David Doll4 CommentsDecember 5, 2018Horticulture

Pruning: The Basics

Pruning is the practice of removing unwanted branches from the tree. Pruning can be broadly categorized to two types of cuts: heading and thinning. Heading cuts remove the terminal bud from the limb. This removes the “control center” and creates a varied response depending on the tree growth stage. Thinning cuts remove an entire limb is removed at a specified junction. This, as long as it is made in a position of low light, will often lead to little regrowth, regardless of when the cut was made. When making heading cuts, the time of the year matters. Dormant heading cuts often lead to an increase in vegetative growth the following spring. They are sometimes considered “invigorating cuts,” and can also be employed to redirect growth of a limb. In-season heading cuts will slow growth and are considered de-invigorating. These cuts slow canopy development as the tree has to redevelop the vegetative buds to push new growth. If timed appropriately, in-season heading cuts can lead to thickening of limbs and reduced breakage from wind and crop. Regardless of when they are made, heading cuts create branching. The growth response from a dormant heading cut depends on “how hard” the tree was cut back. The more proximal the cut (towards the trunk of the tree), the more vigorous the growth response. These growth responses originate out of epicormic buds, or buds that lay dormant within the wood of the tree. When these buds push, they grow without regulation and have very long internodal distances. This leads to very rapid, vertical growth that often has few fruiting positions. Thinning cuts can be made any time of the year. These types of cuts remove entire limbs and are commonly used to remove limbs from the lower canopy. Too many thinning cuts, however, can increase

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David Doll3 CommentsApril 30, 2018Horticulture

2018 Almond Frost Event – What was learned

Field note written by Allen Vizcarra, Staff Researcher for UC Cooperative Extension, Merced County Almond frost damage begins when temperatures in orchards drop below approximately 28 °F, but the exact temperature depends on variety. There are a few but important practices to mitigate frost damage in orchards. Common practices include running irrigation water, mowing vegetation, and increasing air flow to the orchard (e.g., using fans to mix cold and warmer air). Implementing any or all these strategies could be just enough to increase the temperature by 1 or 2 °F, which can be enough to avoid or mitigate frost damage. Almond sensitivity to cold temperatures progressively increases from buds to small nuts, emphasizing the concern for cold temperatures during and after bloom. This past year, we observed survivability of almonds within orchards that were colder than the critical temperatures. This could be due to an increase in flower set of the remaining flower buds that opened after the freeze event. It could also be due to improper estimation of the cold temperature thresholds that we use as guidance. Finally, and more than likely, the varieties commonly planted within the field may be more tolerant to cold temperatures than we thought. Many of these were not ever evaluated for cold sensitivity. A recent observation near Chowchilla, CA in an orchard using micro sprinklers was the formation of icicles hanging from the lower canopy. There are always questions regarding if this is good or bad. The answer is a “it depends,” but generally it is better for the flowers in the upper canopy than the ones that are covered in ice. The icicles formed when irrigation water hit parts of the canopy by either unleveled sprinkler (i.e., spray not orientated perpendicular to the ground) or from a high angled spray pattern. Water

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David Doll2 CommentsMarch 30, 2018General, Horticulture

2018 Spring Update

Spring conditions over the past week have finally turned favorable for growth. After a very warm winter, a long bloom with periods of cold weather, followed by a few weeks of wet weather, trees are starting to grow and nuts are beginning to size. These weather conditions have led to a few interesting observations and considerations for the spring. Leaf lesions caused by bacteria. Observations from several fields have yielded the occurrence of bacterial leaf spots. These spots are thought to be caused by Pseudomonas syringae, the same bacteria that causes blossom blast. Lesions are often varied in shape and have a distinctive yellow halo. Generally, the tree recovers after shedding a few leaves. Conditions can worsen if rains persist. Copper treatments to prevent may do more harm than good due to tree sensitivity. Lesions can be easily confused with herbicide drift or shot-hole; review application history to determine if these could be potential causes. Vegetative bud failure. Just as we observed in 2015, we have been observing vegetative buds within last year’s growth failing to push. This “bud failure” is not the same as non-infectious bud failure (crazy top) as future generations of buds will be healthy. Although we are unsure of exactly why this type of bud failure occurs, we believe it to be due to a reduction of localized carbohydrates from the December and January temperature ranges. Explained simply, warm winter days and nights below freezing increase the rate of respiration, leading to reduced carbohydrates to assist with bud break. If levels drop too low, buds can die. Often, healthy buds below the affected area will grow and hide the damage that occurred. Sometimes, buds will break later than normal. More rain. Mid-range forecasts are predicting rain for the end of the first week of April. These

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David Doll2 CommentsMarch 9, 2018Horticulture

