David Doll0 commentsJanuary 10, 2016Horticulture

Can mechanically-applied pollen either supplement bees, or ensure an almond crop in the event of bee inefficacy or unavailability?

Written by Elizabeth J. Fichtner, Farm Advisor, UCCE Tulare County and Katherine Wilson, Staff Research Associate, UCCE Tulare County Each year during almond bloom, a fraction of growers try artificial pollination as either a supplement to bee pollination or an insurance policy against bee-inefficacy.  Several factors may impact the availability and efficacy of bees as pollinators for California’s (CA) almond crop. Increasing almond acreage has increased the overall demand for hives while chronic honey bee health issues limit hive supply.  Additionally, bee efficacy for pollination may be challenged by adverse weather conditions during bloom.  In an effort to either supplement bee pollination or provide an insurance policy against inefficient bee-pollination, growers have utilized two different approaches to artificial pollination:  1) mechanical application of pollen to trees by blowers or airplanes, and 2) insertion of pollen dispensers (‘inserts’) into hives. Conceptually, the application of pollen to trees by blowers relies on bee activity to redistribute pollen within the orchard; only a small amount of the blown pollen would be deposited directly on receptive stigmas. Several research studies, however, have demonstrated that techniques involving “blowing” pollen onto trees have no benefit as a supplement to bee pollination on fruit set or yield (ie. Schupp, 1997). A published 1966 almond research trial similarly demonstrates a lack of benefit of supplemental, mechanically-blown pollen on Nonpareil nut set and yield in a 2:1 block of Nonpareil and Mission (Thorp et al., 1967).  Conversely, a study in 1978 demonstrated a value of mechanically-blown pollen on nut set (Thorp, 1978), but replication of the study in 1979 did not demonstrate any effect of artificial pollination (Thorp, et al. 1979). The orchard housing the 1978 and 1979 trials was chosen due to its unfavorable varietal combination (1:4:1, with 4 contiguous rows of Nonpareil) –a combination not utilized by

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Brent Holtz0 commentsNovember 30, 2015Horticulture

Pruning First Leaf Potted Trees

Written by Brent Holtz (UCCE San Joaquin) and David Doll (UCCE Merced) The first dormant pruning of potted trees can present some difficulties when selecting primary scaffolds. Potted trees are often planted throughout the year because growers are no longer limited to planting bare root trees while they are dormant. Many successful orchards have been planted throughout the year, including in the months of July and August. These potted trees often have produced branches that have unsuitable angles, placement, or girth to develop into primary scaffolds. With this in mind, it is best to treat unpruned potted trees that are two to eight months of age as if they were recently planted bare root dormant planted trees and prune off all of their branches in the first dormant season. By doing so these trees will push new growth the following spring that should have enough branches from which to choose primary scaffolds that are spaced properly around the tree with appropriate vertical angles (~45 degrees). October – April planted trees may have to be treated differently. In this case, it may be best to not prune these trees and allow them to push the new growth. After 2-3 months of growth – or after trees have extended the new growth 12-18 inches, the trees should be pruned back similar to that of a bare root in January. This will create better branching angles while not reducing the vigor of the tree. Cutting too much off of too young of trees may stunt the tree’s growth. It may also be better to not sucker these trees until adequate girth is achieved.

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Brent Holtz2 CommentsNovember 14, 2015Horticulture, Soil

