David Doll3 CommentsDecember 23, 2020Horticulture

Tracking Winter Chill in Fruit Growing Regions

Written by Franz Niederholzer1 and Kitren Glozer2 1UC Farm Advisor, Sutter/Yuba Counties, 2Associate Project Scientist, Department of Plant Sciences, UC Davis “Is it a good chilling year?”  That’s a common coffee house question this time of year in fruit and nut growing regions.  The amount of chilling a perennial crop accumulates in a given winter will influence bloom conditions – the most crucial time in a crop season.  Less chilling than a certain tree crop requires can lead to an extended bloom; too little altogether can result in bud death and drop in some crops like apricot and sweet cherry.  ‘Good chilling’ (more chilling than the minimum required) can produce a very short bloom season, or ‘snowball bloom’.  Chilling models can provide growers and their advisors with key information to time dormancy-breaking materials (hydrogen cyanamide, oil, etc.) to manipulate bloom to improve or maintain yield and quality in regions where local chilling is marginal for a certain crop.  Climate change may make achieving critical chilling more important in years to come.  In this article, we’ll briefly review chilling and chilling models.  Deciduous perennial crops break bud in the late winter or spring after a certain amount of cold weather (chilling) followed by a certain amount of warmer weather.  Think of this process as a relay race.  The chilling is the first leg of the race, and the heat accumulation is the second leg.  Bud break is the finish line.  The length of each leg of the race depends on crop and variety.  The weather during the race influences the runner’s speed.  Good chilling weather speeds up the chilling leg, warmer weather can slow it down or even stop it.  Cool weather on the warming leg slows the progress towards bloom.  Since most perennial crops are not native to North America,

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David Doll0 commentsNovember 29, 2020General, Horticulture

Factors to Consider when Determining Honeybee Hive Needs for Almond Orchards

Determining the number of hives to rent for an almond orchard can be challenging. With a strong reliance on honeybees for pollination, placing too low of number of hives and bees can reduce crop potential, especially in inclement weather, while placing too many increases operational expenses. To determine the proper hive strength for the almond orchard, the following factors should be considered: Varieties present within the orchard Age of the orchard Strength of the hives contracted Crop insurance requirements Anticipated weather for the orchard’s production area; Presence of other pollinators. Almond Varieties within the orchard. All almond varieties benefit from having pollinators present during bloom. In California and Australia, the primary varieties planted are ‘Nonpareil’ and the selected compatible, pollinating varieties. Since these varieties, as well as others (e.g.’Butte’/’Padre’), require cross-pollination to set a nut, bees are required to maximize orchard yields. Due to the requirement for cross-pollination, the recommendation by the University of California has been to place two 6-8 frame hives per acre (5 hives per ha) to maximize pollination (Micke, 1996). In Europe and more recently in California and Australia, self-pollinating almond varieties are present. These varieties do not require pollen from a compatible variety to fertilize the flower. In these orchards, bees are not required to set a commercial crop, but they have shown to increase yields. In Europe, studies have shown yield increases between 5-20% amongst European varieties. In California, the presence of honeybees has shown to increase yield by 20% or more within ‘Independence’ (Saez, et al, 2020).  These studies indicate that bees should be placed to optimize pollination, but suggest that the number of hives per acre can be fewer. In Europe, 1-1.25 hives/acre (2-3 hives/ha) are common stocking rates within orchards that utilize bees. This may be a reasonable range to consider

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David Doll0 commentsNovember 15, 2020Technology

