David Doll2 CommentsJuly 20, 2009Nutrient

Potassium thiosulfate toxicity on almond

During periods of high heat and the corresponding high evapo-transpiration, several unique orchard problems can occur. Most of these are due to fertigation methods which have been widely adopted to increase fertilizer application efficiency. The benefits of fertigation greatly outweigh most negative impacts, but caution must be used as a simple mis-calculation can cause orchard damage. A field call from a grower in late June demonstrated the potential problems that can occur with fertigation. Observations of yellowing leaves, leaf drop, and death of lower limbs raised concerns by the grower and pest control advisor (PCA), prompting an orchard visit. Initial Observations: Upon arriving to the 11th leaf Sonorra/Nonpareil/Carmel (all on Nemaguard) orchard I noticed excessive leaf drop across all varieties (Picture 1). Most of these leaves were coming from the interior of the canopy, suggesting the possibility of drought stress from improper irrigation scheduling. Lower leaves found on the interior of the canopy were burnt back, with a crispy texture. Leaves closest to the trunk that were completely yellow were beginning to abscise, while leaves on the tips of the branches remained green (Picture 2). This is in contrast to lower limb dieback, which causes soft yellow leaves found on the ends of interior branches. Picture 1: Leaf drop associated with the over-application of potassium thiosulfate. Picture 2: Leaf wilting and “dieback” associated with the over-application of potassium thiosulfate. Note how the interior branches are more affected than the branches on the outside edge of the canopy. Up-Close Observations: Close inspection of the leaves revealed a necrotic tip, or burnt region of the leaf. This leaf was surrounded by a yellow halo (Picture 3). Typically, a yellow halo around a necrotic area would suggest the possibility of almond leaf scorch, but due to the widespread occurrence of the problem, this

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David Doll7 CommentsJuly 13, 2009Nutrient

Mid-July Leaf Sampling for Almonds

Leaf analysis of almond is a useful tool in diagnosing deficiencies, toxicities, and future nutrient needs of the tree. It provides an up to date analysis of the mineral composition of the tree, with desirable concentration of different elements known through extensive University of California research. Reasoning for sampling. As almond trees increase in size, their demand for nutrients also increases. Tree nutrient concentration is dependent upon the growth rate of the crop and the amount of nutrients that have been supplied naturally or through fertilizer. Under certain conditions, plant tissue may become deficient which could limit further growth and crop quality. Depending upon the nutrient and level of deficiency, remediation is possible in the current season, dormant period, or early spring of the following year. Leaf concentrations of major elements (nitrogen, phosphorous, and potassium) can be used along with kernel yield per acre to determine the nutrient budget for the next season. Process of sampling. Sampling should be distributed in a regular pattern across the block, with fully expanded leaves pulled from non-fruiting spurs on branches at least 6 feet high. About 100 leaves are needed for each sample. Leaves should be picked from trees of the same variety, age, rootstock, and soil type. Trees samples should be at least 100 feet apart and 20 trees are needed to ensure accuracy and confidence with the results. Partitioning of larger sampling blocks is advised to determine tree size and yield variability. Label the samples so the sampling location is known, and keep cool until they are sent to an analytical lab. Interpreting the results. Leaf analysis results are recorded either in percentages (%) or parts per million (PPM) of each element in a given weight of dried leaves. The table below contains the critical values for almond leaves sampled in

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Brent Holtz10 CommentsJune 30, 2009Diseases

Hull Split Part 2: Hull Rot of Almond

As almond trees approach harvest, at about mid hull split, clusters of dry leaves begin to appear scattered through the tree canopy. Individual spurs, small shoots or entire small branches may collapse due to hull rot infections (Photo 1). The loss of fruiting wood, especially in the lower parts of the tree, can negatively affect yield for years to come. Nonpareil is usually the most severely affected cultivar though Sonora and Kapareil can also sustain extensive damage. Hull rot is caused by either of two fungi, Monilinia fructicola or Rhizopus stolonifer. Monilinia fructicola is best known as one of the brown rot fungi and R. stolonifer is often called the bread mold fungus, and will turn bread left out black and moldy. Photograph 1: Hullrot of almond caused by Rhizopus stolonifer. In the southern San Joaquin Valley I believe that Rhizopus is the primary pathogen responsible for hull rot while Monilinia may be more important in the Sacramento Valley. These two organisms are very different but can cause similar disease symptoms on almond. As the name implies, a lesion or dryish rotted area develops on the hull, and dense masses of Rhizopus spores produce a powdery dark gray to black growth between the hull and the shell (Photo 2). Monilinia spores are buff-colored and can be seen on inner and outer hull surfaces. The nut meat is not damaged, but a toxin produced in the infected hull moves from the hull into the neighboring leaves and shoots causing death of these tissues. Neither Monilinia nor Rhizopus are able to invade the healthy outer hull surface. Only after hull split begins can spores gain access to the inside of the hull and initiate infections. Once hull split starts, trees are at risk of becoming infected. One or both pathogens may be

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David Doll1 CommentJune 27, 2009Insects

