several factors can be mediated by good farming practices. These include the presence and strength of pollinators (usually honeybees), post-harvest practices, and nutrient deficiencies. Honeybees are required for varieties needing cross pollination (most CA orchards – 2.0-2.5 hives/acre) and recommended for self-compatible varieties (0.5-1.0 hive/acre, although the exact number is unclear). Stronger hives (8+ filled frames) are essentially an insurance policy for poor weather conditions. Hive numbers and placements should take into account the weather. Post-harvest treatment of the trees is

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Influence of water availability on orchard spacing and development

Orchard canopy coverage has been shown to correlate with yield. As canopy size increases, more sunlight is intercepted by the leaves. This leads to the production of more energy that can be directed to the tree, leading to more growth, and therefore more crop. Correlation of intercepted light at mid-day (PAR) and kernel yield per acre. Research conducted by Lampinen, et al. What is often forgotten is the most critical to canopy development: water. Without access to water, tree canopy growth will slow or stop due to the reduction of gas exchange and photosynthesis, leading to smaller canopy size. Water is generally limited within an orchard system by either supply (e.g. reduced access to irrigation water) or delivery issues (e.g. irrigation engineering or water infiltration issues). To complicate this even further, water availability is not necessarily simply the amount of irrigation water available per area of orchard. It also takes into account rainfall that has been stored within the soil, general water availability, system engineering and distribution uniformity, and water infiltration rates. Limitations in any of these will lead to a reduction of the tree’s available water. Work by researchers in California has shown the correlations of canopy coverage with yield. This research was performed by gathering the amount of light intercepted at mid-day and comparing it to measured yields within orchards in California. This work has identified that high-producing orchards tend to alternate around 50 kernel lbs for every 1% of light intercepted, giving a theoretical maximum yield of 5000 lbs/acre.  Since it takes water to develop the canopy, this correlation can be also be extrapolated to water use: every percent of the tree’s water needs met will provide roughly 50 kernel lbs of crop in California’s growing conditions. An orchard with >80% light interception requires full irrigation to

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Shaking Almond Trees: When to Start

The start of shaking almond trees will soon begin in California, as well as the rest of the northern hemisphere. This process utilizes a piece of equipment which clamps to the tree and applies a vibrational force. This energy is transferred to the nut. The vibration moves the nut, which causes the tissues to disconnect at the abscission layer. Nuts then fall to the ground to finish the drying process. As the nut matures, a few physiological changes occur. Maximum nut weight for ‘Nonpareil’ occurs sometime around the first week of August. Prior to this point, kernel weight is accumulating as the sugars are turning into fats and proteins within the kernel. This conversion is what gives the kernel weight after drying. As this is happening, the abscission layer forms between the nut and the peduncle (also known as the separation zone). As the nut continues to mature, moisture within the hull will decrease and the abscission layer will become more apparent. Generally, nuts become easier to shake as they mature, but this isn’t always the case. Increased fertility and irrigation rates have increased the variability of ripening. Also, certain varieties (‘Independence,’ ‘Padre,’ ‘Wood Colony,’ ‘Price’ and ‘Monterey’ to name a few) are difficult to shake due to the incomplete formation of the abscission layer or the structure of the tree’s canopy. Diseases or toxicities (e.g. Hullrot and boron toxicity) may also make it difficult to remove nuts as gumming may cause the nuts to stick to the tree. Lastly, hull-tights, or nuts in which the hull has completely dried may not be easily removed due to the lack of weight during the shaking process. These factors will increase the mummy counts within the trees, requiring poling or a second harvest, or a more effective sanitation program. Due to these

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Cover crop research review: How can it help almonds?

Cynthia Crézé (1), Jeffrey Mitchell (1), Andreas Westphal (2), Danielle Lightle (3), David Doll (3), Mohammad Yaghmour (3), Neal Williams (4), Amanda Hodson(4), Houston Wilson (5), Kent Daane (6), Brad Hanson (1), Steven Haring (1), Cameron Zuber (3) & Amélie Gaudin (1) Department of Plant Sciences, University of California – Davis Department of Nematology, University of California – Riverside University of California Agriculture and Natural Resources – Cooperative Extension Department of Entomology and Nematology, University of California – Davis Department of Entomology, University of California – Riverside Department of Environmental Science, Policy and Management, University of California – Berkeley Although cover cropping is compatible with almond production and is often implemented in other orchard systems, this practice has never been widely implemented in California. The potential benefits are recognized by growers, especially their value for pollinator forage and soil health but operational concerns, lack of cost-benefit analyses and unclear best management practices have hampered wide adoption. As cover cropping can provide significant sustainability benefits, there is an urgent need to assess and develop feasible and beneficial cover crop systems for California almond production. Here is some insight gathered by a research team assessing the impacts of multiple cover crop management strategies on: 1) soil health, 2) water use and dynamics, 3) bee visitation and pollination, 4) weed and pest pressure (NOW) and 5) almond yields in four orchards across the Central Valley precipitation gradient. Cover crop research trial in almond: Project website: https://almondcovercrop.faculty.ucdavis.edu Design: Three commercial orchards in Corning (Tehama county, 2nd leaf), Merced (Merced county, 16th leaf) and Arvin (Kern county, 16th leaf). One experimental station: Kearney (Fresno county). Two cover crops: Soil Mix (2 legumes, 2 brassicas & 1 grass), Pollinator Mix (5 brassicas, Project Apis M – https://www.projectapism.org/pam-mustard-mix.html) Compared to resident vegetation & to bare soil. Cover

