David Doll4 CommentsOctober 17, 2017Irrigation, Nutrient

Almond Kernel Defects

It has been a challenging year in regards to kernel quality within almonds. Several issues have emerged including insects, diseases, and deficiencies. Samples of each of these have been brought to the office for identification. In doing so, I thought it would a good idea to share what we have found with the accompanying figure. Each of these problems seem to have a set of circumstances that led to an increased observance of the problem in 2017. They include: Leaf-footed plant bug. These large bugs damage the kernel by feeding. There was a larger over-wintering population in 2017 which is thought to be due to the milder winter and increased vegetation that occurred from the increased rain. Damage was reported on nearly all varieties, but was particularly bad on ‘Aldrich’ and ‘Fritz.’ If the feeding occurs early in the season it will kill the kernel. Later feeding occurring as the shell hardens and the embryo matures will not kill the nut but cause staining and sometimes gumming. The defining characteristic is a sunken black spot located on the kernel. Boron deficiency. This deficiency can occur in areas with clean surface water and low soil boron and is observed regularly on the east side of the central valley. Boron deficiency can lead to gum that crystallizes on the end of the kernel and is not in response to a feeding wound. A hull analysis should be conducted to determine boron levels as leaf levels are not indicative of tree boron status. A hull analysis under 80 ppm indicates deficiency and boron should be applied to the soil to bring the trees to sufficient levels. Insect damage. Navel orangeworm (NOW) was high this year with reports as high as 40% in late harvesting varieties. Lack of winter sanitation due to the rains

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David Doll0 commentsSeptember 19, 2017Nutrient

Almond Postharvest Management: Nitrogen Considerations

Written by David Doll (UCCE Merced) and Franz Niederholzer (UCCE Yuba-Sutter-Colusa) Applications of nitrogen in the postharvest period have been promoted as a good farming practice.* Trees utilize nitrogen at this time to rebuild nitrogen stores and provide nutrients for bud development. Research from the Kern County nitrogen trials found that trees can absorb approximately 15% of annual nitrogen demand in the 8 weeks after harvest (30-45 lbs/acre, excluding application inefficiencies). This work was done in a highly productive orchard (3000+ lbs/acre) and applications were applied as multiple fertigation events through the entire year. Fertilizer nitrogen applications should be made as soon as possible after harvest to allow the trees the most time to absorb fertilizer nitrogen before the leaves drop, when root nutrient uptake essentially stops. Whole almond tree nitrogen need after harvest is much less than in the spring (no shoot growth or crop), therefore fall fertilizer nitrogen needs are relatively minor compared with leaf out to hull split.  Fall nitrogen fertilization need is further reduced by remobilization of leaf nitrogen into woody tissue storage as trees prepare to drop their leaves in November (if they are not burned off with zinc sulfate.) Interestingly, recent research suggests that late postharvest fertilization (October) can be skipped if mid-July leaf nitrogen levels are adequate (over 2.5% nitrogen). This work by Franz Niederholzer conducted at the Nickels Soil Lab in Colusa County has found no negative impact on yields when skipping postharvest nitrogen applications within orchards over the past two years. In this trial, trees had mid-July leaf nitrogen values of 2.55% or greater. Trees receive 0 or 30 lbs/acre of postharvest nitrogen in mid October. Trees didn’t receive late zinc sulfate foliar spray and maintained leaves up to or through Thanksgiving. Over the past two years, there were no differences

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David Doll0 commentsSeptember 9, 2017Horticulture, Irrigation

Almond Postharvest Management: Water Demands

After the hustle of harvest, it is easy to think that the orchard work is nearly wrapped up for the year. With almonds, this isn’t the case. Research over the past 30 years has identified the postharvest period as the primary development period that impacts next year’s crop. Not surprisingly, much of this work has shown proper irrigation practices during this period being the major factor. For this article, the post-harvest period will be defined as mid-August through early November. During this period, the trees can demand an estimated 12-15″ of water based on location and weather. Roughly 70% this demand is from the six weeks immediately after harvest – when the days are hot and longer (see included table). Shorting trees of water during this period of high water use (mid-August through September) has been shown to significantly reduce next year’s yield. In fact, research by David Goldhamer and Elias Fereras have found that the first 8″ of water applied during the postharvest period is the MOST CRITICAL water applied to maintain orchard yields. Why is this?  Almond floral bud differentiation, unlike other Prunus spp.,  begins in mid- to late-August and continues through early September. Water shortages during this time reduces carbohydrate development, leading to less energy being able to be directed towards the creation of next year’s flowers, affecting both flower quality and quantity. This, in-turn, leads to an overall reduction in fruit load. Practices should be employed to keep leaves on the tree through the postharvest period (early November).  Reducing tree stress through the harvesting process is the first step in maintaining highly productive trees. This includes being timely with shaking so trees are stressed for a minimal amount of time and understanding the amount of soil moisture and the rate of use – which includes taking

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David Doll3 CommentsJune 23, 2017Horticulture

What influences hull-split timing?

