Almond Irrigation Scheduling: Deciding on a Crop Coefficient

Crop coefficients for almond have been studied for nearly 50 years. These values indicate the ratio of water use of almonds in comparison to fully irrigated grass (ETo). Values less than one indicates that almonds are using less water than grass at that period while values greater than one indicate a higher water use. This ratio needs to be multiplied by the daily ETo, whether actual or estimated, to determine the water usage for almonds. The crop coefficients provided below are research derived. Differing techniques have been used to develop the coefficients. Some rely on a “water-balance” method in which soil moisture levels are monitored and maintained to match water use. This method has been utilized by many researchers across the world and has formed the foundation of most irrigation research. A more exact method of this technique involves the use of a weighing lysimeter, which is a giant scale that measures the amount of water used by the tree. Due to a minimal number of lysimeters in the world, studies have not been performed until recently and the results for mature almond water use has yet to be published. Outside of the “water-balance” method, there are newer technologies that have been used to develop crop coefficients. These techniques utilize fluctuations of canopy temperature that occur from transpiration loss.  These measurements, when taking into account solar radiation, wind, and ambient air temperature and humidity, can be used to back-calculate the water loss. This method is known as “eddy covariance.” When reviewing the differing crop coefficients, it will be clear that the general trend is greater water use. Some of the upward trend is due to a change in irrigation practices and orchard canopy densities – the switch from surface/flood irrigation methods to pressurized drip and microsprinkler orchards as well as

March 26, 2020

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

June 30, 2019

WUE Part 2: Kernel Yield per Inch of Water

Water use efficiency (WUE) within agriculture has became a bit of a buzz word over the past few years. This is mostly due to the heightened awareness of the public due to the drought. This has placed a lot of emphasis on water usage within agriculture, in which many are demanding that water should be used at the highest efficiency. Almonds are no exception to this. WUE is essentially how much crop we can produce with a given amount of water. This is not an easy value to determine due to the complexity of many farming systems. Once determined, however, it provides an insight into determining issues affecting productivity. Within almonds, there have been attempts to determine optimal WUE. Monitoring of yields in several orchards over the last 10 years has determined a theoretical WUE of 83 lbs of crop for every inch of water use (essentially 1000 kernel lbs of crop for every acre foot of water use). Previous work within a production almond orchard from a single site in California found it to be around 70-72 lbs per acre inch of water use. This range was supported by research work in Australia. Interestingly, anecdotal evidence from water cuts experienced during the drought suggests a similar range, with many farmers experiencing yield losses around 800-1000 lbs/acre for every acre foot of water reductions. To further explore this concept and expand the findings across may locations, three trials were established across California. These trials are located in Kern, Merced, and Tehama Counties and are studying the effects of varying water use amounts on yield. Results from a previous year have been written about earlier. As shown in table 1, our results from the Merced County trial found an average of 73 kernel lbs per acre inch of water use. This

October 5, 2016

2016 Mid-Spring Update

The crop is developing nicely in many areas across the areas of the San Joaquin Valley in which I observed. Crop loads vary, depending on last season’s stress or crop-load, but generally look good. Looking forward to this week, there area few pointers to keep in mind. Rain is forecasted for this weekend with chances through next week. This will have minimal impacts on the physiological development of the crop. It will, however, impact the amount rates of evapotranspiration and soil moisture. This variance should be accounted for by either using soil moisture monitors or plant based measurements. If possible, rain gauges (or other measurement tool) should be placed at the various farms as rainfalls can be variable. Last year, for example, a thunder cell dropped around 3/4″ of rain in a farmer’s field on the North side of Livingston, while his block on the south side received less than 1/4.” Accounting for these differences can prevent the “stalling-out” of growth from over-irrigation. Even though it warmed up this week, it might be wise to question the start of the irrigation season. Only two out of four plots in which we are measuring stem water potential have indicated the need to irrigate. The other two are still reading around baseline…one is even in a Delhi sand. Plant based measurements should be used to help determine the need to irrigate. Remember: the tree is essentially a giant tensiometer with a lot larger volume of soil impacting the result. Disease update: Multiple days of rain are predicted. This could mean conditions suitable for Bacterial Spot (especially on ‘Fritz’ and ‘Padre’), Anthracnose (for ‘Monterey’), Scab, and Shot-hole. Lingering infections of green fruit rot may also progress. If a treatment is warranted, check the fungicide efficacy table. Remember to rotate away from the last spray

