Post Harvest Care for Almonds

We are mid way through almond harvest. As we finish up shaking our earlies and 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 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 units per application - dependent upon tree age- totaling no more than 10 to 20 percent of the total nitrogen applied to the orchard.

3. Pruning should occur after the harvest is completed. During this time it is easy to distinguish between old, diseased, dead and new wood. Remember to remove diseased branches 6-12 inches beyond the last sign of diseased tissue (i.e. canker). If possible, avoid pruning during the rain or if rain is within the 3-5 day forecast. Pruning cuts take at least 7 days to heal and can provide entrance for fungal pathogens.

The overall value of pruning itself has been questioned by recent UC research. Data has indicated that heavy pruning reduces the following crops yield and costs money to perform. When making the decision to prune, think of the real reasons you want to prune. Often times some of the ugliest orchards yield the highest. Please feel free to contact me if you have questions regarding pruning.

August 26th IPM Field Reporter from TRECE

Trece has released their IPM update in their biweekly "Field Reporter" e-newsletter. Here is the link:
Volume 15, August 26th, 2009 Field Reporter.

Wester Farm Press Article on Early Season Frost Damage

Here is the link to Western Farm Press's article titled "March frost damage lowers almond grower’s harvest prospects."

From the observations around Merced County after the early March frost event, it appeared that Butte/Padre orchards were the varieties most affected by the frost. Most growers experiencing a major loss had young trees (3rd-5th leaf) -- A few had a 100% loss. The severity of loss in younger orchards was most likely due to the lack of canopy cover which allowed the cold temperatures to "settle" around the tree. With larger trees, I noted that more damage was found in the tops of trees in comparison to ground level. Considering the bloom conditions, nut set was surprisingly heavy this spring - and it appeared the frost thinned the crop from a "great crop" to a "good crop" or "okay crop" for many growers.

What kind of damage did you all see around your orchards?

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 a processing lab. Do this from 4-5 locations randomly throughout the orchard.

There are four nematodes of concern for almond trees. They include Rootknot Nematode (Meloidogyne sp.), Ring Nematode (Criconemella sp.), Lesion Nematode (Pratylenchus sp.), and Pin Nematode (Paratylenchus sp.). These nematodes feed on tree roots, causing damage to the root system, preventing the uptake of water and nutrients. Nematodes survive as eggs in the soil and as adults and juveniles if a food source (roots) is present. It is important to remember that tree roots can live and host nematodes for several years after a mature tree has been removed. Therefore root removal to the maximal possible depth will help reduce nematode populations.

Submitted samples and resulting nematode counts from the visited orchard were as follows:

Results are shown as # of nematodes per cubic liter of soil.

Upon seeing the nematode counts, it was clear that the stunting was due to the high populations of root lesion and ring nematodes. The high population threshold for Ring and Lesion Nematode is 100 nematodes/cubic liter of soil.

Upon seeing these numbers, I advised the grower to take some sort of pre-plant measure to reduce the nematode populations. These include the application of the pre-plant fumigant Telone (1,3-dichloropropene), cover cropping with a non-host plant (i.e. True Sudan Grass), backhoeing and leave fallow for 1-2 years, plant a resistant rootstock, or any combination of the above. The goal of these pre-plant practices is to reduce the ring and lesion nematode populations below a 50 nematodes per cubic liter of soil - the lower the population, the better.

Typically, with this high of a population, I would recommend fumigating. Due to environmental regulations and his proximity to a school, however, the application of fumigants was not possible. We decided to remove the trees, backhoe to thoroughly mix the soil and remove the old roots, and plant a cover crop for one year. We then decided to try a few different rootstock that may have tolerance to Ring and Lesion Nematodes. These include the nursery available rootstocks of Viking (Tolerance to Ring, Resistance to Rootknot), Lovell (Tolerance to Ring, Susceptible to Rootknot) and Brights #5. A more extensive list of nematode resistant rootstocks can be found from Dr. Michael McKenry's report in the 2008 Proceedings of the Almond Board of California. I will let you all know how these rootstocks perform in the future years!

In general, the term "resistant rootstock" is used when the rootstock does not allow the nematode to feed/reproduce on the roots, while the term "tolerant rootstock" is used to describe a rootstock in which nematodes can feed on the roots, but the rate of reproduction is reduced or unknown.