Hull-split often occurs around the end of June though the first week of July within the San Joaquin Valley. The start and duration of hull-split is influenced by the variety, weather, and tree stress. As many are aware, the variety has the strongest influence on hull split initiation and progression, but this article will focus on the influence of weather and tree stress. Most people believe the weather experienced in mid-June strongly influences the start of hull-split. Research has indicated, however, that this is not true. Work by Ted DeJong (UC Davis Plant Sciences), has found that the beginning of hull-split (which is indicated as 1% hull split) can be predicted by weather conditions experienced during the first 90 days after bloom. Cooler conditions experienced during this time will lead to a later hull-split, while warmer conditions result in an earlier split. Temperatures in the latter half of the spring and early summer have a minimal influence on nut progression, regardless of being warmer or cooler than normal. The model can be found at http://fruitsandnuts.ucdavis.edu/Weather_Services/almond_hullsplit_prediction/ and can be applied using localized CIMIS data. There is some evidence to support that tree stress and nutrient status influences the duration of hull-split. Stress in June decreases water content within the hulls, which means a faster drying time when they begin to split (think of hull-split progression like a bell-shape curve – stress in June shortens the x axis).  This is often related to high heat experienced in June, which leads to tree stress due to inability to properly manage the irrigation or the application of regulated deficit irrigation (RDI). Nitrogen status of the tree also influences the rate of split, in which trees having a higher nitrogen content have a longer duration of hull split. Often vigorous orchards are grown with minimal

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David Doll3 CommentsMay 30, 2017General, Technology

Small Drones and Monitoring Orchards: Project Update and Field Day

Aerial imaging can provide real-time information to growers regarding water usage and crop health. Within agriculture, these tools provide a valuable service for identifying problematic areas within fields, thereby increasing efficiencies for both small and large scale producers. Currently, most aerial imaging is conducted by flights with mid-elevation aircraft or satellites. These flights and corresponding images are usually conducted by a service company and provided on a weekly or monthly basis. Autonomous or Unmanned Aerial Vehicles (UAVs) may provide a format in which more regular flight data can be obtained. Most discussions within agricultural settings have been focused around large fixed wing drones. However, smaller, less sophisticated and less autonomous UAVs could provide a useful platform for California farmers. These smaller UAVs would be less expensive to construct, may require less regulatory permitting, and provide a mobile platform that can be quickly deployed within a field setting. In these settings, small UAVs would have the ability to quickly monitor crops for water stress, nutrient management, and pest and disease epidemics. A major barrier for small UAVs is camera/imager selection and processing. Currently, most work within crop stress management has focused on the use of thermal cameras that operate in the far-infrared spectrum (Maes and Steppe, 2012). These cameras are expensive, which inhibits the adoption of UAV technology. More commonly used spectral wavelengths, such as visible and near-infrared wavelengths can be used for other vegetation indices need to be researched to determine if they provide comparable results as thermal imaging. These imagers and indices are attractive to the end-user due to the lower cost to implement. With these challenges in mind, a research project sponsored by the University of California Agricultural and Natural Resource Competitive Grants Program was awarded to determine the feasibility of using small UAVs for perennial crop water

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David Doll0 commentsMay 24, 2017Other Crops

Walnut Pruning Trial – Update and Field Day

A study evaluating central leader training, minimal pruning of walnuts in comparison to traditionally trained walnuts has been ongoing within Merced County for the past six years. Over this period, the unheaded, minimally pruned ‘Chandler’ trees have cumulatively out-yielded the headed, or traditionally pruned, walnuts by an estimated 1500 lbs/acre over the first four harvests (p<0.05). The greatest yield difference between the two treatments occurred during the first harvest (3rd leaf) in which the unheaded walnuts outproduced the headed walnuts by 750 lbs/acre (p<0.05). Since that time, the trees have had relatively similar crop loads with no observed differences in limb breakage between treatments. Leaving trees unheaded after the first growing season provides the opportunity for the walnut tree to develop lateral fruiting positions during the 2nd growing season. These positions set with crop the next year. Headed trees, in contrast, respond to the 6 foot heading cut made following the first dormant season after planting with vegetative growth, reducing the energy directed toward developing lateral positions. The differences in response as well as the reduced canopy associated with pruning are believed to explain the differences in yield. Observations made within the local field trial have provided some considerations if this technique is planned to be adapted.  In-season limbs should be removed to develop the central leader in the dormant period after the first year of growth. Trees should not be painted during dormant period between the first and second year as it may suppress bud growth in the lower positions. Selected limb thinning should occur to allow orchard equipment access. Work in other varieties is ongoing, and should be done more experimentally within an operations as there does seem to be some differences among varieties. ‘Chandler,’ however, is performing consistently with this method across the state. Observations of the