April 8, 2016

Planning for your summer tree nut weed control

Written by: Kurt Hembree, UCCE Farm Advisor, Fresno County Winter weeds were abundant this year, thanks to the high amount of rainfall we had. Hopefully you found time between storms and were able to get into your orchards and treat for weeds. Given moist soil conditions and warming temperatures close at hand, summer weed growth is also expected to be high. So, are you ready to go with your summer weed control program? Hopefully you already know what weeds you’ll be up against. If not, look to see if there are new ones emerging in recently-watered orchards or after the last rainfall. Note specific weeds so herbicide(s) can be selected accordingly. When it comes to herbicide selection, make sure you’re using products that are effective against your specific weeds, which often vary from field to field. Also, select herbicides and rates that are appropriate for the soil type; lower rates of preemergent products are often needed on sandier soils than heavier soils. Consider using sequential treatments where appropriate if rainfall occurs in April, which can help extend control through summer. Remember to add postemergent products to the tank if weeds are already up and growing when you treat. If glyphosate-resistant horseweed, hairy fleabane, junglerice, or ryegrass are present, and you still want to use Roundup or a similar material, be sure to add another burn-down material that is effective on those weeds. Combining Treevix or Rely 280, Lifeline, or similar product with Roundup has worked well on these and a wide variety of weeds. Be sure to treat when the weeds are small for optimum control. Don’t wait to spray when weeds are large, droughty, or dense, or herbicide coverage and performance may suffer. Use spray tips, a spray volume, and spray pressure that adequately wets the weeds, while minimizes

April 1, 2016

Bloom Bt for Peach Twig Borer Control

Written by John Edstrom, UCCE Farm Advisor Colusa County, Emeritus Hopefully, the central valley will finally receive drought relief from recent El Niño driven storms. The resulting wet soil conditions, however, can prevent orchard access for many orchard operations including dormant sprays. Without dormant insecticide sprays, peach twig borer (PTB) populations can increase dramatically and threaten next years crop. Worm reject levels were troublesome and costly to many almond growers this past season and point to the need to control PTB. Besides kernel damage, twig borer feeding also kills young buds and shoot tips after bloom and deforms young tree scaffold limb development . Fortunately, growers have a very safe alternative to dormant sprays using Bacillus thuringiensis (or Bt) to control PTB during the bloom season without harmful side effects to applicators or the environment. Other insecticidal materials claim to be safe to bees but may negatively impact bee colony health. Bt has no adverse affects to any stage of honeybees or the health of the hive.  Bt is a natural bacterial based insecticide that is toxic only when ingested by lepidopteran larval stage pests and is completely safe to beneficial predators and parasitoids. Bt is exempt from pesticide use regulations and so is particularly useful near urban or environmentally sensitive areas. The bloom Bt control strategy has proven effective since its was developed in the 1990s during a time when regulations were restricting the use of the highly toxic organophosphate spray materials. Bt is a perfect fit for almond IPM programs. Its only down side is that multiple applications are needed for complete control. Fortunately, Bt products are inexpensive and can be tank mixed with fungicides applied for blossom and leaf diseases around bloom, so the total costs are comparable or less than standard insecticides. Generally, two sprays are

January 18, 2016

2015 Top Ten Articles

In maintaining the tradition of counting down the end of the year, below are the top ten articles read in 2015 from the readers of “The Almond Doctor.” 10: It’s the Nut Price, Dummy. A great article by Franz Niederholzer that discusses the rationale behind the increased plantings. It was the number one read article in 2013, number 3 in 2014. 9: Leaffooted Bug Advisory for Almonds: Two of our IPM advisors, Kris Tollerup and David Haviland, provided an advisory for Leaffooted Plant Bug after the mild conditions of the 2014-2015 winter reduced insect mortality. 8: Almond Bloom 2015: General considerations for various concerns at bloom. An annual topic during a time of year with highly variable conditions. 7: Understanding and Applying Information from a Soil Test, Part 2: A part of a series of articles discussing soil nutrients as determined through a soil analysis written by Allan Fulton. 6: Proper Almond Tree Planting: An excellent article written by Brent Holtz discussing proper tree planting methods. Considering the number of new plantings in 2015, the article finding its way into the top 10 isn’t too surprising. 5: Drought Management for Almond: Drought was a major challenge for many operations in 2015. This article discusses strategies to help reduce the impacts of water stress and drought. 4: The Seasonal Patterns of Almond Development: Back from the dead, this 2009 article picked up over 1700 reads which may be due to the increase of almonds in the media. It covers the general biology of the tree and stages through the year. 3: More Leaves than Flowers: Why? : This past year, in many orchards, flower density was lower than normal, and trees pushed more leaves earlier than in the season. Issues from 2014 had a carry-over effect into 2015, and this article explains a few