Frost Damage Effects: Points to Consider for 2018

The frost event from the week of the February 19th impacted almond production Statewide. Temperatures dropped in many areas below the critical temperatures. This was compounded with a low dew point which made frost mitigation strategies difficult. Damage has been reported from just about all production areas across the State. Damage reports at this time are challenging to make. Flowers and young nutlets should be checked to see if they have been killed. This is indicated by browning tissue on the inside of the tissues/ovary. This article from 2011 covers a variety of symptoms that may be observed. Damaged flowers and nuts will drop from the tree as the crop begins to set. This may take several weeks and may not be evident until the nuts begin to increase in size. Many will most likely fall off with this upcoming rain storm. It is a common misconception that the tree will compensate for crop loss with an increase in set percentage of the surviving flowers. This is not exactly true. There is some mild compensation due to a slightly higher set percentage of undamaged buds (~2% or so increase) as well as a gain from increased kernel size due to more energy directed to the embryo during the period of cell division. These two factors, however, are not enough to compensate for flower loss that may have occurred during bloom. Although many often hope, it is unlikely that the late blooming flowers will set as they often lack the energy within localized tissues to form a viable nut. Once a damage estimate can be made, the season plan should be adjusted. Nitrogen rates should be reduced if losses occurred. Depending on the severity of crop loss, certain pest management practices may also be omitted. These include late season bloom/petal fall

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David Doll8 CommentsFebruary 17, 2018Horticulture

Almond Frost Warning and Protection Methods – 2018

The upcoming week will see temperatures drop to the mid-20’s. With the current almond crop stage, damage and losses may occur if mitigation practices aren’t utilized. Below is a list of previously written entries to provide guidance on when to start, how much to irrigate, and other practices to utilize to mitigate frost damage. The point to turn on irrigation is dependent on dew temperature and the expected low temperature. Starting the irrigation too late when the dew temperature is low can increase the risk of damage. Turning off too early can also increase the risk of damage. Techniques utilized to determine when to start and turn off irrigation usually revolve around the use of a “wet bulb.” More can be found in this article written by Dr. Richard Snyder, a bio-meteorologist at UC Davis. Irrigation application rates need to be high enough to provide an increase in air temperature. Application rates should exceed 30 gallons per minute per acre. Rates less than 15 gallons per minute per acre may lead to freezing of irrigation lines/spaghetti tubing. More on this can be found within this article. The critical temperature of damage will vary by bloom stage and variety. Tests to determine the sensitivity of some varieties has been conducted and can be found on this table. At full bloom, temperatures at or below 27-28F  can cause crop loss. As trees leaf out and nuts begin to develop, the sensitivity to cold temperature increases. There are a few practices that should be implemented to reduce damage. These are outlined in this article. Please note that in flood and drip-irrigated orchards it may not be possible to have high enough discharge to have a warming effect of the water, but adding moisture to the soil can increase the warmth of the field

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David Doll6 CommentsJanuary 19, 2018Horticulture, Insects

How late can almonds be shaken for winter sanitation?

Winter sanitation is critical in managing navel orangeworm (as well as some other diseases) within almonds. Removing this past year’s remaining almonds – also known as mummies – is a time intensive process. Sanitation occurs by winter poling crews or by re-shaking the trees. This “winter-shake” is a quick way of removing the majority of the mummy nuts and, in high mummy-count orchards, is often used in combination with poling crews. With a dry November and December, winter-shaking of almonds have been delayed. This has led to several questions regarding how late almonds trees can be shook. Work done over 35 years ago by Steve Sibbett and colleagues found no impact on nut set, yield or size when winter shaking as late as January 31st. This was approximately 8 days prior to pink bud. The author concluded that shaking should be concluded by January 25th within the southern San Joaquin Valley, while it could be a week later in later blooming areas. Cited article: http://calag.ucanr.edu/archive/?type=pdf&article=ca.v037n07p20 When winter-shaking, it is common to see buds on the ground. Even though there may be several hundred buds, a reduction of yield shouldn’t be expected. This is due to the large number of buds that are present on an individual tree. For example, in a 3000 lb/acre mature orchard with 140 trees/acre, approximately 40,000 buds are on each tree, based on a 25% fruit set. Even if substantially higher buds drop from the tree after shaking, observations from several researchers suggest that the tree would compensate with a higher set percentage. Being that this research is over 30 years old, there is a need to update the work. Modern shakers are more effective as well as adjustable. It may be possible to shake closer to bloom without effect (although 8 days prior to pink

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David Doll0 commentsSeptember 9, 2017Horticulture, Irrigation

Almond Postharvest Management: Water Demands

After the hustle of harvest, it is easy to think that the orchard work is nearly wrapped up for the year. With almonds, this isn’t the case. Research over the past 30 years has identified the postharvest period as the primary development period that impacts next year’s crop. Not surprisingly, much of this work has shown proper irrigation practices during this period being the major factor. For this article, the post-harvest period will be defined as mid-August through early November. During this period, the trees can demand an estimated 12-15″ of water based on location and weather. Roughly 70% this demand is from the six weeks immediately after harvest – when the days are hot and longer (see included table). Shorting trees of water during this period of high water use (mid-August through September) has been shown to significantly reduce next year’s yield. In fact, research by David Goldhamer and Elias Fereras have found that the first 8″ of water applied during the postharvest period is the MOST CRITICAL water applied to maintain orchard yields. Why is this?  Almond floral bud differentiation, unlike other Prunus spp.,  begins in mid- to late-August and continues through early September. Water shortages during this time reduces carbohydrate development, leading to less energy being able to be directed towards the creation of next year’s flowers, affecting both flower quality and quantity. This, in-turn, leads to an overall reduction in fruit load. Practices should be employed to keep leaves on the tree through the postharvest period (early November).  Reducing tree stress through the harvesting process is the first step in maintaining highly productive trees. This includes being timely with shaking so trees are stressed for a minimal amount of time and understanding the amount of soil moisture and the rate of use – which includes taking

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David Doll3 CommentsJune 23, 2017Horticulture

What influences hull-split timing?

