Post Harvest Foliar Sprays

After harvest is a good time to apply a few different foliar nutrients to the trees before the leaves fall. Nutrient uptake occurs through wood and leaf tissues. Applying when leaves are still green and active increases the sprayed surface area, thus increasing the efficiency of the spray and uptake of the nutrients. Applications can be made when leaves are off the tree, but the reduced surface area leads to a reduced nutrient uptake.  Below are considerations to make in regards to a few commonly applied foliar nutrients. Boron. Studies have shown that a foliar spray of boron can increase crop set regardless of boron hull content. If the tree is deficient in boron, the resulting “yield bump” is greater than in sufficient trees, but the “yield bump” is still observed in sufficient orchards.  Two pounds of Solubor (20% Boron) applied with 100 gallons of water/acre is commonly used. This article detailing boron foliar sprays highlights the specifics. Urea/Nitrogen. Fall foliar applications of lo-biuret urea are thought to reduce the incidence of bacterial canker and bud drop within almond. It is thought that this reduction is due to an increase of tissue nitrogen content which may increase overall tissue health making it more resistant to bacterial infection. Fall Urea applied for bacterial canker prevention should be applied later in the season (i.e. first week of November) and at a rate of 100 lbs/acre. Studies have also shown that fall applied lo-biuret urea can increase yield. Although studies have not shown the yield increase to be significant, it has been observed in two trials. Both yield increases were observed with the lower end of urea use, between 10-25 lbs/acre. Higher applications of urea did not produce as much of an effect and in some cases led to foliage burn and leaf

October 21, 2011

Reports of Hull Rot

I have been getting a few calls regarding hull rot. I have covered this topic before (link to previous article), but some of the particular questions regarding the disease are answered below. What is Hull Rot?Hull rot is infection of the almond hull by two fungi, Rhizopus stolonifer (common bread mold), or Monilinia fructicola. These pathogens are common throughout the environment, and are, in this case, serving as opportunistic pathogens. Upon infection, they release toxins that are translocated into the fruiting wood, which kills the wood, causing crop loss. What do you mean by opportunistic pathogen?Once the hull splits, the perfect micro-climate for fungi is created. The hull is full of nutrients and water – the two things that fungi want from a host. Since the spores of these fungi are found throughout the air, they invade the newly split tissue, infecting, and completing their life cycle. By reducing the “home” for the fungi, we can reduce the number of hull rot strikes. These strategies include reducing the water and nutrient content of the hull. How can I prevent Hull Rot?Asking “How to prevent” is a good start. Prevention is the key to reducing hull rot strikes. Hull rot often affects high vigor orchards. Nitrogen should not be applied after kernel development is completed. This is typically the end of May, but this year it extended into mid-June. A slight to moderate water stress at the onset of hull-split should be applied. Applying both of these practices to the orchard has been shown in multiple research trials to reduce hull rot by 80-90%. Often times, this is all growers need to do to prevent severe hull rot issues. I tried those things, I still have hull rot!Severe outbreaks of hull rot have been observed. Last year, hull rot infections occurred in many orchards. I

August 20, 2011

Summer Foliar Disease Epidemics – Rust

I have received quite a few calls regarding rust and scab. Over the next few weeks, I am going to answer the commonly asked questions about these diseases and provide a management strategy to help reduce disease pressure for future years.In regards to a general overview of Rust, please see the following:Almond Leaf Rust – The Almond Doctor from April 10th, 2010,Almond Rust – UCIPM Website. I have rust all over my orchard. What can I do?Short answer – nothing. It is too late to expect control of the disease. Once the fungus infects the leaf and produces visible symptoms, that is a clear indication that the fungus has colonized the inside of the leaf. No fungicide completely penetrates the leaf surface, which makes it impossible to cure an infected leaf. Furthermore, spraying a fungicide upon seeing a disease epidemic will end up doing more harm than good. Since the fungus has completed it’s life cycle several times (Rust is a polycyclic disease), the population within the orchard is so high that making an application can lead to the selection of a fungicide resistant strain of rust. If every tree has rust, what can I expect?Defoliation. As the fungus colonizes the leaf, it begins producing spores which are the reproductive structures of the fungus. These spores are produced and move from an infected leaf to a healthy leaf. Upon complete colonization, the tree detects that the leaf is infected, forms an abscission layer which causes the leaf to fall from the tree. If enough leaves are infected on the tree, total defoliation can occur – and in most cases, is expected. What should I do?Since rust overwinters on the infected leaves in the form of teliospores (black spores found on the bottom of the leaves), it is important to destroy/remove all leaf

August 5, 2011

Almond Potassium Fertilization: Where did My Potassium Go?