Australian Almond Industry News Article

Almond industry blossoms: AUS
Wednesday, 19 August 2009
By FoodWeek Online @ 1:57 PM

Australia's almond industry has shown a 60 per cent growth in the value of exports this year.

Julie Haslett, CEO of the Almond Board of Australia, said the increase in the global demand for almonds has contributed to the growth of Australia’s horticultural exports.

“World almond consumption has been growing at an average rate of nine per cent per annum over the last 10 years," she explained. "Assuming a reduced annual growth rate of five per cent, the world’s demand for almonds is expected to exceed available supply within three years. The Australian almond industry is getting ready for this next surge in demand.”

Currently, 60 per cent of the Australian almond crop is exported to more than 40 countries around the world, making it Australia’s third largest horticultural export worth $120 million in 2008-2009. Strong export demand for Australia’s almonds is being driven by India and the Middle East, with the value of export sales to these regions having almost tripled since last year.

According to Haslett, domestic consumption of almonds has also increased in the last year.

“More than 90 per cent of almonds sold in Australia today are grown and produced by Australian farmers. Australians are eating more almonds, with domestic consumption having increased by over 10 per cent in the last 12 months,” she said.

Australia currently produces around 3 per cent of the world’s almonds. Over the next three years, as existing plantings reach full maturity, it is forecast that Australia will surpass Spain (8 per cent) to become the world’s second largest almond producer, behind California (82 per cent).

Australian almond plantings have increased from 3,750 hectares in 1999 to 27,300 hectares in 2008, making it one of Australia’s fastest growing horticulture sectors.

Haslett said the industry is undergoing rapid expansion.

“Less than 20 per cent of all Australian almond plantings have reached full maturity so there will be a significant increase in our home grown production within the next decade,” she said.

The production of Australian almonds reached 36,000 tonnes (kernel) in 2009. It is expected to increase to 80,000 tonnes by 2015, more than doubling the current production.

The key almond growing areas around Australia include Sunraysia in Victoria, the Riverland and Adelaide in SA and the Riverina region in NSW.
Click here to find out more!

During the current almond blossom season, which finishes in late August, residents can notice the spectacular almond trees in full blossom and pollinating bees at work.

“It is a great time for Australian farmers to show off the natural beauty and goodness of the almond crop,” Haslett said.

The Almond Board of Australia (ABA) is a non-profit, membership-based organisation representing the interests of Australian almond growers, processors and marketers.

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.

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 back of the white mycelial fans revealed revealed the fungal canker within the root tissue (Picture 5). Continued excavation revealed that the crown of the dead tree was severely infected by the fungus, with white mycelial fans found on the trunk and main roots.


Picture 4: White mycelial fans found on roots of an almond tree affected by Armillaria Root Rot.

Armillaria root rot or Oak Root Fungus is caused by the fungus Armillaria mellea. Armillaria root rot affects a large number of plant hosts and can be, as this orchard has demonstrated, a devastating disease in orchard settings. Armillaria is native to forests world-wide, and often is found in orchards that were established in once forested areas. Armillaria is considered a white rotter, or a fungi that breaks down lignin and other cell wall materials through the excretion of enzymes. In advanced stages of decay, the wood becomes light colored and stringy, with the cell wall material cellulose remaining. Honey colored mushrooms may form during a rainy period. The formation of these mushrooms, however, is inconsistent with orchard tree infection.


Picture 5: Fungal canker found on the root of an almond tree infected with Armillaria Root Rot.

Armillaria spp. is a basidiomycete, and can survive up to 100 years within woody debris found in the soil. Spread occurs when roots from a tree come into contact with the infested debris. Further spread can occur through rhizomorphs. Rhizomorphs may grow several meters through the soil away from the food source. Spread basidiospores does not normally occur.


Picture 6: Almond tree crown infected with Armillaria Root Rot. Note the large amount of white mycelial fans present within areas of removed bark.

Control for Armillaria root rot is relatively non-existent. Therefore pathogen exclusion is the greatest preventative measure. Equipment should be cleaned when moved between an infected and unaffected orchards. When replanting a field that has expressed the disease, all woody roots one inch (2.5 cm) in diameter should be removed. Fallowing the ground for one or more years is also recommended. When preparing to plant, fumigate the orchard with methyl bromide and plant a resistant rootstock within the infected area. It is important to note that fumigating will only kill the fungus within the treated area, and therefore it is needed to have the optimal conditions for fumigant movement within the soil. There is currently one known resistant rootstock - the plum rootstock Marianna 2624. This rootstock, however, has many other horticultural characteristics that are deemed unfavorable in almond production (i.e. incompatibility issues, suckering).