Whole Orchard Soil Re-incorporation: an Alternative Orchard Removal Strategy

Written by Brent Holtz (UCCE San Joaquin) and David Doll (UCCE Merced) You may have heard the news—co-generation plants are limiting the amount of chipped biomass they are accepting.  This is reducing the rate in which old orchards are removed, impacting the orchard redevelopment process. The soil incorporation of chipped or ground almond, peach, plum, or cherry trees during orchard removal could provide an alternative to co-generation plant or burning and could add valuable organic matter to our San Joaquin Valley soils.  Traditionally, many growers feared that wood chips or grindings would stunt tree growth by either allelopathic compounds or reduced nitrogen availability due to the high carbon to nitrogen ratio.  Interestingly enough, recent research has found this not to be true if the ground material is spread across and incorporated into the soil In 2008, University of California Farm Advisors and a USDA Plant Pathologist undertook a project at the UC Kearney Research and Extension center to compare the grinding of whole trees with burning as a means of orchard removal.  Twenty-two rows of an experimental orchard on nemaguard rootstock were used in a randomized blocked experiment with two main treatments, whole tree grinding and incorporation into the soil with ‘The Iron Wolf,’ a 50-ton rototiller, versus tree pushing and burning.  We examined second-generation orchard growth and hypothesized that soils amended with woody debris will sequester carbon at a higher rate, have higher levels of soil organic matter, increased soil fertility, and increased water retention.  Second generation almond trees (Nonpareil, Carmel, Butte) were planted in January/February 2009. The whole tree grinding did not stunt replanted tree growth.  In 2015, Greater yields were ultimately observed in the grind treatment, when compared to the burn (previous year’s yields were similar). In 2013, 2014, and 2015, soil analysis revealed  significantly more calcium,

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David Doll8 CommentsOctober 25, 2015General, Horticulture

Planning and Planting a New Almond Orchard

When planning a new orchard, it is important to consider location, water availability and quality, irrigation system selection, pre-plant soil modification, rootstock, and variety selection. Mistakes made during the planning process will be present throughout the orchard’s life. Below are some considerations to keep in mind when selecting a site, rootstock, and variety. Site selection and modification. Soil type. Soils that have a high water holding content can be problematic when trying to access the orchard in early spring. Furthermore, these soils may also increase the risk of “wet feet” and Phytophthora infections. Rocky soils can make  orchard operations like harvesting and mowing challenging, but generally can be managed unless it is more rocks than soil.  Saline-alkaline soils will have challenges with water infiltration. These soils often require pre-plant leaching or modification to leach salts. Salinity. Soil salinity should be below1.5 dS/m as an average of the rooting depth (five feet). To determine the salt levels, soil samples should be collected from each of the differing soil types in the field.. Sample plugs or auger cores of each soil type in 4-5 locations. At each location, sample every 12 in of depth to 60 in. Combine and pool samples at a given depth (e.g. combine and mix 4-5 samples at 12 in depth, 4-5 samples at 24 in depth etc).   A composite sample should be pulled for every 20 acres, with a minimum of three samples for smaller fields. Nematodes. When soil sampling for salinity and soil nutrients, set aside some of the soil  from the 12-24”   depth samples for nematode analysis. Submit the soil to a lab that can test for nematodes. For almond and other stonefruit, nematodes of concern are ring, root lesion, and rootknot. If counts are greater than 50 per liter (or 500 grams) of soil

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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 commentsSeptember 15, 2015Horticulture

Planting Potted Plants: Preventing Root Girdling

It is the time of the year when many operations plant potted almond trees. Although potted trees are convenient with the year round availability and planting time (almost any month if properly irrigated),  there are a few considerations at planting that must be considered in order to prevent root girdling and future orchard loss. Root girdling of trees occurs when roots grow in odd directions. These roots wrap over or around other roots or the trunk, eventually preventing the flow of water and nutrients while limiting structural integrity. The problem is usually not noticeable at first, but 6-8 months after planting, the trees begin to show reduced growth. Later, these trees often become victim of wet feet or Phytophthora due to over-irrigation of the tree. Over-irrigation occurs from to the inability to pull water at the same rate due to the constricted xylem and reduced canopy size in comparison to healthy trees. In cases in which the trees survive and are kept through the third leaf, they may snap off at ground level from the shaking process. The issue seems to be more severe with more vigorous rootstocks. Root girdling is often caused by root kinks. Root kinks occur due to the misdirected growth of roots as they become pot-bound. It is not uncommon to see tree roots growing up or around when left in a pot too long. Some modern pot technology may help reduce the occurrence, but any tree, if kept to long, would have excessive root kinks. Root girdling can be prevented by planting trees that do not have observed root kinks. Trees should be examined prior to planting. If the trees have lignified roots (woody roots) which are growing in multiple directions, it is important to return the plants or break the root ball up in attempts

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David Doll0 commentsApril 17, 2015Horticulture, Insects

Early Nut Split – Nut Drop or Bug Damage?