Technology Corner: Questions to Ask Ag Tech Companies before Committing

Over the past 12 years, I have worked with several agricultural technology companies who have been interested in working within tree nuts. Companies have focused on a variety of issues, including water, bees, and aerial imagery. Some ideas have been great and have gone on to develop into successful companies. Others have failed to execute the idea or have overestimated the need within the industry. As I have shifted my role into farm management, I was overwhelmed with ag tech options. In reviewing, I found myself asking several of the same questions, regardless of the company and subject matter. Some of them may seem obvious, but they are also questions that can be easily overlooked. They are provided below. Please note that some contain multiple questions which help explore the line of inquiry. How does the technology work and how does it vary from the current market options? What hardware needs to be bought to fully integrate the system? Can hardware components from other companies be utilized with the system? What is the deliverable of the technology? What variables are being measured or recorded? How are these measurements developed into a recommendation? Is there any crop-specific research available to support the analysis utilized by the technology? Where were these studies performed? How many studies have been conducted and by whom?Note: There are many measured variables that may not have relevance to the crop or farming operation. Determine your priorities before meeting. Also, many companies state they are utilizing “machine learning” for developing recommendations. Even so, the “machine” needs to be taught by someone. Making recommendations off averages will lead to problems, and at best, an “average orchard.” Who are the competitors? What does this platform/hardware provide that they do not? What are the unique features that this company is offering?Note:

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David Doll3 CommentsOctober 26, 2020Insects

Field Note: Early Leaf Drop in Almonds from Peach Silver Mite

Written By Cameron Zuber, Research Assistant at UCCE Merced, Graduate student at UC Merced. In the middle of October, a second leaf almond orchard in Parlier, CA presented with a lot of leaves on the ground in the ‘Sonora’ pollinator rows. It was a bit early for the trees to enter dormancy and deficient irrigation was not performed as the orchard was too young to have been harvested this year. Upon closer inspection the leaves on the trees seemed to indicate a pest or disease issue. Early leaf drop in almonds is a concern as it may impact the flower buds that are developing on the tree which could then impact the vigor of the bloom and overall crop yields next year. The browning on the leaf could be an indication of salt burn or leaf scorch (https://thealmonddoctor.com/2014/07/25/salt-burn-vs-leaf-scorch/) and there were some leaves that had rust present (https://thealmonddoctor.com/2010/04/05/almond-leaf-rust-treat-now-to-prevent-late-season-defoliation/). However, the splotchiness of the browning did not seem typical of salt burn or leaf scorch and the rust was not prevalent enough to cause this degree of leaf drop. The symptoms seemed more serve on the ‘Sonora’ trees, but the ‘Nonpareil’ trees were showing similar symptoms though less sever. Another odd symptom were the leaves seemed to have a silvery color which became more apparent when looking through a hand lens and when compared to a neighboring block’s leaves that were a healthy color. The combination of splotchy browning and a silvery color started to indicate a potential culprit for the early leaf drop. Browning is a symptom of rust and a silvery color indicates thrips or leafhopper damage but having both indicated something else. Looking through a strong hand lens showed the presence of peach silver mite (Aculus cornutus). Peach silver mite can be distinguished by their teardrop body shape

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David Doll4 CommentsSeptember 28, 2020Horticulture

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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David Doll0 commentsAugust 31, 2020Horticulture

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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David Doll0 commentsAugust 6, 2020Technology

Technology Corner: Q&A w/Tule Technologies

EDITOR’S NOTE: This entry is part of a series to highlight a new technology related to almond and tree nut production. The question/answer format is set to focus more on the technical aspects and application of the technology. In many articles, I discuss the importance of irrigation. With that in mind, I though I would reach out to a company that assists with irrigation scheduling based on site-specific data: Tule Technologies. Thanks to Valerie Bednarski for taking the time to answer my questions. Tule is an irrigation technology that determines site specific water use for a specific crop. How does this technology work? Tule measures the actual evapotranspiration (ET) of your orchard. We are able to do this using the Surface Renewal Method that was developed at the University of California at Davis (Paw U et al. 1995; Snyder et al. 1996; Shapland et al. 2012a and 2012b; Shapland et al. 2014). ET is the process of evaporation from plant and soil surfaces and from within plant tissues (i.e., water movement through stomata). In most modern agricultural systems, ET is the dominant process of water loss from a field. (Editor’s note: more info on ET here) What equipment is installed, and resources are used to determine water use? The Tule Sensor is installed in the orchard and is positioned above the canopy. The sensor is able to measure the amount of evapotranspiration from the orchard based on air movement.  As the wind moves over your orchard, it picks up the water that transpires from the trees and carries it to our sensor. This is how we are able to measure the crop water use over a broad area. An installed pressure switch is fitted to the irrigation system. This provides a direct measurement of irrigation durations. Using site specific irrigation specifications,

