Brent Holtz0 commentsNovember 5, 2017Diseases

Aspergillus niger induced hull rot on almond

Written By Brent Holtz, Ph.D., UCCE Farm Advisor San Joaquin County   In September I visited an almond orchard in San Joaquin County with the Supareil variety showing symptoms that looked very similar to hull rot typically observed on Nonpareil.  Symptoms showed dieback of vigorous young shoots and lower limbs (photo 1-blighted shoots).    Leaves were stuck on many shoots and typically blighted while hulls were unusually shriveled (photo 2-shriveled hulls), with fungal sporulation observed on the inner hull next to the shell (photo 3-fungal sporulation).  The fungal sporulation, however, didn’t look similar to the sporulation typically observed on hulls infected with Rhizopus stolonifer or Monilina fructicola, the typical pathogens associated with hull rot of almond.  Many of the larger blighted shoots seemed to still be alive even though they had defoliated, while other blighted shoots were starting to push new leaves in September—not typical of blighted shoots infected with Rhizopus or Monilinia. Samples of infected hulls were sent to Dr. Themis Michailides, a plant pathologist with UC Davis / Kearney Research and Extension Center, where he isolated Aspergillus niger from 88% of the samples collected.  The other 12% of the diseased nuts collected were found to be infected with Rhizopus stolonifer, the typical bread mold pathogen commonly associated with hull rot.  Aspergillus niger has not commonly been associated with hull rot in the San Joaquin Valley, but Dr. Mohammad Yaghmour, Farm Advisor in Kern County, has also observed similar hull rot. Hull rot can reduce yields of vigorous young almond orchards in the central and southern San Joaquin Valley.  Symptoms often observed are dieback in lower limbs that often exhibit less bloom in the spring.  I’m wondering how the Supareil return bloom will be in this particular orchard next spring?  I believe severe hull rot can enhance the shading out

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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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Brent Holtz0 commentsJanuary 27, 2014Weeds

Dormant Weed Control in Tree Nut Crops 2014

by Mick Canevari, Brent Holtz, and Brad Hanson Current dry weather has preempted most normal winter weed germination and growth while prolonged periods of dry soil has caused some early weeds to desiccate and die.  In most tree and vine herbicide trials conducted so far this winter–the untreated controls look similar to herbicide treatments, very clean and without weeds.  What to do at this point poses some interesting questions.  Will it rain? Most of us are worrying more about irrigating our almond trees this summer than controlling weeds right now. If you have some weed growth that germinated with rain our one December rain, or with fall and winter irrigations, you may want to apply a post-emergent herbicide now in order to prevent hard to kill weeds from becoming established.  The warm weather could allow these weeds to establish and become more difficult to control, impacting the success of later herbicide applications by increasing trash on the berm and reducing coverage. 

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Brent Holtz2 CommentsJanuary 9, 2013Weeds

Dormant Weed Control in Tree Nut Crops 2012-2013

 Written by Mick Canevari and Brent Holtz, UCCE San Joaquin. Weeds have a tremendous capacity to spread within an orchard.  The first line of defense is  identifying the weeds you need to control, and selecting the best herbicides or cultural practices to control those weeds.  If you use the same herbicide(s) each year, a shift to tolerant weed species will ultimately take over and a loss of herbicide effectiveness will occur.  Alternating products with different modes of action at least every couple years will improve results and insure herbicides long term viability.  The UCIPM web site has charts that show which weeds are controlled by what herbicides, and an excellent weed photo gallery that includes many weed species commonly found in California for easy identification and reference http://www.ipm.ucdavis.edu/.      

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Brent Holtz5 CommentsJune 22, 2012Diseases

Perennial Canker of Almond

Written by Brent Holtz, UCCE San Joaquin County Symptoms of perennial canker of almond. Photo by F. Niederholzer. Perennial Phytophthora Canker has killed many almond trees. Two plant pathogenic fungi, Phytophthora cactorum and Phytophthora citricola are primarily responsible. This disease is lethal, perennial, and is not associated with pruning wounds which differentiates it from “Pruning Wound Canker.” Perennial Phytophthora Canker kills almond trees by girdling the scion and is usually initiated in a conducive environment either below the soil surface or on the tree trunk where the trunk and branches join. Phytophthora cactorum is usually associated with infections initiated near the soil surface, while Phytophthora citricola typically causes aboveground infections initiated near tree branch crotch pockets. Dr. Greg Browne, USDA-ARS, has found that the source of inoculum for above ground infections is likely debris from the orchard floor containing fungal spores that are blown onto trees during harvest. This debris and spores are most likely washed off the tree during rains, with some accumulating in main-branch crotch pockets or depressions where main branch scaffolds join the tree trunk. These scaffold pockets containing soil, water, and fungal spores most likely offer a conducive environment for Phytophthora infections to take place. Dr. Browne’s research has provided almond growers with some control measures that can be taken to prevent Perennial Phytophthora Canker. He has shown that phosphonates (e.g. inorganic and organic salts of phosphonic acid) have provided systemic activity against a number of diseases caused by many of the Phytophthora species of plant parasitic fungi. The phosphonic acid derived from phosphonates probably disrupts Phytophthora growth and appears to intensify almond tree defenses against infection. Fortunately, the phosphonate can be translocated both upwards and downwards in the tree due to its mobility in both xylem (water going up) and phloem (sugars going down) tissues.

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Brent Holtz9 CommentsJanuary 17, 2012Horticulture

Plant New Trees High!

