David Doll2 CommentsSeptember 26, 2021Horticulture

Reduced Kernel Size – 2021 Harvest

There have been several reports of smaller than expected nut size for the 2021 harvest. Nonpareil sizes have been reported to be in the range of 28-30/ounce rather than the typical 24/25 nuts per ounce. Many have suggested that this is due to drought induced water shortages, but this has occurred even on fully irrigated orchards. Water stress has played a role, but earlier conditions of the season should also be considered. Nut weight is influenced by a few different factors. These include: Reduced number of cells; Reduced cell size; Reduced cell weight. Cell number is mostly impacted by temperatures that occur during cell division, which occurs early in the season, typically within 6-8 weeks following fertilization. Cell enlargement is influenced by plant stress. It begins in April and continues through May. Lastly, weight accumulation begins in May and continues until early August. It is influenced by plant stress, which reduces the production of carbohydrates. To maximize nut size, carbohydrates (sugars) must be available during these periods for cell building processes. Carbohydrate availability is influenced by the rates of photosynthesis and respiration. These two processes are heavily influenced by plant temperature, which are influenced by ambient air temperature and water availability. Temperature influences photosynthesis and respiration. Both processes increase rapidly as temperatures warm, and begin to drop as temperatures increase above a certain point. The peaks, however, are different, with 86F and 103F for photosynthesis and respiration, respectively (figure 1). Since these peaks are different, there is a net gain of carbohydrates when temperatures are below 86F, but a net loss as temperatures increase above this point. Furthermore, as temperatures warm towards 86F, there is more energy being directed towards respiration, which reduces availability to be used for other processes, like nut development and plant growth. Internal plant temperature is

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David Doll7 CommentsMarch 17, 2017Diseases

Bacterial Canker and Blast

Over the past few weeks, there have been a high frequency of problems reported with bacterial canker and blast. Bacterial blast results in blighted blossoms and causes crop loss. Interestingly, when there is a high frequency of blast, the very similar disease of bacterial canker appears a few weeks later in young trees(we are starting to get reports of canker now). Both of these problems are complicated. They involve the bacterium Pseudomonas syringae, plant stress which is often mediated by nematodes, and the weather. P. syringae is an interesting bacteria. It lives naturally on plant surfaces as an epiphyte – meaning that it generally does not cause problems. During wet winters which create a favorable environment, bacterial populations increase and spread through the tree and orchard. At some point the population becomes large enough that it begins to invade plant tissues – starting with buds (bud drop), then flowers (blast), and finally bud scars and other openings which leads to bacterial canker. Tree health has a lot to do with the susceptibility to P. syringae infection. Generally, if the tree is healthy, infections rarely occur. Weak, young trees- usually three years or less- are susceptible to bacterial canker which can cause the loss of tree scaffolds or death. Mature orchards usually don’t exhibit bacterial canker symptoms, but rather have blast and bud drop problems. Orchards with severe problems are typically planted in sandy soils, which often tend to be acidic, hold less water and nutrients as well as being more conducive to plant parasitic nematodes. All of these factors, if managed improperly, can increase tree stress, increasing susceptibility. Some micronutrient deficiencies, notably iron, have been found to increase susceptibility, while balanced, proper major nutrient fertilization has been shown to reduce occurrence.  Severe water stress can also increase occurrence, and is thought to be due

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David Doll9 CommentsFebruary 23, 2017Horticulture

Freezing Temperatures:Almond Frost Sensitivity

There is a frost risk for the next few nights with temperatures dropping into the high 20’s and maybe lower. If these forecasts are true, crop loss could be experienced within colder areas of almond orchards. As written previously, there are some tasks that can be performed to help reduce the risk of frost damage. These include mowing the cover crop or residual vegetation to allow radiant heat form the soil to move into the canopy, use of sprinkler systems to apply water which warms the orchard, or utilization of equipment or fans to help move warmer air into the orchard. All of this is to help increase orchard temperatures by 2-3 degrees. The risk of frost increases as almonds break dormancy and begin development. Dormant buds are relatively tolerant to freezing conditions, but sensitivity increases as flowers develop from pink bud to full bloom, then into nutlets. The following figure selected from “The Almond Production Manual,” developed by Joe Connell and Richard Snyder, demonstrates the change in sensitivity. Essentially, sensitivity does vary slightly by variety, but a 50% or greater of crop loss can be experienced during bloom when temperatures drop to 27F for 30 minutes. After petal fall, this temperature threshold increases to 28F. Colder temperatures can cause significant crop loss. Implementation of frost protection measures should be considered when temperatures approach freezing as orchards are often colder than forecasted temperatures. Mowing must be done prior to the frost event. Irrigation systems applying water during the night will provide a heating effect even with a wet soil surface due to heat being released off the water as it freezes. In essence, with these systems, more water equals more protection. Targeted amounts of water should be 30-40 gallons per minute per acre. Minimally, water should be applied at rates higher than 15 gallons/minute/acre to

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David Doll0 commentsJanuary 12, 2017General, Horticulture, Weeds

