David Doll0 commentsJanuary 29, 2020Horticulture, Irrigation

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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David Doll0 commentsDecember 8, 2019Irrigation

Water Meters: Formatting the Data for Use

Water meters are a necessary tool to determine water applications to the orchard. Having access to this near-real-time data can provide insight into the irrigation practices by helping determine if the proper amount of water was applied to a block. Furthermore, a deeper analysis of this information can assist with managing field variability by improving distribution uniformity and even estimating yield. Before diving deeper into the data from water meters, it is important to format the data into a consistent value across the operation. Even though water meters are sold in all shapes and sizes, there are generally two types: totalized flow (reporting the total amount applied to the field) or current flow meters (reporting the current flow of volume). Knowing which type of meter is present within the orchard is required to understand the application of water to a particular block. Due to manufacturing differences and meter types, data may be reported differently. Common units used within the United States are gallons (gal), acre inches (a.i.), acre feet (a.f.), cubic feet per second (CFS), or gallons per minute (GPM). Within the rest of the world, the metric system is used and reporting is either in liters or cubic meters (cbm) with flows reported as liters or cubic meters by time (second, minute, hour). Totalized meters will report as a number of a particular unit applied. This value has to be subtracted from the previous measurement to determine how much water was applied over a period. Current flow meters report the flow of water and reports it as a measurement over time (e.g. gallons per minute). This data has to be multiplied by the irrigation set time to determine the amount of water applied. After the initial data is collected, it is then needed to format it into a common

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David Doll0 commentsNovember 7, 2019General

Tree Loss Value Calculator

Unexpected tree loss happens. Whether it involves flooding of a field by a broken pipe, an inattentive driver, a natural disaster or some other circumstance, tree loss can occur within an operating orchard. A common question is how to value trees that have been damaged or lost due to various circumstances. Valuing trees is not as straight forward as it may seem. Many would assume that to replace a tree, the expenses are limited to the removal, clean-up and replanting of the tree. Although this is true, this does not represent the full investment of that tree. To fully account for the loss, applied operational expenses and lost yield must be considered.  These values for yield and operational expenses, however, must also take into account that a replanted tree will grow into maturity, and produce similar yield as other trees within the orchard. This would need to value the lost yield for the first 3 years of growth as well as the increasing yields until maturity. This calculation is not so straight forward. Thankfully, there is a tool to help estimate tree loss. A “Tree and Vine Loss Calculator” has been developed by the University of California Agriculture Resource and Economics group at UC Davis. This simple spreadsheet application provides the ability to enter in specific orchard details to determine the value of the tree(s) lost. It considers the operational expenses applied prior to the tree loss, as well as the replanting expenses and yield loss until the new tree begins to crop. Orchard specific characteristics should be entered into the spreadsheet to provide a better estimate. This includes tree removal and replanting expenses, yields and spacing. Operational expenses are based on the cost studies developed by the University. Since the cost studies are regionally developed, the appropriate calculator should

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David Doll8 CommentsSeptember 29, 2019Diseases

Phytophthora: An Update

As previously written (2009 article and 2015 article), Phytophthora is a plant pathogen of almond trees. This fungal-like water mold is common throughout the various almond growing regions of the world, with 6* or more known species causing disease. When conditions are conducive for infection, the pathogen directly invades plant tissues at the crown or roots, leading to loss of nutrient and water uptake, causing tree decline and eventual death. The rate of infection and tree loss depends on the inoculum present, the choice of rootstock, environmental conditions, and cultural practices that may favor disease. Phytophthora inoculum can be endemic to the orchard area or introduced through a variety of ways. Low levels of Phytophthora probably exist in most soils, but typically are not at the levels or location to cause infection unless there are prolonged conditions favoring disease.  Generally, introduction of inoculum into the area of close proximity to the plant is most likely responsible for infections and tree death. This includes the crown or base of the tree where the pathogen infects the plant just below the surface of the soil. These types of infections are most common and can lead to rapid tree loss.  Root infections, which occur when soils are saturated with water, lead to a gradual decline. Finally, aerial Phytophthora happens when spores are deposited on limbs or in crotches of the trees through dust or flooding, followed by wet conditions (e.g. rain). Surface water is believed to be the major contributor of Phytophthora inoculum in perennial nut orchards. Surveys have found several species of pathogenic Phytophthora in high elevation, upstream waterways of the major rivers in California. Due to the ability of the pathogen to survive in water, this pathogen is probably found in all surface water used to irrigate trees worldwide.  This inoculum

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David Doll4 CommentsAugust 20, 2019Diseases

Almond Shaker Damage

Shaker damage is commonly observed across orchard operations. This damage occurs when the force of the shaker is greater than the strength of the bark, causing it to tear away from the tree. The obvious damage not only impacts tree vigor, but also provides an opportunity for infection by wood canker fungi which can kill the tree. If the shake is properly timed and executed, shaker damage can be greatly reduced (and even eliminated) within an orchard. A common misconception is that trees that are kept too wet during the harvest period will be damaged by the harvesting process. Interestingly, this has never been supported in research nor found to be consistently true across operations. Research in the mid 90’s by Gurusinghe and Shackel found that withholding irrigation during July through harvest did not reduce bark damage of the trees. To further elaborate, they found no difference in bark strength with respect to shaker damage for almond trees grown under various irrigation treatments. Irrigation treatments included a wet treatment and dry treatment, in which mid-day stem water potential (SWP) was maintained at -9 bar and -20 bar, respectively, through the month of July/August. Despite this range in tree water status, both treatments exhibited the same gradual increase in bark strength through July and August. Based on this, the researchers concluded that water stress did not influence the timing or rate of tree bark strengthening. Based on the lack of direct effect of moisture status on tree bark strength, it is thought that the damage observed in wet areas of the orchards is most likely due to the delays in ripening. Research has found that decreased water stress (Goldhamer and colleagues, 2006) and high nitrogen status (Saa and colleagues, 2016) both  delay ripening. These trees, when shaken at the same time