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David Doll4 CommentsJuly 19, 2020Irrigation

Regulated Deficit Irrigation: Is it appropriate for your operation?

Regulated deficit irrigation is the practice of reducing irrigation to obtain some type of desired stress level. This practice is often used during the initiation of the hull-split period to reduce hull-rot strikes. It also has been utilized during periods of water shortages to save 5-15% of the seasonal water use of almond. Due to the limited effect on yield, as well as the benefits, it has been advocated for application within orchards by the University and industry (including myself!). This practice, however, can have negative impacts when applied incorrectly and should only be used if deemed appropriate. In theory, this practice is easy to apply. Water application rates should be cut to achieve -15 bars stem water potential for two weeks preceding the onset of hullsplit (e.g. Blank split). This stress should be maintained at this level for this period. At the end of the two weeks, regular irrigation resumes and the orchard prepares for harvest. The difficulty in application has everything to do with accurately monitoring plant stress. Every orchard and orchard practice creates a different approach in application. For example, assuming similar irrigation levels, stress levels achieved in a mature orchard planted on sandy soil will occur in a shorter time frame than an orchard on a heavier clay loam. Every orchard site requires careful monitoring to determine when to cut and resume full irrigation. I have observed numerous orchardists apply tree stress only to see a reduction in kernel yield. This is due to ongoing gains in nut weight that occur between the onset of hull-split and harvest. If the tree is significantly stressed during this period, the conversion of carbon to fats is reduced, impacting the final crack out percentage. One closely monitored orchard in which I worked, demonstrated a 10-15% reduction in kernel weights

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David Doll0 commentsJune 28, 2020Insects, Technology

Technology Corner: Spear-Lep w/Vestaron

EDITOR’S NOTE: This entry is the first in a new and (hopefully) ongoing series to highlight new technology related to almond and tree nut production. The question/answer format is set to focus more on the technical aspects and application of the technology. Since we are approaching hull-split, I thought a reasonable place to start would be with Vestaron, a company which recently released a new class of insecticides.Thanks to Noel Cornejo for taking the time to answer my questions. Question (Q): Spear-Lep is a new group of insecticides that has been shown to be effective on lepidopteran pests, such as peach twig borer, codling moth, and navel orangeworm. What is the active ingredient and how does this product work? Answer (A): The active ingredient is an insecticidal peptide called GS-omega/kappa-Hxtx-Hv1a. It was carefully optimized to target the nicotinic acetylcholine receptor in the insect nervous system, but at a receptor site distinct from Spinosad and neonicotinoids. The end result is paralysis of the lepidopteran larvae that ingest it. Q. Is this product directly toxic to insect pests? Or does it have to be consumed? How is the activity on developing larvae (may have been answered above)? A. For lepidopteran pests Spear works through ingestion. Extensive studies confirm activity against neonates as well as later instars of all species tested to date. At high v/v concentrations, Spear works though topical contact against smaller, soft-bodied pests such as mites, thrips and whiteflies. Q. How is this product different from what is currently on the market and is there any efficacy data comparisons among the various products on the market?  A. This novel class of insecticidal peptide is the first of its kind. Identified in nature, and then optimized painstakingly in the lab, Vestaron’s peptide insecticides are designed to target neuromuscular receptors proven through

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David Doll8 CommentsJune 28, 2020Horticulture, Insects

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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