Hull-split often occurs around the end of June though the first week of July within the San Joaquin Valley. The start and duration of hull-split is influenced by the variety, weather, and tree stress. As many are aware, the variety has the strongest influence on hull split initiation and progression, but this article will focus on the influence of weather and tree stress. Most people believe the weather experienced in mid-June strongly influences the start of hull-split. Research has indicated, however, that this is not true. Work by Ted DeJong (UC Davis Plant Sciences), has found that the beginning of hull-split (which is indicated as 1% hull split) can be predicted by weather conditions experienced during the first 90 days after bloom. Cooler conditions experienced during this time will lead to a later hull-split, while warmer conditions result in an earlier split. Temperatures in the latter half of the spring and early summer have a minimal influence on nut progression, regardless of being warmer or cooler than normal. The model can be found at http://fruitsandnuts.ucdavis.edu/Weather_Services/almond_hullsplit_prediction/ and can be applied using localized CIMIS data. There is some evidence to support that tree stress and nutrient status influences the duration of hull-split. Stress in June decreases water content within the hulls, which means a faster drying time when they begin to split (think of hull-split progression like a bell-shape curve – stress in June shortens the x axis).  This is often related to high heat experienced in June, which leads to tree stress due to inability to properly manage the irrigation or the application of regulated deficit irrigation (RDI). Nitrogen status of the tree also influences the rate of split, in which trees having a higher nitrogen content have a longer duration of hull split. Often vigorous orchards are grown with minimal

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David Doll4 CommentsMay 13, 2017Diseases, Horticulture

Almonds Exuding Clear Gum

Several calls about gummy nuts were received this week. Of concern are nuts that are oozing clear gum along the suture or side of the hull. There are many potential causes of clear gumming, which include bug damage, boron deficiency, and internal causes from an expanding kernel. Bug damage. Most people are aware of leaf footed plant bug damage. Feeding by this insect can kill the almond embryo when the insect inserts its needle-like feeding tube into the nut. This often leaves a small pin-prick hole which results in clear gum being exuded 3-10 days after feeding. Although the risk of the bug killing the embryo decreases after shell hardening, there can be some staining of the kernel. As the season progresses, feeding by plant bugs decrease, while stink bug feeding can increase. These insects do not have long enough mouth parts to feed on the kernel, but feed on the fruit instead. They often have several feeding points on a single nut. All of these may gum. Severe feeding by stink bugs may impact kernel quality, but the economic threshold of these insects is unknown. Boron deficiency. Too little boron can cause gumming. Usually a clear gum exudes out of the side of the nut or suture line. When cutting the nut open, the kernel is often discolored with copious amounts of gum. These nuts often drop from the tree, and if not, the gum can harden and misshape the kernels, impacting kernel quality at harvest. Another sign of deficiency is a low crop set. Tree boron status should be determined by hull analysis – which has been discussed previously.  This type of deficiency is common in areas that use clean surface water and have not applied any boron to the soil. Physiological- expanding kernels. Occasionally, almonds can gum for no apparent reason.

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David Doll9 CommentsFebruary 23, 2017Horticulture

Freezing Temperatures:Almond Frost Sensitivity

There is a frost risk for the next few nights with temperatures dropping into the high 20’s and maybe lower. If these forecasts are true, crop loss could be experienced within colder areas of almond orchards. As written previously, there are some tasks that can be performed to help reduce the risk of frost damage. These include mowing the cover crop or residual vegetation to allow radiant heat form the soil to move into the canopy, use of sprinkler systems to apply water which warms the orchard, or utilization of equipment or fans to help move warmer air into the orchard. All of this is to help increase orchard temperatures by 2-3 degrees. The risk of frost increases as almonds break dormancy and begin development. Dormant buds are relatively tolerant to freezing conditions, but sensitivity increases as flowers develop from pink bud to full bloom, then into nutlets. The following figure selected from “The Almond Production Manual,” developed by Joe Connell and Richard Snyder, demonstrates the change in sensitivity. Essentially, sensitivity does vary slightly by variety, but a 50% or greater of crop loss can be experienced during bloom when temperatures drop to 27F for 30 minutes. After petal fall, this temperature threshold increases to 28F. Colder temperatures can cause significant crop loss. Implementation of frost protection measures should be considered when temperatures approach freezing as orchards are often colder than forecasted temperatures. Mowing must be done prior to the frost event. Irrigation systems applying water during the night will provide a heating effect even with a wet soil surface due to heat being released off the water as it freezes. In essence, with these systems, more water equals more protection. Targeted amounts of water should be 30-40 gallons per minute per acre. Minimally, water should be applied at rates higher than 15 gallons/minute/acre to

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