David Doll4 CommentsSeptember 21, 2009Horticulture

Post Harvest Pruning of Mature Orchards

Pruning is one of the subjects that can have ten people explain it in ten different ways. This has to do a lot with the traditional thoughts on how an almond tree should look, the believed benefits of pruning, and personal experiences. It is one of the most important practices of orchard maintenance due to the expense and its effect on orchard yield and longevity. Therefore pruning should be considered more of a science than an art. Pruning can be broken down into two phases: The tree training phase and the maintenance period phase. During the tree training phase, we work to establish and shape the permanent framework of the tree through primary and secondary scaffold selection. This occurs through the first three years of the orchard life. The maintenance pruning phase occurs from the 4th leaf on and is done to maintain the shape of the tree. This post will focus on pruning during the maintenance period of the orchard life. In order to understand the principles of pruning, we need to understand the underlying principle of orchard management: We are farming sunlight. The more sunlight that is intercepted by tree leaves, the more production we can achieve within our orchard. Therefore, trees need to fill the available space as quickly as possible to achieve maximum yields. Along with this, we want to ensure orchard viability by having sufficient fruitwood to produce a sizable crop for the life of the orchard. So, to do this, do we need to prune? The short answer is “no.” Studies by by farm advisors Roger Duncan (Stanislaus Co.), John Edstrom (Colusa Co.), Bill Krueger (Glenn Co.), and Mario Viveros (Emeritus, Kern Co.) have demonstrated that pruning does not increase yield over minimally, or “unpruned” trees (Table 1). As we can see, conventional, annually

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David Doll0 commentsSeptember 14, 2009Horticulture

Inspecting the Orchard During the Post-Harvest Period for Damage

Shaking has almost been completed throughout many almond orchards. Through this process, a lot of stress has been placed on orchard trees. Trees may have also been damaged throughout the duration of the growing season or during the harvesting process. After harvest is completed, it is helpful to walk the orchard and observe for problematic areas. Things to look for:Shaker or other mechanical damage that may lead to infection by Ceratocystis,Mite damage or webbing in trees,Areas containing a large amount of stick-tights,Excessive leaf defoliation due to either mite infestation or lack of water,Gumming of the trunks or scaffolds,Areas affected by hull-rot,and/or areas of poor nut pick-up. To find out how to prevent this problems, look for patterns. Does the damage appear in any specific locations, such as at the end of irrigation runs, near irrigation valves, areas of different soil textures, or near orchard borders? Were shaker damaged trees shook at the beginning or end of the day? Is only one variety affected? Identifying these patterns will provide valuable clues about what went wrong and allow corrective practices for the coming year.

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David Doll3 CommentsSeptember 8, 2009Insects

Taking a harvest sample for orchard IPM check-up

The collection and crack-out of a harvest sample is often forgotten during the bustle of the harvest. It is, however, one of the most important practices to employ as it provides a “progress report” of your season’s IPM program. A sampling of 500 nuts from orchard blocks that underwent differing pest management practices should be collected after shaking but before sweeping. These nuts can be stored in a refrigerator for 2-3 weeks until time is available to shell the kernels and inspect for insect damage. This sample will indicate what pests are in the orchard to help determine the management activities for the next year. Furthermore, it will serve as a record to compare with the huller/processor grade sheet. Insects that cause economic damage to almond kernels include navel orange worm (NOW) (Picture 1-2), ants (Picture 3), oriental fruit moth (OFM) (Picture 4), and peach twig borer (PTB) (Picture 5), and leaffooted plant bug (Picture 6). NOW actively chews and bores through kernels, often leaving behind webbing and excessive white frass. Ants feed on the kernel skin and can hollow out kernels, leaving behind piles of “sawdust” like frass. The OFM and PTB cause similar damage on almonds, causing shallow grooves on the kernel. The only difference is that OFM leaves behind small amounts of reddish brown frass. Damage by the leafooted pant bug is noted by dark spots on the kernels. Picture 1: Navel Orange Worm Damage to a mature almond. Picture 2: Webbing and excessive frass left by navel orange worms. Picture 3: “Sawdust-like” frass left by ants. Picture 4: Damage by Oriental Fruit Moth. Note the reddish frass left behind. Picture 5: Peach Twig Borer damage found on almond kernels. Note the lack of frass and shallow grooves. Picture 6: Darkened spots caused by the leaf-footed plant

