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 Doll0 commentsApril 23, 2018General

Got voles? Perhaps anthraquinone is the answer.

Article written by: Roger A. Baldwin and Ryan Meinerz Department of Wildlife, Fish, and Conservation Biology, University of California-Davis, Davis, California Gary W. Witmer and Scott J. Werner USDA/APHIA/Wildlife Services-National Wildlife Research Center, Fort Collins, Colorado Recent research has shown we may have a new tool to protect trees and vines from vole damage. However, this product is not currently registered for such a use.  We need your response to know whether there’s enough interest in a new way to control vole damage to warrant seeking registration. Voles are short, stocky rodents that often cause extensive girdling damage to a variety of tree and vine crops throughout California.  Effective management has often relied on some combination of vegetation removal, exclusion using trunk protectors, and rodenticide application. However, all these management solutions have shortcomings. Vegetation removal doesn’t always eliminate all problems in an area.  Trunk protectors should be buried at least 6 inches below ground, increasing the labor required to protect trees and vines.  Rodenticide applications are generally not allowable within an orchard or vineyard during the growing season, when it is most needed.  See the following link for more details on voles and vole management:  http://vpcrac.org/files/4314/7612/1259/Meadow_vole_chapter.pdf. Clearly there is room for a new tool to be added to the proverbial IPM toolbox when it comes to managing voles in orchard and vine crops.  In recent experiments with a chemical repellent, anthraquinone, on citrus trees, we found that anthraquinone was highly repellent following trunk application (sprayed or painted on), with a >90% reduction in girdling damage observed following application regardless of the season when it was applied.  Anthraquinone exhibited substantial longevity, with no increase in girdling damage observed for the entire summer (5 weeks) and spring (6 weeks) sampling periods.  This clearly indicates substantial repellency for anthraquinone applications, with repellency to

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David Doll2 CommentsApril 5, 2018Insects

Put Leaffooted Bug Monitoring on Your To-Do List

Written By Kris Tollerup, UC IPM Advisor for the San Joaquin Valley Unlike many of the moth pests, we do not have an effective lure that acts to attract leaffooted bug (LFB) to a monitoring trap of some sort.  An LFB lure could be used in almond beginning at mid-March for detecting the pest when they first begin moving into the crop.  Unfortunately, development of a lure remains elusive; researchers out of the University of California, Riverside have worked on the issue for several years now.  They have recently identified compounds used by LFB for sexual and aggregation communication, but synthesis of the compounds has proven quite difficult. This means that good-old visual scouting provides the only viable option.  About this time (mid-March – early April) leaffooted bug begin moving into almond from their overwintering sites.  A caveat to this is that the recent cool weather may have slow their movement and caused some individuals to re-aggregate.  For instance, during early March, we observed signs that LFB had begun to disperse from overwintering sites; however, stopped short and reformed aggregations on nearby citrus trees.  This likely occurred due to cool, wet weather. With warmer weather certainly coming soon, begin monitoring in locations that historically have sustained damage and notably locations near pomegranate and riparian areas.  The bug typically prefers the sunny side of the tree and will rest on nuts on the outside area of the canopy.  Take about 15 seconds to visually inspect about 100 nuts per tree; monitoring 15 to 20 trees in a 5 to 10-acre area. Moreover, the University of California, Pest Management Guidelines recommends monitoring by examining nuts on the ground and in the tree for gummosis.  Keep in mind that gummosis from LFB or other stink bug feed appears clear while gummosis from other

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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 Doll2 CommentsFebruary 7, 2018Diseases, Irrigation

