David Doll2 CommentsMarch 5, 2023General, Horticulture

Frost damage to almonds

Almonds are susceptible to frost once they begin to flower. As a flower progresses through bloom (i.e. dormant > pink bud > full bloom > petal fall > small fruit), it becomes more susceptible to cold temperatures. Frost killed flowers/small fruits are easy to identify as the color of the tissue changes. Flowers affected by bloom often have wilted petals or blackened pistils. At petal fall and later, the damage often appears as brown or black tissue within the ovary. This can be identified by cutting the flower/nutlet in half. The photo provides a comparison of flowers affected by frost and a healthy flower. Note the darkened, off-color tissue of the three flowers on the right. All of these have been killed by the frost. Flower sensitivity to cold damage has been studies. Additional information on this can be found here.

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David Doll4 CommentsMarch 6, 2022General

Considerations for March 2022

March is a month full of surprises. Weather can be highly variable, with rain, risk of frost, and heat waves all being possible. Below are some points to consider as the season progresses. Ongoing frost concerns. Frost conditions can occur through the end of March. Maintain a watchful eye on the weather conditions to reduce the risk of any frost event. Critical temperatures after petal fall are around 28F (-2.2C), and temperatures at or below 28F for an extended period will cause crop loss. Micro-irrigation can increase orchard temperature by a few degrees, with higher flows of water providing a greater warming effect. More on frost mitigation can be found here. With irrigation occurring during multiple frost events, it is common to see trees push slow and with pale green growth. This is due to saturated rootzones that lead to loss of fine feeder roots and low micronutrient uptake. Soil irrigation levels should be monitored, and irrigation withheld until stored soil moisture begins to drop. Furthermore, nitrogen applications should not occur during the period of frost risk as running water for extended periods of time will leach nitrogen out of the rootzone. Crop losses from frost are hard to define in early March. Frost affected flowers will have blackened tissue inside the ovary, or flowers may appear blighted and remain on the tree. Trees will slightly compensate for loss of flowers with a slight increase in fruit set percentage of the remaining flowers as well as greater nut size. Therefore, in areas of minimal damage, the impacts might not be observed. In areas with losses greater than 10%, yield reductions should be expected. If frost damage is suspected, it is important to contact any insurance company as soon as possible and trim the early season fertilizer applications until a better

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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 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 8, 2011Diseases, Nutrient

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

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David Doll2 CommentsMarch 1, 2011Horticulture

Frost Damage in Almonds

Several calls were received today in regards to the symptoms of frost damage. Temperatures in several areas of California were cold enough to cause damage. Many growers have implemented frost protection strategies, but surveying the orchard still needs to occur in order to determine the amount of damage. Damaged blossoms/almonds will be apparent by dead or darkened tissue. Symptoms will become apparent within 72 hours of the frost event, usually appearing 24-48 hours after the event. When viewing the flowers, looked for water soaked areas that might not have yet turned brown. Symptoms will range, but any damage done to the female parts of the flower will most likely lead to flower abortion/loss. Check all parts of the tree, both at eye level and in the upper canopy in order to determine the extent of crop damage. Since frost damage is an abiotic disorder triggered by the environment, keep in mind the following patterns to help discriminate it from other bloom time issues (i.e.Brown Rot):1). Damage is present over a large area of the orchard,2). Damage is present across varieties – especially if both were in the same bloom stage. This may not be true if one variety is yet to bloom and was in the pink tip stage during the event,3). Damage is associated with known topographical changes, i.e. a low spot,4) Tissue of the blossom is darkened, with no obvious signs of fungal growth. The tree’s sensitivity to frost changes with the various bloom stages. The tree is most tolerant to frost when it is dormant or in pink tip. As the tree begins to bloom, it becomes more sensitive to frosts, with the fertilized flowers or small nutlets being the most susceptible. With fertilized embryos, the jacket may protect the ovary/embryo from damage. Here are some pictures of frost damage:

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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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