David Doll6 CommentsFebruary 6, 2019General, Horticulture

2019 Almond Bloom Considerations

Almond bloom is just around the corner. This “start” to the season is an important period for almond production as flowers require reasonable weather conditions for pollination, fertilization, and eventual fruit set to occur. With that in mind, below are a few considerations for this period. Rain or conditions favoring dew can increase the amount of disease. Pathogens affecting almond flowers are ubiquitous in the environment, and therefore the condition that influences infection are periods of leaf wetness. Fungicides should be applied to protect the flowers from rain-splashed spores and subsequent infections. Newer class fungicides can move into the upper cell layers of the flower and kill infections, but this “reach-back” potential only provides about 2-3 days of “cure” after a rain event. Start the spray program with fungicides that are most effective for blossom diseases, but provide limited protection for petal fall and spring-time diseases. This typically includes the FRAC groups 1 and 9. As bloom progresses into petal fall, other fungicides should be considered to manage anthracnose, green fruit rot, shot-hole, and scab. FRAC groups 3, 7, 11 or combinations of these products should be considered. Remember to rotate away from fungicide FRAC groups used in previous sprays. This will help reduce the formation of resistance within pathogens, increasing the “shelf life” of a fungicide. To assist with this, especially if rainy conditions are expected, consider utilizing a broad spectrum material at petal fall or shortly after this period to provide the ability to use strobilurins and DMIs (FRAC 11 and 3) for scab and rust control. Some good rotational, broad spectrum products include chlorothalinil (FRAC M5), Ziram (M3) or Captan (M4). Don’t forget about the bees. Honeybees are brought into the orchard to provide pollination services – a requirement for production for most California type almond varieties

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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 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 Doll0 commentsFebruary 18, 2013Horticulture

Cold Weather Expected

A cold front is moving into the area this coming week. Even though many areas are still at 5% or less of almond bloom, I thought providing some background information on frost protection and mitigating strategies may be useful if trees are more advanced within your area.

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David Doll0 commentsMarch 6, 2012Horticulture

Frost Prevention in Almonds

Windy and cold conditions are forecasted for the next few nights. The temperature is expected to drop just below freezing, indicating the possibility of an advection frost. If temperatures stay above 28F, damage should be minimal. Never-the-less, windy conditions will remove heat from the orchard, reducing the effectiveness of frost prevention measures. Here is further information regarding frost damage and control:General Information on Frost Damage PreventionRates of Irrigation to Prevent Damage Basically, application of water via irrigation will increase the heat within the orchard, reducing frost damage. Temperatures will dip to their lowest just before dawn, but irrigation should occur before this time in order to increase heat within the orchard canopy.

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David Doll0 commentsFebruary 24, 2011Horticulture

More info in Regards to Frost Protection

I received the following question and thought the response was important enough for an entry:“… The forecast shows that 28 and but also chance of rain for the same night. Does that mean we will moisture from the ground to hold the temperature up. Would that mean no irrigation is needed?” Response:Most likely, it will be a clear night in order to drop to 28F. If not, the event would be considered an advection frost event, which are very difficult to provide protection as the wind displaces the heat gained by the various strategies. It is correct to assume that if the surface of the soil is wet from rain, that irrigating more to wet the soil surface will not provide too much of a benefit – i.e. flood and/or drip systems. This is especially true if the surface water freezes. Once the water freezes, heat will no longer be released. Keep in mind that drip system lines may actually freeze if volumes are not high enough (less than 15 gallons/minute/acre). If volumes over this rate can be applied, drip systems may provide some benefit. In regards to micro-sprinkler or solid set systems, applying water during the night will provide a heating effect even with a wet soil surface. This effect is due to the heat that is 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 avoid freezing of the spaghetti tubing/ irrigation lines. These rates were determined through research conducted by Joe Connell (UCCE Butte County) and Richard Snyder (UCCE Specialist).