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David Doll6 CommentsSeptember 1, 2009Horticulture, Nutrient

Postharvest Care for Almonds

We are mid way through almond harvest. As we finish up shaking our Nonpareils, we need to keep in mind the list of orchard tasks to help maintain crop production for the next year. For almonds, flower bud differentiation takes place during the month of September. This means that next year’s bloom and subsequent crop is being formed in the middle of this year’s harvest. During this time period, there are three important cultural practices that need to be considered by almond growers.They include irrigation, nitrogen fertilization and pruning. 1. Post-harvest irrigation is very important to keep the leaves active and functioning until normal leaf drop, which typically takes place at the end of October, early November. By preventing premature defoliation, we let the tree transition its nutrients from the leaves back to the fruiting spurs. The nutrients that are known to migrate from the leaves to the spurs at the onset of leaf fall are nitrogen, potassium and phosphorous. These nutrients play major roles in bloom development and fruit set. If the orchard does prematurely defoliate due to lack of water, irrigate to encourage re-growth. This may reduce yields in the following year, but yield loss will not be as significant as not watering at all. If watering does not occur, not only will fruit bud differentiation be poor, the orchard will suffer from premature flower drop in late winter. The best advice is to avoid this situation all together by properly managing your water during the harvest period. 2. After irrigation, nitrogen fertilization is the most important cultural practice in an almond orchard. For most of our orchards, split nitrogen applications provide the most efficient use of nitrogen. A post-harvest nitrogen application can be of 20 to 40 pounds per application – dependent upon tree age- totaling no

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David Doll0 commentsAugust 24, 2009Diseases

Nematodes and Tree Growth

A grower made a request for a visit to his orchard due to poor growth by his replanted first leaf trees. The trees were replacing trees that were lost to heavy winds from the previous summer. Within the orchard, there were several different pollinators, and all of the trees were planted on Lovell rootstock. This orchard was located in a sand/loamy sand soil series, irrigated with solid-set sprinklers, with trees ranging from 1rst-15th leaf throughout the block. Often with replanted trees in an established orchard, it is very difficult to obtain vigorous growth. The trees usually are partially shaded out, receive either too much or too little water and fertilizer, and generally struggle with soil problems involved with replanting. The replants throughout the orchard were showing signs of low vigor, which include poor shoot growth, thinned canopy, and a general weak appearance (Pictures 1 and 2). The trees showed no other signs of disease on the scaffolds or trunk. Upon root excavation, a poorly developed root system was observed. There were no signs of fungal root infection or any other aggressive pathogens, vertebrate pests, or insects. Picture 1: A first leaf almond tree severely stunted by high nematode populations. Picture 2: A first leaf almond tree moderately stunted by high nematode populations. At this point, I decided to sample for plant parasitic nematodes. Sampling for nematodes is relatively easy: Remove the top 6″ of soil from the sampling locations, and use a soil sampling tube* to remove soil from the depth of 6″-18″ and place the soil in a bucket. Do this from 4-5 locations and mix the soil thoroughly within the bucket. Pull out 2-3 pounds of soil, place it in a labeled plastic bag, and place in a cooler or refrigerator until the sample can be sent to

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David Doll0 commentsAugust 18, 2009General

Almond Production Cost and Return Studies

Ever wondered what it costs to establish an orchard? Cost studies by the Agricultural Economics Department at UC Davis are available for the following regions:Conventional Micro-sprinkler Orchard in Northern San Joaquin Valley;Conventional Flood Irrigated Orchard in Northern San Joaquin Valley;Organic Sprinkler Irrigated Orchard in Northern San Joaquin Valley;Conventional Micro-sprinkler Orchard in Southern San Joaquin Valley;and Conventional Low Volume-sprinkler Orchard in Sacramento Valley.