Hull Split is Approaching…

Hull split is approaching the the central San Joaquin Valley. In Kern COunty, hullsplit of almonds has been observed on the edges of blocks and tops of the trees, and will progress rapidly from this point forward. Hullsplit is a traditional time of making an application of insecticide to reduce navel orange worm damage and late season mite pressures. Blanks, or unpollinated or aborted fruit, will split first before the rest of the crop. So, as a grower, what do we need to keep in mind during hull split? 1. Insect pest management, which includes Navel Orange Worm and Spider Mites. 2. Water Management to reduce the incidence of hull rot. We will cover point 1 today, and the disease hull rot later this week. 1. Insect Pest Management practices for Hull split. Spider Mites: A miticide will be necessary if a pyrethroid was used within the orchard. Pyrethroids target both spider mites and predator mite populations. Once the predator mites are reduced, the faster reproducing problematic spider mites can flare up, causing tree defoliation. It is essential to include a miticide tank mixed if spraying a pyrethroid. If not using a pyrethroid, scouting the trees can give you an idea if you need to include a miticide. Scouting for mites is simple, should be done in the morning when it is cool, and can give a good idea about the ratio of predator mites to spider mites in your orchard. Please refer to the University of California Integrated Pest Management page for information on how to scout for mites: UC IPM Scouting for Spider Mites. There are several miticides to choose from at hull split. The most commonly used include Acramite, Envidor, Fujimite, Kanemite, Oil, Omite and Zeal. Each of these products can be effective, depending upon populations of

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David Doll16 CommentsJune 22, 2009Horticulture

The Seasonal Patterns of Almond Production

When reviewing previous posts of this blog, I realized that not much information has been provided about the general biology of the almond tree. To cover this area, I decided to focus on the seasonal cycle of almond trees. In general, the season progresses in the following pattern: Dormant,Delayed Dormant, Bloom, Post-Bloom, Fruit Development, Harvest, and Post Harvest. Each period will be broken down and discussed. Dormant:As the temperatures from the late fall continue to drop, the tree enters a period of rest that lasts through December/Early January. At this time, the tree has dropped all of its leaves naturally or through an application of zinc, and is maintaining a low level of water use and starch consumption. This “low” flow of starch through the tree is needed as the catabolic breakdown of starch to sugar prevents the sap from freezing. This is, of course, only if the tree was able to develop enough starch reserves in the previous fall. In the rare occasion of low starch reserves, cold damage can occur leading to canopy and scaffold loss. Picture 1: A dormant spur. The cold temperatures that the tree is exposed to at this time helps with the development of the fruit buds. The tree requires a certain amount of moisture and chilling hours to come out of dormancy. Once the chilling hour requirement has been met, bud grown will begin with warmer temperatures. Chill hours are dependent upon the variety,but almonds generally need between 500 and 600 chill hours. In general, chill hours are the number of hours between the temperatures of 32-45 degrees Fahrenheit. Winter hours above 60 degrees are subtracted from the totals. Delayed Dormant:In late January/early February the tree begins to push a flush of fine feeder roots. These roots provide moisture and nutrients for the

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David Doll8 CommentsJune 16, 2009Diseases

Foamy Canker in Almond

This is one of the most visually moving diseases found in almond. Once upon the location of the problem, not only is the disease obvious by looking at the trees, but the air is also filled with a fermented-like smell reminding one a bar when entering for happy hour. Overall Orchard Information: The orchard I was called out to visit was described as a complete loss to foamy canker. To me this came as a bit of a surprise as foamy canker typically comes later in the season. By time I have arrived, the grower was in the process of removing the orchard. The entire orchard was exhibiting symptoms of foamy canker (Picture 1), poor growth and dieing trees. Photo 1: Overview of the almond variety Fritz with foamy canker The orchard was a Nonpareil-Fritz-Monterrey on Lovell planted on clay/clay loam soil. The trees were in their 4th Leaf trees with average growth. Nut set of the trees was decent, but not great. Speaking with the grower, he mentioned that the orchard has a high water table, found at about 7 feet with subbing up to 4-5 feet. Quality of the water was unknown. The site is also high in boron within its soil, and has a history of verticillium wilt (old tomato and melon ground). Overall, the discussion yielded that there were many issues from the start with the orchard – over 30% of the Fritz variety planted in the first year did not survive and needed to be replanted. Irrigation of the trees tends to be minimal due to the high water table. The grower does not irrigate often – only 8 inches last year through double line drip. Nitrogen usage is minimum, but tree vigor is high due to being the first generation orchard on old row

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David Doll1 CommentJune 9, 2009Weeds