2018 Almond Bloom Considerations

2018 almond bloom is around the corner. This year will probably be one of the earliest almond blooms we have had in Merced County. This accelerated bloom is due to the warmer, sunny weather experienced through January. Depending on conditions following flowering, hull-split and harvest should also be earlier. Weather for the coming bloom period looks to be favorable for the San Joaquin Valley. Warm conditions (temperatures in the 70’s) and no rain in the forecast provides the conditions that are conducive for rapid flower development. Thankfully, these conditions will not favor disease. Early bloom sprays may not be needed for many tolerant varieties (e.g. Nonpareil), unless heavy dew and susceptible varieties (i.e. Butte) are present. Regardless of weather, a fungicide spray made at full bloom/petal fall should be considered. This fungicide should provide protection for brown rot, shot-hole and jacket rot. Of these three, jacket rot is one of the harder fungi to control with the modern fungicide chemistries as the strobilurins (FRAC 11) and DMIs (FRAC 3) are not effective. This spray timing will provide protection for any rain events that would occur within two weeks of application. Successive in-season sprays may be needed if the weather turns wet. Further information reagrding fungicide timing and efficacy can be found here: http://ipm.ucanr.edu/PDF/PMG/fungicideefficacytiming.pdf . Fungicide applications should be made at a time of day to reduce bee exposure. Applications later in the day will reduce exposure as bee foraging is decreased in the afternoon. If applying at night, allow enough time for the fungicide dry before bee foraging begins the next day. Also, avoid any addition of surfactants with the fungicide unless directed by the fungicide label. Many more management practices for bees can be found at The Almond Board of California’s website: http://www.almonds.com/pollination . The first irrigation will be tricky

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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 Doll3 CommentsDecember 15, 2017Irrigation

Is Winter Irrigation Needed?

The reduced late fall rains have led to relatively dry conditions throughout the State. Within the San Joaquin Valley, limited amounts of rain have fallen, with recorded precipitation around one inch in Merced. The lack of rain has led to a series of questions about winter irrigation requirements in which answers are included. Question (Q). Do I need to irrigate now? Answer (A). Evapotranspiration rates are very low and almond water use is even lower. A table has been included that has utilized the real-time evapotranspiration data (ETo), the corresponding crop coefficients (Kc), almond evapotranspiration (ETc) and rainfall for the MERCED CIMIS station. The need to irrigate should be based on almond water use, the amount of water that has been applied in the Late October through early December period, and rainfall. Week Starting: ETo Kc ETc (in) Rain (in) Nov 5th 0.48 0.69 0.3312   Nov 12th 0.38 0.69 0.2622 0.71 Nov 19th 0.34 0.6 0.204   Nov 26th 0.32 0.6 0.192 0.27 Dec 3rd 0.3 0.4 0.12   Total: 1.82   1.1094 0.98 Based on this example, ETc for the month of November and first week of December has been 1.11” with roughly 0.98” of rainfall. This suggests that an irrigation may be needed. If, however, any irrigation was applied in late October or November, most likely the water needs have been met. Water demands and rainfall are site specific. Determining the situation for the orchard location will be needed to determine localized water needs. When in doubt, checking soil moisture status may assist with the decision making. Q. I didn’t irrigate in Late October – December and rainfall has been limited, how do I apply the water? A. Irrigation sets should be shorter than 24 hours to reduce saturated soil conditions and the risk of Phytophthora. If

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David Doll2 CommentsNovember 28, 2017General

Observations from a Trip Down Under – The Australian Almond Industry

During the first two weeks of November, I was able to attend the once-every-four-years International Research Congress on Pistachios and Almonds. This meeting was held in Adelaide, Australia in which almond and pistachio researchers (as well as some growers) attended to discuss recent research within these crops. Prior to the conference, I toured some orchard operations in the Mildura area. These orchards had the look and “feel” of California orchards and  yields in the 2700-3000 lbs/acre. Through the visits and discussions with my various hosts, issues that many of the operations were trying to manage were similar but different to what we experience within California. Below are a selection that I found interesting and thought I would share. Good water management can compensate for limiting soils. Across all of the properties I visited, the soil profile was very shallow with  18-24″ of sand before hitting a limiting layer of clay. To make matters worse, the layer of clay often had a very high pH (>9) and boron (>3.0 ppm) – which would kill almond trees. These conditions reduced the rootzone to the sand profile which has limited water and nutrient holding capacity. To compensate for these “shallow soils,” most orchards are planted on a raised bed and irrigated daily with double drip systems to match the tree’s water demand for that day. The water applied does not exceed the holding capacity of the 24″ of soil to prevent root movement into the deeper toxic soil. This practice also prevents excess water from running off or creating a perched water table. This was an “eye-opening” experience for me. We generally have the luxury of deep soils within California in which we can irrigate deeply, less frequently. These irrigation practices, however, produced tree growth and yields which were comparable to California orchards.

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