A common question received from growers after they see their leaf sampling results is “How come my potassium levels dropped significantly from last year?” The short answer is that it was removed with last year’s harvest, but there are many complicating factors that should be taken in consideration. Potassium Removal from the Orchard System. Studies by UC Davis have shown that 76 pounds of potassium are removed from the orchard for every 1000 pounds of kernels harvested. From nutrient analysis of the fruit parts, 70-80% of the potassium removed by the harvest is within the hull, while the rest is within the shell and kernel. Potassium loss from the orchard can also occur through leaching. Leaching of potassium is reduced in soils with high exchange capacities, which includes loams, clays, and silts. Sands and loamy sands have a relatively low exchange capacity, lower amounts will bind to the soil particles. Furthermore, this bond is not as strong within acidic soils which can lead to leaching in areas that are over irrigated or received excessive rainfall. Since potassium and sodium have the same charge strength, strategies used to move sodium out of the rooting zone will also move potassium as well. These include applications of gypsum or other strongly charged cations to “flush” the system. Excessive applications of water applied as a leaching coefficient may also leach potassium. Proper Leaf Levels of Potassium. Since Potassium plays a large role in tree health, it is important to maintain proper levels of the nutrient within the tree. A critical leaf value of 1.4% has been established by the University of California and current research has suggested that levels excessively above this value do not increase yields. Recent field studies by Roger Duncan (UCCE Stanislaus) have demonstrated that leaf potassium levels in excess of

May 28, 2011

Using Urea Efficiently

Summary: Soil applied fertilizer is intended for root absorption by plants. Manage fertilizer nitrogen (N) to keep as much of it as possible in the root zone to maximize crop N uptake, crop yield, and protect the environment. To keep urea fertilizer N in the root zone 1) incorporate urea into the soil with water or cultivation within a day or two of application and 2) don’t over irrigate when incorporating urea using water. Inject liquid fertilizers containing urea (for example, UAN32) into irrigation systems in the middle third of the irrigation set. This delivers urea N evenly through the root zone, avoiding leaching that can occur when urea is injected too early in the set and limited root zone distribution when injected too late in the set. Background: Urea is the most commonly used dry nitrogen (N) fertilizer in the U.S. It provides half of the nitrogen in UAN (Urea Ammonium Nitrate) 28 or 32 liquid fertilizers. Dry and liquid fertilizers that contain urea have several advantages — relatively high N content (28-46% N), ease of handling and reasonable price relative to other N sources. However, nitrogen from applied urea can be lost from the root zone when used improperly, wasting money, reducing plant available N, and risking reduced crop growth and yield. The lost N can also be an environmental contaminant. Growers and PCAs should be aware of how to avoid N losses and get the most from urea fertilizer dollar. Within days of application, urea N can be lost from the crop root zone in two ways – through ammonia volatilization or urea leaching. This article will briefly describe how these losses can occur and how to manage urea to avoid them. The uncharged urea molecule (H2N-CO-NH2) breaks down in or on the soil into two ammonium molecules

April 13, 2011

Fertilizing Young Almond Trees – A Few Tips

A few questions come up every year in regards to fertilizing first, second, and third leaf trees. Since these trees are rapid growing, and in some cases, producing crop, adequate fertilization is crucial for growth. First leaf trees: As a guideline, I generally recommend no more than one ounce of elemental nitrogen per tree per application. Three to four (or more) applications using a general blend (i.e. 12-12-12 NPK) fertilizer per year will produce a nice result. Using a triple 12, this totals about 8 ounces of actual fertilizer applied per tree.  Applications should begin upon leaf out and continue about every 4-6 weeks.  To prevent any nitrogen burn, the first applications of the year should be less than one ounce while later applications should not be greater than one ounce. Although I know some growers are successful, I have observed enough tree damage to caution against using liquid based fertigation products for first leaf trees. It is easy to overdose the trees with nitrogen, especially in hot weather, causing tree die-back. I agree that using granular fertilizers is a conservative approach, but one that has been tested and used extensively over the years. Second leaf trees: The rootzone of 2nd leaf trees can be quite extensive, but is still limited in comparison to mature trees. Even if the grower is able to fertigate, I usually still like to see the first application to be granular. Why? In many cases adequate potassium and phosphate have not been applied in the previous dormant season, thus applying a 12-12-12 fertilizer will ensure at least some level of these nutrients as the tree begins the rapid growth period of April and May. Later applications can be made through the fertigation system. Again, follow the rule of one ounce per tree per year of growth. So,