Herbicide drift damage to a Butte/Padre almond orchard by 2,4-D

May is the time of the year for the herbicide injury to almonds. High winds, fast growing weeds, and too many orchard tasks to complete in a day are the typical causes of herbicide drift. Herbicide drift can be prevented by following a few simple principles:1). Avoid windy days when applying herbicides,2). Apply the correct herbicide that targets the correct weed,3). and apply the herbicide at the proper rate. A field call in mid-May by a grower yielded a case of typical 2,4-D injury to almond. The 2nd leaf orchard was 50% Butte and 50% Padre on nemaguard rootstock. The orchard was situated in sandy soil with microsprinklers used for irrigation. The grower reported multiple trees showing dieback of new growth. He was uncertain of the cause and thought verticillium wilt may be affecting his orchard. Picture 1 shows the overall symptoms of an affected almond tree. Picture 1: Overall tree symptoms caused by 2,4-D herbicide drift. Note tip dieback and odd growth. Overall, the distribution of the symptoms were found throughout a large percentage of the block. Many trees where showing a “shepherd’s crook” of the new growth indicating either a wilt disease or herbicide/salt issue. Picture 2 shows the severity of the symptoms on the new growth of the almond tree. Picture 2: Branch tip dieback due to 2,4-D herbicide drift. Leaves at the tip of the crook were crispy, indicating a fast wilt. Shoots with contorted growth were found throughout the canopy. Pictures 3 and 4 are of these symptoms. Picture 3: Branch damage from 2,4-D herbicide drift. Branch is showing the “shepherd’s crook” symptom, typical of vascular wilt pathogens or salt/chemical damage. Picture 4: Contorted growth of new growth caused by exposure to 2,4-D herbicide. With the exception of the contorted growth, symtpoms expressed by the

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David Doll1 CommentJune 4, 2009Nutrient

Zinc Deficiency in Almond

A farm call in early April yielded a problem that proved to be difficult to diagnose due to complicating factors. The orchard was three years old with three varieties planted on nemaguard rootstock: 50% Nonpareil, and two pollinators Monterrey (25%) and Avalon (25%). The soil was loamy sand to sand, very coarse, and a hardpan was present. Tree sites were backhoed before planting to remove the hardpan within the tree site. The previous cropping cycle was almond, but methyl bromide was used to fumigate the soil to kill nematodes, soil pathogens, and weeds. Irrigation is by moveable sprinklers. Initial Observations:Overall the orchard has variable growth overall. Some trees are large, some trees are smaller. Branches in the top of the tree have sparse growth. This growth, however, seems to be limited to one variety – the nonpareil. The symptoms are therefore found in every other row. Photo 1 shows the symptoms of sparse growth in the upper trees of one row. Photo 1: Overview of the orchard showing symptoms. Note that the symptoms are more severe on one row of trees. Up-Close Observations:Sparse tree growth has tufts f leaves that are “bootstrapped.” Leaves are deformed are have not completely formed physiologically. Photos 2 shows a symptomatic tree and photo 3 shows a close up of effected leaves. Photo 2: An individual tree showing symptoms of poor leaf growth and development. Photo 3: An isolated branch showing “bootstrapped” leaves. Possible causes:Glyphosate (Herbicide) damage (Round-up)Dormant applications of chloropyrifos (insecticide) (Lorsban)Zinc Deficiency Diagnosing:The applications of chloropyrifos, a broad spectrum insecticide, can sometimes lead to similar growth responses in almond when applied in the delayed dormant stage. Questioning of the grower yielded that no chloropyrifos was used within the orchard – in fact, he doesn’t use chloropyrifos in any of his orchards. Good –

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David Doll0 commentsJune 4, 2009Diseases

Ceratocystis of Almond

Ceratocystis or “mallet wound canker” has been found on almond throughout California for almost 50 years. This fungal canker, caused by Ceratocystis fimbriata, can develop on areas of the trunk or branches that have been damaged by tractors, hedgers, and harvesting equipment. Pruning wounds are also susceptible. Cultivars that are most susceptible include Nonpareil, Mission, and Ne Plus Ultra. Ceratocystis cankers appear as either water soaked or dry cankers. Amber-colored gum is found at the canker margins. Infected tissue turns brown and the area eventually becomes sunken. Unlike Phytophthora infections, Ceratocystis remains active during the summer months in which rapid canker growth can occur. Cankers can girdle limbs, scaffolds, and tree trunks.Limbs 4-6 inches in diameter have been observed to be girdled in 3-4 years, while smaller branches are killed more quickly. Ceratocystis cankers appear as either water soaked or dry cankers. Amber-colored gum is found at the canker margins. Infected tissue turns brown and the area eventually becomes sunken. Unlike Phytophthora infections, Ceratocystis remains active during the summer months in which rapid canker growth can occur. Cankers can girdle limbs, scaffolds, and tree trunks.Limbs 4-6 inches in diameter have been observed to be girdled in 3-4 years, while smaller branches are killed more quickly. Several species of sap-feeding beetles and fruit flies spread Ceratocystis. These insects feed on the fungus, ingesting and coming into bodily contact with the spores. The spores are then transported to other trees and deposited on the bark by the insects. Rains and sprinkler irrigations can wash the spores into fresh pruning wounds or other injuries. Once the fungus infects the cambium, it will begin to invade the healthy bark and xylem tissues of the tree. Dark stains may permeate into the heartwood of the tree, but rarely is the fungus found in these tissues.

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