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David Doll4 CommentsMay 13, 2017Diseases, Horticulture

Almonds Exuding Clear Gum

Several calls about gummy nuts were received this week. Of concern are nuts that are oozing clear gum along the suture or side of the hull. There are many potential causes of clear gumming, which include bug damage, boron deficiency, and internal causes from an expanding kernel. Bug damage. Most people are aware of leaf footed plant bug damage. Feeding by this insect can kill the almond embryo when the insect inserts its needle-like feeding tube into the nut. This often leaves a small pin-prick hole which results in clear gum being exuded 3-10 days after feeding. Although the risk of the bug killing the embryo decreases after shell hardening, there can be some staining of the kernel. As the season progresses, feeding by plant bugs decrease, while stink bug feeding can increase. These insects do not have long enough mouth parts to feed on the kernel, but feed on the fruit instead. They often have several feeding points on a single nut. All of these may gum. Severe feeding by stink bugs may impact kernel quality, but the economic threshold of these insects is unknown. Boron deficiency. Too little boron can cause gumming. Usually a clear gum exudes out of the side of the nut or suture line. When cutting the nut open, the kernel is often discolored with copious amounts of gum. These nuts often drop from the tree, and if not, the gum can harden and misshape the kernels, impacting kernel quality at harvest. Another sign of deficiency is a low crop set. Tree boron status should be determined by hull analysis – which has been discussed previously.  This type of deficiency is common in areas that use clean surface water and have not applied any boron to the soil. Physiological- expanding kernels. Occasionally, almonds can gum for no apparent reason.

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David Doll0 commentsApril 17, 2017Diseases

Alternaria leaf spot of almond

The late rains we are receiving will increase the risk of Alternaria. This pathogen (Alternaria alternata) requires warm temperatures and leaf wetness to infect almond trees. A few weeks after infection, small circular lesions form, eventually increasing to the diameter of 1/2-3/4.” Occasionally, there is a yellow halo. Older lesions often develop a black ring of spores. Typically, the leaves are infected in mid- to -late April or May, with the symptoms occurring several weeks later. The disease develops rapidly in the summer, especially when there are heavy dews. The varieties ‘Carmel,’ ‘Sonora,’ ‘Monterey,’ ‘Winters,’ and ‘Butte’ are more susceptible than other varieties. This problem tends to be more frequent and severe in the south San Joaquin Valley and the western side of the Sacramento valley. In wet years, severe problems occur throughout California. Alternaria can be managed by utilizing cultural practices and fungicide sprays. Orchards with high humidity, heavy dew, and stagnate air often have severe problems. Selected pruning of the canopy can help increase ventilation. Improving water infiltration can reduce orchard humidity. When designing an orchard, rows should be oriented in parallel to prevailing winds to assist with ventilation. Other practices that assist in reducing leaf wetness and canopy humidity should be considered. Fungicides should be considered if the orchard or area has a history of the disease. Orchards should be scouted for signs of the disease in April through June. If Alternaria is found, treatments should begin – usually about mid-April. In orchards with a history of the disease, treat in mid- to late April and 2 to 3 weeks later. FRAC groups 3, 7, 11, and 19 used alone or in combination are effective in preventing disease. If making multiple sprays, fungicides should be rotated to prevent the formation of resistance. More information on fungicide selection can be found here.

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David Doll3 CommentsApril 10, 2017Irrigation

Yellow Trees from Being Too Wet

It is very common to see yellow trees in the spring. The lack of color is often due to saturated soils which reduces the movement of oxygen into the soil, killing fine feeder roots. This impacts the ability for the tree to take in water and nutrients, leading to micro-nutrient deficiencies, impacting nut set and tree growth. In severe cases, especially with younger trees, the symptoms are similar to glyphosate drift or zinc deficiency. Later-season carry-over effects are also observed and include a limited rootzone, which leads to severe water stress during hull-split and harvest. Most of the time, this problem is caused by the orchard being irrigated too soon. Many operations apply water because it is perceived as needed or they are wanting to apply fertilizer. The need to apply water, however, is usually very low in the spring due to the cooler conditions and crop stage. Based on the 30-year average almond evapotranspirational values across California, water use from Mid-February (bloom) through the first week of April for almonds across the State ranges from 3.6″ to about 4.25.” This demand is often met by rain and the tree accessing stored moisture within the soil. To determine when to start applying water, plant stress or soil moisture levels should be monitored. The soil profile should be starting to dry at the two to three feet zone and can be checked with with the use of a shovel, auger, or soil moisture sensors. If using the pressure chamber to monitor plant stress, irrigation should be considered when trees are 1.5-2 bars more negative than baseline. For more information on the use of a pressure chamber in perennial crops, please see this document. If wanting to apply nitrogen, applications should occur by ground application or the shortest fertigation set as possible. These practices will help to properly time the first

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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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