December 31, 2015

Considerations for a Potential Wet Year

The prolonged drought has increased the media buzz of the predicted El Nino. Although weather data suggests that it may be a strong pattern, it still doesnt mean automatic relief for the California water situation. In saying this, however, there stands a good chance that we will receive average rainfall, which means that things may be wetter through the winter months. Winter sanitation, planting, and orchard maintenance are easier when it is dry. Operations can move quickly since the days are nice and orchards are accessible. If it rains frequently, however, these operations may be hindered. So whats the back-up plan? Orchard sanitation. Weather assists with the various practices of orchard sanitation. Storms help remove leaves and mummies from the tree. Furthermore, rain helps degrade mummies once they are on the ground, reducing over-wintering populations. Trees are also easier to pole, which may have to be an option if heavy shaker equipment cannot be used for concerns of compacting wet soil. If possible, once harvest operations are completed, it may be best to begin winter shaking once a few rain events have occurred. Even if this doesnt remove every mummy, it will make it easier on poling crews. Planting and replanting new blocks. Wet winters can be highly problematic for planting new orchards. Soil preparation is difficult in wet conditions as too much equipment work will compact the soil, creating future issues with infiltration and tree growth. Fields need to be ripped, backhoed, or slip-plowed in dry soil, prior to rain events. Rain that falls after the modification is performed will help with settling. Post-modification leveling and disking should occur after some rain, but before the fields are too wet. Prior to planting, land may need to be disked again due to settling, and berms should be pulled as soon

October 1, 2015

Soil Moisture Sensors

Soil moisture sensors are great tools to aid in irrigation management. They provide feedback on the movement and depth of moisture within the soil, providing the ability to identify the proper duration of irrigation. Proper use relies on a thorough understanding of the soil characteristics of the orchard, which include soil type, water holding capacity, and salinity level. Sensors can be used to help schedule irrigation. Timing of irrigation usually occurs when moisture levels drop below certain trigger points at varying depths. These points are different for every soil and sensor type and require in-field calibration to help reduce unwanted plant stress. Calibration can occur by comparing sensors readings to plant stress responses (e.g. Pressure chamber readings) or to a “feel” test to determine how much water is still available to the plant. Several factors need to be considered when planning to install the sensors. Sensor locations should be placed to account for varying soil types of the orchard. If only a few locations are planned, the predominant soil types should be selected. If possible, sensors should be installed at varying depths to provide moisture levels in the middle, bottom edge, and below the active rootzone. A common 3 sensor installation pattern is 12-18″, 30-42″, and 48-60.” Work by the University of California has compared many soil moisture monitoring systems. Neutron probe data, dielectric, tensiometers, and electrical resistance blocks have all been found to respond to water applications similarly. Essentially, if sensors are properly installed and maintained, and time is taken to understand and interpret the data, they can provide similar information. The table below highlights some of the varying aspects of these systems. Each system has strengths and weaknesses. Please note that the sensors types are linked and when clicked will direct to further information. “Feel” Tensiometers Dielectric Sensors

July 10, 2015

Using the Pressure Chamber to Schedule Irrigation in Almonds

Written by Matt Jones, Staff Research Associate, UCCE Merced County Determining the appropriate time to irrigate is among the most critical tasks facing growers and farm managers. Traditionally, growers have relied on orchard water budgets using ET and CIMIS stations, and monitoring soil moisture levels to develop irrigation schedules. For in-depth explanations of these methods, consult the UC ANR Almond Production Manual. However, these methods only indirectly measure water status of trees in an orchard. To directly and quantitatively measure tree water status requires the use of a pressure chamber. One of the quantities a pressure chamber can measure is stem water potential (SWP), or the amount of tension in the water column as it is pulled from the soil and through the plant. For a complete guide on pressure chamber use and plant-water relations, see UC ANR Publication# 8503. But what do these numbers mean, and how can they be used in irrigation management? Interpreting these numbers depends on temperature, relative humidity, and the degree and type of water stress you are trying to manage with an irrigation set. Knowing temperature and relative humidity will establish what normal or ‘baseline’ pressure chamber values (in bars) would be for an orchard that is fully irrigated. Baseline values can be  precisely determined by looking at table 14 in ANR Pub 8503. However, a rough estimate baseline (in almond) is to divide temperature by ten. For example, if it is 100 F, then your baseline value is -10 bars. The values measured in the field and how they deviate from baseline will determine the degree of tree water stress, and irrigation timing. If aiming for a fully irrigated, mature orchard, then irrigate when the measured SWP values are 4 bars lower (more negative) than the baseline. For example, if the baseline value

July 1, 2015