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David Doll0 commentsAugust 8, 2019Diseases, Field Notes

Field Note – Powdery Mildew of Almond

Written by Cameron Zuber, UCCE Merced County Some interesting almonds came into the office and, no, this is not a setup for a joke. In the middle of July, some almond fruit nuts from Le Grand, CA were brought into the Merced County UC Cooperative Extension office. There were various signs of possible pest damage and disease infection. These included black growth inside the hull indicating possible Rhizopus stolonifera fungus which may lead to hull rot; grayish-black spots indicating scab (Cladosporium carpophilum); and gumming which may indicate bacterial spot (Xanthomonas arboricola pv. Pruni), anthracnose (Colletotrichum gloeosporioides), or bug feeding. However, the greatest amount of damage were odd areas of russeting and cracking on the hull. After speaking with person who brought in the samples, there was not any indication of leaf or shoot die back near the nuts which starts to rule out hull rot and lab tests did not show any fungi that would cause hull rot. Lab test also showed some instances of almond scab growths, but none of these pest or disease symptoms were at a level to be extremely concerned about. Also, none have been shown to cause the odd cracking on the hull, so what was the cause, should you be worried about it, and how do you fix it? The cause was found through some digging and a lot of help from farm advisors and plant pathologists. It was determined that the cause was most likely a false powdery mildew (or powdery mildew-like) fungus of the Acremonium species. Normally these organisms live on dead or decaying organic matter (i.e., saprophytes), but do occasionally infect plant material and, for almonds, result in the russeting and cracking seen in the above fruit nuts. It is called “false” or “like” powdery mildew because it shows similar symptoms

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David Doll2 CommentsJuly 30, 2019Horticulture

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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David Doll4 CommentsJune 30, 2019Horticulture, Soil

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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David Doll0 commentsJune 23, 2019Irrigation

Irrigating almonds through the summer

Almonds require a lot of water during the summer. This is due to the high temperatures experienced and the crop stage of the tree. It is not uncommon for an acre of almond trees to have evapotranspiration rates exceeding 0.30” (or 7.5 mm/ha) per day across the growing regions in California. Regardless of what is believed, almonds are sensitive to water stress during the summer. Moderate to severe stress through June and July has been shown to reduce kernel weights. This has been demonstrated in multi-year and multi-location experiments across California, in which researchers have found that kernel weight begins to decrease once the average mid-day stem water potential (SWP) for June and July becomes more stressed than -15 bars. Kernel weights were reduced by as much as 20%. This reduction is due to the reduction of photosynthate that is being produced and converted to fats within the almond kernel. Based on the risk of crop loss, it would be easy to think, “why should we stress almond trees in June and July?” This is due to the various farming demands of the system. Mild to moderate stress levels during the onset of hull-split have been shown to reduce hull-rot. Shaker damage can be reduced by the reduction of over-irrigation in wet-lying areas. Finally, drier fields make it easier to access with larger equipment, easing harvest processes. Applying tree stress isn’t as easy as reducing or cutting the irrigation duration or frequency. In many cases, excessive stored moisture makes it difficult to readily apply stress. Trees will need to “suck out” this moisture in order to make them more responsive to deficits at hull-split and harvest. Once trees are more responsive, mild to moderate stress levels are easier to achieve by reducing the duration of the irrigation by a few

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David Doll2 CommentsMay 26, 2019Weeds

Newly Planted Orchards: Weed Management

Managing unwanted vegetation is difficult in newly established orchards. Weeds grow fast due to the amount of water, fertilizer and sunlight that is available. Temperatures in the spring and summer often favor weed growth, which can quickly overgrow trees, reducing nutrient and water availability. Furthermore, control is difficult due to the sensitivity of the tree to herbicide damage. These factors make weed control one of the most challenging aspect when developing a new orchard. Most operations rely on post-emergent (aka burn-down) materials for control of weeds in newly planted trees. These products kill the plants that they contact by a number of mechanisms. Burn-down materials, however, have risk in use as drift can damage or kill young trees. This is especially true with glyphosate (e.g. Round-up) which is a systemic herbicide that can persist for a long time within a plant. To reduce this risk, glyphosate should be avoided, and operations should rely on contact materials (e.g. paraquat, oxyfluorfen) for the first growing season. Contact post-emergent products aren’t as effective as systemic products. These materials will require multiple applications through the year as they only kill the top part of the plant. Usually within 2-3 weeks, the plant begins to regrow, and follow-up sprays will be needed. Further management challenges exist for weeds that are “hairy” or have a waxy cuticle. These features prevent the full contact of the herbicide with the plant surface, reducing kill. To manage these variations within the population, coverage is critical. Utilize the upper limit of the label rate of the primary herbicide and make use of any water conditioners to improve efficacy. Increase the volume of water to provide more thorough coverage. This often means that applications are in the 30-50 gal/acre range. Check and replace worn nozzles and perform the required maintenance on

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