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David Doll0 commentsFebruary 18, 2011Horticulture

Cold Temperatures Expected this Weekend

Cold weather is expected for Saturday night. As of now, temperatures are expected to drop below 32F. If the weather is as predicted, temperatures will not drop much below 30F. At this temperature, almond buds, blossoms, and young fruit should be safe. I wrote an entry last year covering this topic as well as frost damage prevention. In brief: Almond Susceptibility to Frost. Generally speaking, the further the tree advances out of dormancy, the more sensitive to frost it becomes. A dormant tree is very tolerant to cold temperatures, while small nutlets are very sensitive to frost damage. At this point of the growing season – petal fall to early nutlet development – temperatures below 26F will cause significant to total loss of the almond crop, while temperatures above 28F will cause minimal damage to the crop. The small difference of 2F makes the difference, and is why frost prevention strategies can be used to reduce crop loss.Frost damage prevention. Growers can manage their soil moisture and ground cover to help reduce frost damage from a radiation frost event.Click here to view the entire article.

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David Doll5 CommentsMarch 9, 2010Horticulture

Orchard tasks to help prevent frost damage

A light frost event is predicted for Tuesday and Wednesday night. Last year, an unexpected frost event caused a lot of damage to almonds throughout the San Joaquin Valley. Today’s entry will focus on frost protection. Types of frost. There are two major types of frost events that occur throughout California. An advection frost occurs when a cold front moves into the region, displacing the warm air. These events are rare and will have temperatures dropping below freezing even though the it may windy. They are very difficult to protect against due to the rapid displacement of heat from the orchard. Radiation frosts are more common. They are characterized by clear skies, calm winds, and temperature inversions. These frost events occur due to the gradual loss of heat from the orchard. Almond Susceptibility to Frost. Generally speaking, the further the tree advances out of dormancy, the more sensitive to frost it becomes. A dormant tree is very tolerant to cold temperatures, while small nutlets are very sensitive to frost damage. At this point of the growing season – petal fall to early nutlet development – temperatures below 26F will cause significant to total loss of the almond crop, while temperatures above 28F will cause minimal damage to the crop. The small difference of 2F makes the difference, and is why frost prevention strategies can be used to reduce crop loss. Frost damage prevention.Assuming that the orchard has already been planted (Further information regarding site selection for frost prevention can be found in the UC Almond Production Manual), Growers can manage their soil moisture and ground cover to help reduce frost damage from a radiation frost event. Moisture within the soil retains heat. This heat is then radiated up into the trees during a cold night. Dry or cultivated soil usually

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David Doll0 commentsFebruary 16, 2010Horticulture

Checking Thermometers to Monitor Frost Temperatures

By: Maxwell Norton (UCCE Merced) During frost season it is important to precisely know how cold it gets in various parts of your orchard or vineyard. Affordable minimum recording thermometers are available through farm stores and are usually pretty accurate but you need to check them yourself every year because they can “drift” up or down over time. The “U” shaped minimum-maximum recording thermometers are usually accurate at one end or the other but rarely both. Don’t use a “freebee” or a decorative thermometer. Fill a plastic bucket up with ice. Add enough cold water to make a slurry. Shake the bucket gently so the slurry stays loose. Insert the thermometers into the ice & water mixture so that about 2/3 of the thermometer is submerged. If it is an electronic sensor and it is waterproof, make sure it is completely submerged. Electronic devices may have a separate procedure for calibrating – check the instructions or their web site. Let the thermometers sit for twenty minutes. Pull the thermometers out one by one and immediately note the temperature. In a mixture of water and ice, the temperature should be 32F. If not, mark a correction factor on the thermometer. If it is more than 2-3 degrees off, you probably should not use it for something as critical as frost management. Thermometers should be placed in the low spots in the field that get the coolest. They should be away from and preferably up-wind from buildings, blacktop, or anything that might radiate heat at night. The thermometer should be about four feet off the ground and not be exposed to the sky – a simple “shelter” consisting of a board to attach the thermometer to with a cover extending 6-8 inches over the top works. Position the thermometer horizontally with the

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