Installing of thick plastic root barriers down to a depth of 6 feet may help slow the spread of the disease. If this practice is used, it is important to place the barriers beyond the current zone of infection. Move at least a minimum of 2-3 trees away from the infected area. Some growers have reported the success of root barriers slowing the spread of the disease, but this practice is time intensive and has not yet been demonstrated by research.

August 12th IPM Field Reporter from TRECE

Trece has released their IPM update in their biweekly "Field Reporter" e-newsletter. Here is the link:
Volume 14, August 12th, 2009 Field Reporter.

Western Farm Press: Almond Varieties and Price Differential

Big price gap may alter almond variety choices
Western Farm Press
Aug 6, 2009 2:11 PM

Look for the wide variation between the prices growers receive for soft shell varieties, like Nonpariel, and hard shells, like Butte and Padre, to bring big changes in orchards later this year in Kern County, if not elsewhere in California.

“The price disparity between hard and soft shell almonds is way out of line,” says Vern Crawford, PCA with Wilbur-Ellis, Shafter, Calif.

“Growers of hard shell varieties are telling me that the first thing coming into their fields after harvest this year will be bulldozers,” he says “Unless their trees are producing 4,000 pounds per acre, they’ll be taking them out.

“Ten to 15 years ago, the thinking in the industry was to grow hard shells because you could harvest them without first having to spray for navel orangeworm. But, growers overplanted hard shells to the point where there are now way too many — now, the market wants soft shells.”

In fact, prices of 2008 crop hard shell varieties, with their smaller nuts, were historically low. At the same time, prices of Nonpareil Supreme grades and other large-size nut varieties continued to increase through this past spring.

In late July, for example, the difference in market value of these two types of almonds hit an all-time high. The wholesale price, Standard sheller run grade 36/40 Buttes, was about $1.15 per pound, while U.S. Extra #1 (20/22) Nonpareils were bringing around $2.40 per pound.

“If you’re not growing Nonpariel, you’re not making any money,” says a Sacramento Valley almond producer and processor. “Guys with a lot of debt to service are now in trouble, and many of them will be abandoning certain types of nuts.”

He attributes the higher prices for 2008 Nonpareils, in part, to production of fewer nuts, many of which were small and had to be sold as standards, which resulted in a bigger carryout of the smaller sizes.

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 damage caused by Navel Orange Worm (NOW) as it reduces the number of eggs laid on the shaken almonds. The NOW moth prefers to lay its eggs on almonds that are still within the tree canopy, thus almonds that are shaken before the emergence of the third generation larvae will have less damage than almonds shaken after this period. Growers of Nonpareil should begin the harvest before this upsurge in worm pressure begins. Later harvesting varieties may have more exposure to NOW, but an earlier harvest of worm-infected Nonpareil nuts will still reduce worm pressure for these later varieties.

With Ants, it is just the opposite. The longer the nuts are on the ground to dry, the more ant damage can be expected. Many growers therefore place baits (Pyriproxyfen, Abamectin, and/or Methoprene)6-8 weeks prior to harvest to selectively reduce the ant populations that fed on the almonds. If the populations of the almond feeding ants are still high at harvest, it is possible to control ants by making an application of broad spectrum insecticide (Chlorpyrifos) to the soil surface to kill any emerged ants.

Achieving maximal nut removal:
The formation of an abscission layer between the nut and peduncle is needed in order to shake the almonds from the tree. Once the abscission layer has formed, nut removal may be as good as it is going to get. Letting the hulls dry too long on the tree may cause a higher frequency of stick-tights, either causing a loss of crop or requiring a second shake. A good, properly timed shake should remove about 99% of the nuts.

Determining when to begin harvest:
To determine the start time of the harvest, strike a tree limb and see how easily the nuts come off. If conditions appear to be about right, test shake a few trees. Once 99% of the nuts are shaken from the test trees, begin shaking the entire orchard. Determining when to shake the whole orchard should not just rely on nut removal. upon shaking, observe the bark to see if any damage has occurred. Check for signs of bark breakage, water soaking, or wet lines on the shaker pads. If any sign of tree injury occurs, wait a few days and try again. Bark damage is one of the main means of entrance of the scaffold and trunk pathogen Ceratocystis fimbriata.