March 25, 2011

Some Early Season Thoughts

I have been in a few orchards this past week and thought I would relay on some thoughts.1). Bloom. In comparison to last year, bloom seemed to last much longer. Some orchards I have been working next to are now entering petal fall. Their first blossoms opened up about 20 days ago. It appears that the trees hit full bloom in our area during the nice weather that we had last week. Hopefully this will aid in pollination and nut set. 2). Frost Damage.  Frost damage appeared to be pretty minimal (1-5%) in the 15 or so orchards I checked around Merced County. I have heard mumblings that damaged pistils and stamen from the extreme temperature may lead to poor pollination and nut set. At this time, it is hard to predict if this occurred and to what extent. Most likely this type of damage will become apparent during the flower drop and nut drop periods. Keep in mind that other weather issues may contribute to these drops making it hard to determine what caused what. 3). Fungicide Sprays. The threat of Brown Rot is still pretty high, especially with Butte/Padre orchards. This weekend we saw great weather for Brown Rot – over 60F and raining. The winds today have aided in the reduction of leaf wetness, thus reducing brown rot risk. If Sat/Sun/Monday’s rain event fell in the 10 day window from your last spray, it looks like you may be able to get through this week without too much worry – unless the weather changes! You have at least 10-12 days of protection after a fungicide spray. As petal fall approaches and we move into leaf out and nutlet formation, keep an eye out for shot-hole, jacket rot, anthracnose, and scab. Of these four diseases, scab requires the latest treatment

March 8, 2011

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

December 27, 2010

Understanding and Applying Information from a Soil Test: Part 2 – NPK

Part 1 of this series emphasized that soil testing is complementary to plant tissue testing and not a substitute in orchard management.  Considerations to ensure soil testing provides representative and useful information and interpretation of two common soil test parameters: 1) Saturation Percentage (SP); and 2) pH were also discussed.   This article will focus on the nutrients nitrogen (N), phosphorus (P), and potassium (K). Nitrogen Nitrogen occurs in soils as organic and inorganic forms and soil testing may be performed to measure levels of either. Nitrate nitrogen (NO3-N) is most commonly measured in standard soil tests because it is the primary form of nitrogen available to trees and, therefore, an indicator of nitrogen soil fertility.  However, soil concentrations of NO3-N depend upon the biological activity and may fluctuate with changes in soil temperature, soil moisture, and other conditions.  Nitrate is also easily leached with rainfall or irrigation so current soil tests may not reflect future levels of nitrogen soil fertility.  Table 1 provides guidelines for evaluating NO3-N soil fertility levels.  Table 1.  Guidelines for interpreting nitrate nitrogen (NO3-N) levels in soil test results. Fertility Level ppm lbs/acre1 Low <10 <36 Medium 10-20 36-72 High 20-30 72-108 Excessive >30 >108 1 Some laboratories report NO3-N as lbs/ac rather than as a concentration (ppm).  A soil bulk density is assumed in this calculation so the NO3-N fertility levels should be considered an estimate rather than an absolute level.   Ammonium  nitrogen (NH4-N) is also a plant available form of nitrogen in orchard soils and it can be determined with soil testing upon request.  In general, NH4-N is not determined and reported with a standard soil test.  Ammonium nitrogen does not usually accumulate in soil because soil temperature and moisture conditions that are suitable for tree growth are also ideal for conversion of

December 7, 2010

Preparing for the Dormant Period

Just returned from a field day meeting held near Firebaugh discussing pest and disease management strategies for the upcoming dormant season. I thought I would highlight a few points from the talks by Walt Bentley (UC IPM), Mario Viveros (Emeritus UCCE Farm Advisor – Kern County), and myself – David Doll (UCCE Farm Advisor – Merced County). I apologize for the brevity of the entry as I am preparing for a field trial due to be fumigated next Monday. Navel Orange Worm (NOW): Winter sanitation is critical to help reduce the overwintering population of NOW. In general, no more than two mummies per tree should be left in the tree. With some growers, complete removal of the mummies is performed. Most growers remove mummies. This is easily done on younger trees. As the trees mature and become larger in size, the task of sanitation becomes difficult, resulting in more mummies remaining within the upper canopy. This may explain why many growers see more NOW damage in mature blocks. Even though the trees may appear to be clean, a closer look usually reveals mummies still hanging in the tree. Peach Twig Borer (PTB): Scouting for hibernacula should be performed. There are several treatment options and timings for PTB. These include dormant oil sprays, bloom sprays with reduced risk products, and May sprays. See the PTB page on the UC IPM website for more information. Mites: European Red Mite and Brown Almond Mite will overwinter as eggs around the base of spurs. Spur sampling, which should also be done for scale, can help determine if treatment is needed. An oil spray outlines at the Mite page on the UC IPM website will suffice for most locations. Scale: The dormant period is the easiest time to treat for scale. Spur sampling can help determine the treatments needed. Check here for

November 16, 2010