A few samples and farm calls have yielded nuts that are splitting pre-maturely. These nuts tend to be yellow in color and are often found dropping from the tree during high winds. Sometimes, the nuts have gum along the suture, or gum “specks” on the outside of the hull. These nuts could either be a “June Drop” as the tree is balancing the crop load or it could be kernel death caused by leaf-footed plant bug. The nuts dropped  could be the last dropping period within almonds. These nuts, when cut open, would be brown at the base of the nut, indicating the death of the connective tissue. Gum may exude from the suture of the hull. More importantly, there would be no noticeable holes through the hull or in the shell, although some degradation of the shell cells may occur. In contrast, Leaf-footed plant bug would have a pin hole through the hull. This hole would often extend through the shell and into the kernel, causing a darkened spot at the point of entry and a shriveling of the kernel. Gum may appear on the exterior of the hull where the bug entered its mouth parts, but does not always occur. Although gumming is usually immediate (if it occurs), nut yellowing and subsequent drop — based on research — occurs 14-23 days after the point of feeding/damage, variety dependent. Gumming is not as frequent on younger nuts. Knowing the cause of drop can provide information relevant to treatment decisions. If the drop is due to leaf footed plant bug, a treatment may be warranted. It is important, however, to determine if the bugs are still within the orchards. Since the nut drop is visible several weeks post feeding, the bugs may have moved out of the orchard and the

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David Doll6 CommentsFebruary 17, 2015Horticulture, Irrigation

More Leaves than Flowers: Why?

I have received a few reports about poor bloom conditions on ‘Nonpareil.’ In these cases, flower density appears to be low and leaves are starting to push (See Figure 1) indicating that the fruit buds did not develop over the past year. From the reports, trees tend to be between the ages of 6 and 12 years old and have been observed across Merced County. A number of issues may be responsible, including the following: Water stress. Reductions in water resources over the past year have led to reduce vegetative growth in many orchards. This lack of growth prevents the formation of vegetative buds (in-season) which develop into fruit bud (post-harvest through dormant period). Research has shown that spurs that remain in good light positions tend to “take a year off” after bearing fruit, while others receiving too much shade die. Therefore, canopy growth must be maintained to some extent to keep crop loads high. Salinity Induced Water Stress. Increasing soil salinity decreases the osmotic potential of the soil, making the plant “work harder” for water. This leads to water stress and reduces the energy diverted into vegetative growth and floral bud development. High yields over the past few years. Trees producing large yields in successive years have been observed to have an “off year.” This is due to most of the plants energy being diverted into the crop load, reducing the amount available for developing new fruiting spur positions. As discussed earlier, if this happens in successive years, the number of viable fruit spurs may be reduced leading to a reduced crop. Re-leafing in the Fall after leaf drop from foliar disease, salt, or mites. Bloom density would be lower if the tree defoliated last summer or fall from lack of water, too high of salt levels, foliar disease,

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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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Katherine Pope7 CommentsJanuary 13, 2015Horticulture

Counting Chill Better – Using the Chill Portions Model

Part 2 of 3 in the series – What can we learn from the low chill winter of 2013-2014 In my last post, Is Last Year’s Warm Winter the New Normal?, I discussed low chill winters like last year’s coming more often in the near future. The first step to preparing for those warmer winters is counting chill better – moving from counting in chill hours to counting in chill portions. What makes the chill portions model (also called the Dynamic Model) better? There are three basic difference between the chill hours model and the chill portions model. Chill hours counts any hour between 32°-45° F as the same. Chill portions gives different chill values to different temperatures. No more wondering about the value of ‘warm’ chill hours. Temperatures between 43°-47° F have the most chill value. The chill value on either side of that range are lower, dropping to no value at 32° F and 54° F. Chill hours only counts up to 45° F. Chill portions count up to 54° F. This makes chill portions better able to approximate how the trees we grow, most of which evolved in fairly mild climates, count chill. Chill hours does not subtract for warm hours. Chill portions can. The math is tricky, but the concept is simple: Chill portion accumulation is a two-step process. First, a ‘chill intermediate’ is accumulated, but can be subtracted from if cold hours are followed by warm hours. Second, once the chill intermediate accumulates to the certain threshold, it is converted into a ‘chill portion’ and the chill intermediate count starts over from zero. The chill portion cannot be undone by later warm temperatures.

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