Mechanical shaking can be tried as soon as the interior orchard trees reach 100% hullsplit. For mature trees, tree nut removal is maximized when shaking at 100% hullsplit. Once the nuts are shaken to the ground, a hullable product should be expected within 2 weeks.

July 29th IPM update from Trece

Trece has released their IPM update in their biweekly "Field Reporter" e-newsletter. Here is the link: Volume 13, July 29th, 2009 Field Reporter.

Almond Articles from Western Farm Press

Western Farm Press has published a series of articles relevant to almond production. Click the title to be linked to the article on the Western Farm Press website:
1. Drought Management and Almond Research, Bob Curtis, Aug 5th, 2009;
2. Enhancing Honey Bee Habitat, Dan Bryant, July 30th, 2009;
3. Almond Pest Management Courses, Meeting Announcement, July 30th, 2009;
4. Climate Threatens Fruit and Nut production, July 23rd, 2009;
5. Tree Fruit, Vine, and Nut Depreciation bill, July 22nd, 2009.

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 Aldridge-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 Aldridge 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 response is a rapid response to a wound, not an infection, and therefore clear gum is exuded.

Picture 1: Overview of damage done to an almond tree by the shothole borer, (Scolytus rugulosus).

Picture 2: Shothole borer damage done to almond. Profuse gumming is in response to wounding of tree tissues by the borer.

Removal of the bark from around a gumball reveals a small hole (Picture 3). This hole was probably formed by the female beetle laying her eggs (Picture 4).

Picture 3:Hole made within trunk by the ovipositing female.

Picture 4: Female shothole borer laying eggs in the branch of a tree.

Shothole borers can kill trees, but typically damage this severe is not present in a vigorous orchard. If eggs laid within the tree hatch, the borer larvae will feed on plant tissues, creating a gallery which could girdle the tree and cause tree collapse (Picture 5). Eventually the larvae will mature and emerge leaving exit holes which resemble damage done by a shotgun (Picture 6). Of another concern is the introduction of fungi who gain entrance through the wounds caused by beetle entrance/exit. These fungi may also girdle limbs and cause branch or tree death.

Picture 5: Bark removal from branches affected by shothole borer damage reveal "galleries" or tunnels made by feeding larvae.

Picture 6: Emerged mature adults leaves exit holes resembling damage caused by a shotgun.

Control strategies for of the shothole borer are very limited: chemical controls can work, most are not registered for use, and the others appear to be more of a hassle than worth in an orchard setting. Infested branches should be removed from the orchard and burned. Traditionally, insecticide mixed with latex paint was applied tot he trunks of the trees. This practice is no longer available for use: the insecticide previously used are not labeled for this practice. Therefore, the main factor in reducing shothole borer damage in an orchard setting is to reduce tree stress. Stress trees attract shothole borers either through by increases infrared radiation or the emittance of kairomones.

In this orchard, the tree stress was most likely due to lack of water. Using a pressure bomb, six trees of each variety (Aldridge, Nonpareil, and Monterrey) where pressure bombed in order to determine the differences in varietal susceptibility. The pressure chamber average results were as follows (Remember: the more negative, the more stressed): -17.3 bars, -16.5 bars, and -15 bars for Aldridge, Nonpareil, and Monterrey, respectively. According to the UC general guidelines, all of these trees are moderately stressed, with the Aldridge approaching severe stress. It is also worth to note that the variety that is least affected by shothole borer was also the variety that was least stressed. This provides evidence for the stressed tree hypothesis proposed above.

This brings to light another question: Why do varieties within the same orchard, same irrigation system/program, and same soil profile differ so greatly in their tree stress? This question remains to be unanswered but probably has something to do with one or more of the following possibilities:

1. Varieties differ in their temperature ranges for stomatal activity. Some varieties may have stomates active during higher temperatures causing a higher rate of water loss (i.e. Aldridge varietal may maintain stomatal activity when temperatures reach 90 degrees F while Monterrey varietal shuts down stomates at 88 degrees F).

2. Varieties differ in their vigor. Some varieties may "pump" more photosynthate into the root system, thus increasing the root mass and depth, providing more access to soil moisture.

3. Varieties may differ in their tolerance of water stress. Varieties react differently to a mild, moderate, severe water stress, resulting in a reduction of time that stomates are open, thus reducing water loss (i.e. Aldridge varietal may maintain stomatal activity when moderately stressed while Monterrey varietal shuts down stomates when moderately stressed).

What do you all think?