Dormant Practices and Wet Weather

Over the past week, a lot of rain has fallen across California. Orchard access should be limited during periods of wet soil to reduce soil compaction as well as stuck equipment. Limiting access, however, creates challenges in performing a variety of orchard operations, including the list below.   Winter Sanitation. Removal of almond mummies from trees is critical for Navel Orangeworm management (NOW). Many operations usually wait for the first rains to help with leaf drop and to help “loosen” the mummies. In wet years, however, it becomes difficult to winter shake the trees as orchard conditions remain too wet for access of shakers. Furthermore, the “window” to winter shake is limited on the late end as fruit bud loss increases as trees enter delayed dormancy and buds swell (Mid to late January, depending on location). To manage this limited access, operations should consider poling crews. If these aren’t available, and sanitation is not performed, a spring timed (usually late April through early May) insecticide can reduce overwintering NOW. This strategy is not as effective as winter sanitation, but is better than doing nothing. Insecticide sprays targeting NOW in the dormant period are NOT effective due to NOW pupae being inside of the almond mummies. Planting bare root trees. Hand planting crews have an easier time than machine planting due to limited field access. If planting delays occur, trees should be placed into cold storage at the nursery as soon as possible to reduce the risk of leaf out and weakened trees. Keep trees in cold storage until ready to plant. Unless there is no other option, do not take delivery of trees in bins or plant them in a temporary location at the farm. On delivery, check tree roots to make sure they are healthy and living (should be

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Franz Niederholzer2 CommentsJanuary 25, 2016Horticulture

Wet or Dry, Get Ready for Bloom

Franz Niederholzer, UCCE Farm Advisor, Colusa/Sutter/Yuba Counties Spring isn’t here yet, but it will be before we know it. What happens then, weather-wise, and how you react to those conditions could change the season for your operation. But, no one can be certain of the weather this spring. Will it be wet? The forecasters think there is a good chance for that. If that’s the case, more bees and bloom sprays, and less irrigation will be needed. But, they could be wrong and 2016 could be another dry year. Better plan for a wet or a dry spring. Here are some things to consider: Topic Wet Dry Bees Higher hive stocking rates (3 hives per acre, minimum of 6-8 frames, with one frame of brood) are recommended in wet years. Spray carefully. No difference from the last few years. Make sure bees have water sources and fungicides are applied with bee health in mind. Click HERE1 for link to Almond Board BMPs for bees. Bloom sprays With rain at bloom, UC recommends 2 bloom sprays – pink (5% bloom) and full bloom. If it is warm at bloom, use material(s) with anthracnose activity. If it continues to rain, more fungicides will be needed. The more fungicides used, the greater the need to rotate chemistries. Click HERE2 to see info on fungicide efficacy/timing/resistance management. One bloom spray, timed before or at full bloom will provide good disease control under dry (no rain) bloom conditions. Weed management Properly selected and applied preemergent herbicides, sprayed before rain saturates orchard soils, provides weed control when you can’t get into too-wet orchards. Pre or post emergent sprays will control weeds. Don’t fall behind. Controlling weeds saves water. Nitrogen management 20% of annual N budget should go on by mid-March. If it’s still raining after petal

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David Doll4 CommentsOctober 1, 2015Horticulture

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

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David Doll0 commentsMay 8, 2015General

2015 Mid-Spring Updates

A lot of excitement this past week with the passing storms. Some large thunderstorms passed through Merced Co. dropping some hail and rain. As with any thunderstorms, rainfall totals vary. A few calls have yielded some concerns which are highlighted below. 1. Irrigation for areas with low rainfall totals will most likely still be needed. Use is highly variable depending on the weather, but for the most part, a warm (>80F) sunny day will require 0.25″ of water/acre to maintain full irrigation for a mature block. Cloud cover and cooler temperatures can reduce demand by as much as 1/2. This is using an assumed Kc value of 1.00. 2. Ants. Fields should be scouted and, if needed, baits should be applied. Baits – since they are growth regulators- must be applied 1 month prior to harvest for maximum effectiveness.  Be mindful that not all ants present within the orchard feed on almonds. A quick trick to distinguish “good ants” from “bad ants” is to throw potato chips or a hot dog near the mound. If consumed, it can be assumed that the colony will also feed on almond kernels. Another trick is to  stomp near the mound to bring ants to the surface. If they swarm out of the mound, are red in color with a black butt and bite, they are mostly likely fire ants. Monitoring and treatment information can be found on this previous post and at the UC IPM Website . Ants often cause more damage than expected. High populations can consume between 1-2% of the crop within four days. 3. Hail damage. Hail can cause crop loss as it knocks nuts and new growth form the trees. Nuts that are “bruised” may fall 3-5 days after the damage occurred. If the nut remains on the tree, it will typically yield

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Katherine Pope8 CommentsJanuary 22, 2015Horticulture

Chilling Requirements in Chill Portions for California Crops

Part 3 in the series – What can we learn from the low chill winter of 2013-2014 In my last post, Counting Chill Better – Using the Chill Portions Model, I discussed how the chill portions model (also known as the Dynamic Model) is different from the chill hours model. Now that you can figure out how much chill you got in chill portions, how much do you need? Below is a table of the estimated chilling requirements of most of California’s major tree crops, and a few particular important cultivars. Most of the requirements listed below are based on scientific research. A few (*) are estimates based on how much chill we got last winter and how the crops responded in the spring and at harvest. If you are interested in the requirements of cultivars not listed here (especially for apricots, cherries, peaches and nectarines) or want to know the scientific reference information for a particular estimate, check out the more thorough version of this list at the UC Davis Fruit & Nut Center site.

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David Doll4 CommentsDecember 15, 2014Diseases

Recent Storms and Tree Loss

The high wind from this past weeks storm has caused damage to orchards throughout the State. Trees have been blown over, uprooted from the strong winds, which will impact crop yields and orchard stand. This damage usually can be categorized into two categories – trees that have blown over from a failed root system or from heart rot disease. Failed Root Systems. Damage to almond trees from failed root systems tends to occur in younger orchards and is characterized by leaning trees within saturated soils. 

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