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David Doll3 CommentsAugust 17, 2009Diseases

Armillaria Root Rot (Aka Oak Root Fungus) of Almond

A call last week revealed a disease issue in which there are very few solutions. A grower called with concerns of several trees recently collapsing from the heat. The decline has been relatively gradual until a week or go, in which the trees suddenly turned brown and are now dead (Picture 1). This problem has been ongoing for several years in which he would replant the trees after a tree site fumigation. The orchard was a 10th leaf Nonpareil, Fritz, and Aldrich orchard, planted on Nemaguard. Picture 1: Overview of an almond tree affected by a root disease. The orchard was in a clay-loam soil series, flood irrigated with district water once every 10-13 days, and appeared to be in good shape outside of the affected areas. Affected trees were usually surrounded by younger, replanted trees confirming the replanting that the grower has done in the area (Picture 2). Furthermore, the affected trees appeared to be in groups, and this was confirmed by a Google Earth image once I returned back to the office (Picture 3). All this suggests a biotic agent causing disease, and seeing a total collapse of the tree, I began to investigate the root system. Picture 2: “Hotspot” of area infected by Armillaria root rot. Picture 3: Google Earth Aerial Image of the orchard affected by Armillaria Root Rot. Please note the large holes within the orchard canopy indicating missing or dead trees. Upon root excavation, the tell-tale signs of Oak Root Fungus or Armillaria Root Rot became relevant. Hitting a surface root and scraping back the bark, the white mycelial fans became evident (Picture 4). Furthermore, the roots possessed a smell similar to what we would expect from mushrooms – similar to the smell of mushrooms in the grocery store. Further bark removal and scraping

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David Doll0 commentsAugust 11, 2009Horticulture

Preparing for Harvest

It looks as if harvesting will be underway for Merced County within the next week to 10 days, with the date occurring earlier for growers on the West and South Sides of the county. With harvest, there are many preparations that must be taken into consideration. Water Management:In order to determine the last pre-harvest irrigation, a target harvest date must be set. Approximately two weeks after the last irrigation are required to “dry down” the trees enough to minimize bark damage from shaking. This time period does vary upon soil textures, with sand and clay requiring less and more time, respectively. This depletion of soil moisture tightens the bark to the trunk and prevents damage from the shaker attachment. Also, as the season progresses, the bark adheres tighter to the trunk. Therefore, with an earlier harvest, the chances of shaker damage are increased. In soils of low water holding capacity (i.e. sand) it may be necessary to irrigate between the harvesting of the varieties. Proper water management between varieties is just as critical as water management before harvest because during this period the tree is developing the fruit bud for the coming season. Any moderate to severe water stress during this period will reduce the formation of fruit bud. Timing of Harvest:Harvest timing should be considered using the following criteria: – The need to avoid naval orange worm damage to nuts on the tree and ant damage once nuts are on the ground; – The ability to achieve maximal nut removal; – The ability to maintain yield and quantity; – Minimization of tree injury; – Availability of harvest equipment; – weather conditions that may cause crop loss or damage (i.e. rain). A few of these points are highlighted below: Damage caused by Navel Orange Worm and Ants:Early harvest prevents the

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David Doll7 CommentsAugust 3, 2009Insects, Irrigation

Shothole borer damage on Almond – Varietal Differences in Response to Water Stress

The water crisis on the West side of the valley has presented opportunities to see problems not typically observed in almond production. Many of these issues tend to be directly related to tree stress caused by lack of water, failure of salt leaching due to decreased winter rains, and chronic water stress from prolonged drought. Typical observations of drought stressed trees range include yellowing leaves and leaf drop in mild cases, wilted new growth during moderate stress periods, and poor crop set, thinned canopy, and scaffold die back in chronic cases. A visit was made to an Aldrich-Monterrey-Nonpareil orchard located near Los Banos, CA. All varieties were on Nemaguard rootstock. This orchard has been under moderate drought stress for the past two years as determined by the use of a pressure bomb. This year, the grower was again short on water and had to water at about 80% evapotranspiration rate for the season. The grower was concerned about clear gumming coming from multiple wounds on his trees. Orchard observations included those listed above for orchards suffering from chronic drought stress: poor vigor, thinned canopies, and reduced crop load. On the affected trees, gumming was seen extending form the graft union up to the scaffolds. The issue was predominantly found on Aldrich trees, with some strikes on the Nonpareil, and very few, if any, strikes on the Monterrey. Upon seeing the damage (Picture 1), it was very clear that it was shothole borer, Scolytus rugulosus, an insect that invades and lays eggs in the branches/trunks of stressed trees. Borer insects are able to push their eggs through the bark and into the tree. A tree that is healthy enough to elicit a response then gums profusely in order to flush the egg out of the tree’s tissue (Picture 2). This gum

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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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