Written by Brent Holtz, UCCE San Joaquin CountyOne of the worst things that can happen to young trees from nurseries is that they are planted to deep. Sometimes  they are initially planted at the right height, but then a berm is thrown up around the trees and their crown (the graft union between the scion and rootstock) is covered with the soil from the berm. I saw many diseased trees last spring that had Phytophthora root and crown infections and every one of them had their graft union below the soil line; sometimes the union was more than six inches below. If you are planting or replanting, trees should be planted high on small mounds as shallowly as possible. Planting depth after settling should be no deeper than in the nursery, and the graft union should always be well above the soil line. Try to follow some of these planting tips: 1. Dig a hole deep enough so the roots are spread out and not cramped, 2. Plant the trees so that the nursery soil line is above the current soil line, 3. Plant the highest root a little above the soil line and then cover it with extra dirt, and 4. When planting allow for 3-6 inches of settling in the planting hole. I have never seen trees die from being planted too high, but I have seen many trees killed by being planted too low. This is especially true in heavy soils with a high clay content. These soils have slow water percolation, drain slowly, and remain saturated longer than well drained sandy soils. The mound around the tree trunk forces excess water to drain away from the tree, thus reducing the length of time the crown is exposed to excess surface moisture. Saturated soil conditions can occur

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Brent Holtz5 CommentsDecember 27, 2010Horticulture

Proper Almond Tree Planting

When planting a new orchard, precautions should be taken to prevent tree loss. Care should be taken to reduce direct damage to the trees. Trees should be planted as soon as possible once received from the nursery. Always cover bare roots with a tarp when transporting trees on back of a trailer, making sure to keep the roots moist. If the trees are heeled in, fumigated soil or sawdust should be used and excess moisture should be avoided. Cold storage should be avoided if possible. If cold storage is necessary, then trees should be fully dormant and the roots kept moist. Care should be taken to ensure that trees are properly planted. In heavy soils, planting on berms is recommended to help drain water away from the crown of the tree. Berms should be pulled before planting to ensure that the graft union is above the soil. Do not pull a berm after planting as this may cover the graft union. Planting depth after settling should be no deeper than in the nursery and the graft union should always be well above the soil line. Holes should be dug deep enough to accept the root system; no deeper. If a crust or soil glaze occurs, break up or slice to ensure proper root growth. Planting trees high will help reduce losses to the root disease Phytophthora. The only exception is trees grafted to Marianna 2624 plum rootstock; they should be planted at the same depth they were at the nursery to avoid suckering from the roots. When planting, try to follow some of these tips: 1. Dig a hole deep enough so the roots are spread out and not cramped, 2. plant the trees so that the nursery soil line is above the current soil line, 3. plant the highest

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Brent Holtz12 CommentsMarch 15, 2010Nutrient

Fertilizing one-year old trees – be careful!

Nitrogen is the most important element we can apply to our tree fruit crops. Almond growth and productivity depend on the availability and uptake of nitrogen. Most fertilizer recommendations are based on making nitrogen available to our trees so that a nitrogen shortage does not limit tree growth or productivity. Young almond trees don’t require as much nitrogen as older trees. I like Wilbur Reil’s rule of “one ounce of actual nitrogen per year of age of tree”. That rate can be applied several times per season, but never more than that at any one application. Thus, a first leaf (first year in your orchard) almond tree should not receive more than one ounce of actual nitrogen per any application. A five year old almond tree should not receive more than 5 ounces of actual nitrogen per one single application. The University of California only recommends one ounce of actual nitrogen per one year old tree over the course of the season, but I have been told by many growers and PCAs that this rate is not enough for the growth they desire. So, if you want to put out five ounces of actual nitrogen per one year old tree, do so in five applications and not all at once! I have seen many trees burned by nitrogen, especially if liquid fertilizers like UN-32 (urea ammonium nitrate 32 %) or CAN 17 (a clear solution of calcium nitrate and ammonium nitrate) are used in single applications. These liquid fertilizers are very effective and easy to use but it doesn’t take much to burn young trees. I do not suggest using these liquid fertilizers on first leaf trees–I prefer to see triple 15-15-15 (15% Nitrogen – 15% Phosphorous – 15 % Potassium) fertilizers used on first leaf trees. I like to

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Brent Holtz0 commentsFebruary 2, 2010Diseases

Bloom sprays: What and when to use to provide effective disease control.

Written by Brent Holtz, UCCE San Joaquin Almond trees are susceptible to bloom and foliar diseases when it rains at bloom, and the decision of when to spray and what fungicides to use can be quite difficult. In the San Joaquin Valley we are usually in a low precipitation region and we cannot predict when and how much it is going to rain. We often receive rain during bloom which can result in favorable conditions for several plant pathogenic fungi to cause spring time diseases of almonds. The main diseases in almonds are Brown Rot Blossom Blight, Green Fruit Rot or Jacket Rot, and Shothole. Other less familiar diseases include Scab, Rust, Leaf Blight and Anthracnose. The fungi that cause these diseases are usually always present in almond orchards, sometimes in higher or lower amounts depending on the previous year’s disease levels and current environmental conditions. Fungicide Control ProgramsGenerally, a good disease control program is based upon a wise choice of fungicides and good timing and coverage. Growers should assess the diseases present in their orchards and select materials carefully. Not all fungicides are equally effective on all diseases (fig. 1). It is a good idea to use more than one kind of fungicide for a broader spectrum of activity. This will be especially important with using Strobilurin fungicides (Abound, Cabrio, Flint, Sovran, and Pristine). Pristine is a Strobilurin fungicide that is combined with Carboxyanilide to slow resistance development. Resistance to these fungicides can develop over time and repeated use, thus try to rotate the fungicides you use. Two successive applications of the same mode of action should be avoided. Information on effective fungicide rotations can be found in figure 2. A suggested bloom spray strategy:Usually two sprays are made for brown rot control. The first is usually done at

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