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Timing Fungicide Sprays: Thoughts for a Wet Spring

Improper timing of fungicides wastes money and leads to crop loss from disease. Over the years, I have seen several disease epidemics that were due to the improper timing of a fungicide spray. These were observed in both wet and dry years, indicating the difficulty and general misunderstanding of disease and spray application timing. Proper timing of fungicide applications is difficult. Operational constraints in applying fungicides leads to mis-timed (too early, too late) or poor applications (every other row, applying too fast). This is often a function of equipment availability, whether by grower/operation or custom applied spray. Add to this aspect the various layers of fungicide availability and delivery timing, the changing pathogens and disease conditions, as well as the general misconceptions of various diseases, it is very easy for problems to occur. In order to control diseases, as advocated in earlier postings, it is best to design a fungicide plan prior to the start of the season. This provides the opportunity to review reference materials and determine which fungicides are best for differing stages of the crop. This plan also creates the opportunity to provide options for differing modes of actions at each timing to help with pricing, and reduces the burden of having to put the plan together when the season has started (and there are several other demands). Personally, I like to design the plan for a wet year and remove fungicide timings if dry conditions occur. An example of a plan with different modes of actions can be found here. Diseases don’t just occur. They require a susceptible host, the presence of a pathogen and suitable environmental conditions. For most almond foliar or bloom diseases, the pathogen is throughout the environment and most of our varieties are susceptible to one disease or another. The largest variable

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2019 Almond Bloom Considerations

Almond bloom is just around the corner. This “start” to the season is an important period for almond production as flowers require reasonable weather conditions for pollination, fertilization, and eventual fruit set to occur. With that in mind, below are a few considerations for this period. Rain or conditions favoring dew can increase the amount of disease. Pathogens affecting almond flowers are ubiquitous in the environment, and therefore the condition that influences infection are periods of leaf wetness. Fungicides should be applied to protect the flowers from rain-splashed spores and subsequent infections. Newer class fungicides can move into the upper cell layers of the flower and kill infections, but this “reach-back” potential only provides about 2-3 days of “cure” after a rain event. Start the spray program with fungicides that are most effective for blossom diseases, but provide limited protection for petal fall and spring-time diseases. This typically includes the FRAC groups 1 and 9. As bloom progresses into petal fall, other fungicides should be considered to manage anthracnose, green fruit rot, shot-hole, and scab. FRAC groups 3, 7, 11 or combinations of these products should be considered. Remember to rotate away from fungicide FRAC groups used in previous sprays. This will help reduce the formation of resistance within pathogens, increasing the “shelf life” of a fungicide. To assist with this, especially if rainy conditions are expected, consider utilizing a broad spectrum material at petal fall or shortly after this period to provide the ability to use strobilurins and DMIs (FRAC 11 and 3) for scab and rust control. Some good rotational, broad spectrum products include chlorothalinil (FRAC M5), Ziram (M3) or Captan (M4). Don’t forget about the bees. Honeybees are brought into the orchard to provide pollination services – a requirement for production for most California type almond varieties

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Pruning Almond Trees

Pruning recommendations vary by the farmer, consultant, and even the University researcher. Some advise to prune trees hard to regenerate growth (not so much in CA anymore), some suggest that only a few limbs be removed annually, while others advocate throwing away the pruning shears. With these differences in opinion, what is the proper way to prune a tree? Young Orchards: Research has shown that reduced pruning on younger trees can lead to larger, earlier yields. This is mostly due to increased canopy that is able to produce crop. Some research has found early benefits of leaving young trees unpruned, but have found that over time, these branches will split when the crop load begins to increase leading to yield loss. Hence, some structuring of first and second leaf trees is recommended to address tight branch angles and close proximity of scaffolds, which leads to included wood and weak branches. Scaffold selection on young trees should be based on growing conditions. There is no set number that is ideal, and a farm level decision should take into account tree vigor, spacing and management practices. Heading the trees higher at planting (42” or higher) will provide more opportunity to select scaffolds, but will increase pruning time. Heading the trees too short may lead to issues with shaker head placement at maturity, leading to more bark damage. After the first year of growth, select scaffolds with distance in between and avoid scaffolds on the same plane and height of the trunk of the tree. By spacing the scaffolds vertically and around the tree, the growing limbs will be better attached, leading to less breakage. Remove steep angled limbs as these are often weaker. Limbs with a 45-60 degree angle are ideal. Avoid hard heading cuts as cutting the tree back too hard

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