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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2023 Bloom Considerations

The weather during almond bloom can vary from day-to-day. This creates challenges with farm operations, but also changes how the tree adapts to the weather. Cooler, hotter, or wet weather has significant impacts on the pollination process, fertilization of the ovule, and eventual crop set. Cooler temperatures aren’t necessarily bad for bloom. Flower development is growing degree day based, meaning that cooler temperatures will slow flower development. Additionally, the viability of the ovule and pollen are longer when temperatures are cooler. This natural response increases the pollination period, and partially explains why crop set is often larger than expected during cooler than desired bloom periods. A video presentation on almond pollination and fertilization can be found here. Cooler temperatures, however, do impact honeybee activity. Temperatures below 55F (12C) suppress honeybee activity as more bees are required to remain in the hive to keep it warm. This means fewer bees are available to gather pollen and nectar, affecting the rate of the pollination process. If hive temperatures drop too much, the rate of the queen’s egg laying decreases, affecting eventual hive strength. This could be problematic during extended periods of cold temperatures followed by warm temperatures with a fast/short bloom. The effect of cold temperatures on honeybee activity is why strong hives (8 frames or more) are recommended. Hives with more frames of bees have more bees, which means hive temperatures are higher and more bees can forage. This is often evident on cold mornings, when hive inspections can reveal lower bee activity in weaker hives. If temperatures are too hot, the bloom period can be rapid. In high temperature years, bloom can finish in 7-10 days. High temperatures also shorten the viability of pollen and the ovule. Bee foraging activity must be able to match the rate of flower opening

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Flooding and Almond Tree Survival

When periods of high amounts of rain occur, orchards can become saturated and flooded. During these periods, tree loss may occur, but this is dependent on the duration of soil saturation, the timing of year, and rootstock. Soil saturation reduces the ability for oxygen to infiltrate into the rootzone. Roots require oxygen to respire, and long periods of saturation can lead to root loss by asphyxiation. Fine feeder roots are often the first affected, with larger secondary roots affected during periods of extended saturation or flooding. Tree survival is dependent on how many roots survive and can regrow before periods of high transpiration occur. The sensitivity of almond roots to saturation is dependent on the timing and duration of the flood event. During dormancy, trees are reasonably tolerant due to lower soil temperatures and low rates of respiration. Flood events that are shorter than 7 days will not have any affect on tree performance. Extending beyond this, however, some root loss will occur, and poor spring tree growth may occur. With extended periods – beyond 10 days – tree loss may occur. After the trees have leafed out, the period of tolerance is much shorter. Standing water within an orchard for 5 days will kill mature trees. This is due to the higher activity of the root system due to warmer soil temperatures, and overall tree activity. In these cases, efforts to drain as much water as possible should occur to reduce the impact of the flooding event. If water is moving through an almond orchard, the effect of soil saturation/flooding is reduced. Since moving water carries oxygen, some movement of oxygen into the soil can occur. This will extend the period before negative impacts are seen by several days. For example, an orchard near the Merced River was flooded

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Reduced Kernel Size – 2021 Harvest

There have been several reports of smaller than expected nut size for the 2021 harvest. Nonpareil sizes have been reported to be in the range of 28-30/ounce rather than the typical 24/25 nuts per ounce. Many have suggested that this is due to drought induced water shortages, but this has occurred even on fully irrigated orchards. Water stress has played a role, but earlier conditions of the season should also be considered. Nut weight is influenced by a few different factors. These include: Reduced number of cells; Reduced cell size; Reduced cell weight. Cell number is mostly impacted by temperatures that occur during cell division, which occurs early in the season, typically within 6-8 weeks following fertilization. Cell enlargement is influenced by plant stress. It begins in April and continues through May. Lastly, weight accumulation begins in May and continues until early August. It is influenced by plant stress, which reduces the production of carbohydrates. To maximize nut size, carbohydrates (sugars) must be available during these periods for cell building processes. Carbohydrate availability is influenced by the rates of photosynthesis and respiration. These two processes are heavily influenced by plant temperature, which are influenced by ambient air temperature and water availability. Temperature influences photosynthesis and respiration. Both processes increase rapidly as temperatures warm, and begin to drop as temperatures increase above a certain point. The peaks, however, are different, with 86F and 103F for photosynthesis and respiration, respectively (figure 1). Since these peaks are different, there is a net gain of carbohydrates when temperatures are below 86F, but a net loss as temperatures increase above this point. Furthermore, as temperatures warm towards 86F, there is more energy being directed towards respiration, which reduces availability to be used for other processes, like nut development and plant growth. Internal plant temperature is

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Drought and Almonds: Spring Considerations

The current drought conditions faced by California will impact the agricultural industry. Annual precipitation, snowpack, and reservoir conditions are well below average for this time of the year. Although there is some rain in the forecast, future rain and snowfall amounts are hard to predict. Furthermore, spring storms tend to come in warmer temperatures, leading to more rain but less snow at lower elevations. Although we cannot control the weather, there are things we can do to improve the use of water resources. These practices will improve the use efficiency of on-farm water resources. They also include strategies to help capture more water from spring rain events. Lastly, implementing practices now will provide on-farm data for future mitigation strategies as the Sustainable Groundwater Management Act (SGMA) comes into full enforcement. Start timing. Most farm operations begin to irrigate too early. This occurs even in low rainfall years. Stem water potential (SWP) or other plant-based monitoring systems are strongly recommended to help determine start timings in the spring. With SWP, recommendations are to wait to at least 2 bars more negative than baseline (remember, SWP is read in negative numbers). This will most likely lead to an irrigation timing around early- to mid-April, depending on leaf-out date. A study demonstrating this method was established in a ‘Butte’/’Padre’ located near Delhi, CA in a very sandy soil. The trial was established in the drought year of 2014-2015 and continued through 2017. Within this study, the delayed start to the irrigation did not impact yield in comparison to the grower standard. The dates for the first irrigation were between April 22nd – 26th, for all three years. Since ‘Butte’ and ‘Padre’ are later leafing cultivars, I suspect that ‘Nonpareil’ and other earlier leafing cultivars will be 1-2 weeks earlier. This delay saved between

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Tracking Winter Chill in Fruit Growing Regions

Written by Franz Niederholzer1 and Kitren Glozer2 1UC Farm Advisor, Sutter/Yuba Counties, 2Associate Project Scientist, Department of Plant Sciences, UC Davis “Is it a good chilling year?”  That’s a common coffee house question this time of year in fruit and nut growing regions.  The amount of chilling a perennial crop accumulates in a given winter will influence bloom conditions – the most crucial time in a crop season.  Less chilling than a certain tree crop requires can lead to an extended bloom; too little altogether can result in bud death and drop in some crops like apricot and sweet cherry.  ‘Good chilling’ (more chilling than the minimum required) can produce a very short bloom season, or ‘snowball bloom’.  Chilling models can provide growers and their advisors with key information to time dormancy-breaking materials (hydrogen cyanamide, oil, etc.) to manipulate bloom to improve or maintain yield and quality in regions where local chilling is marginal for a certain crop.  Climate change may make achieving critical chilling more important in years to come.  In this article, we’ll briefly review chilling and chilling models.  Deciduous perennial crops break bud in the late winter or spring after a certain amount of cold weather (chilling) followed by a certain amount of warmer weather.  Think of this process as a relay race.  The chilling is the first leg of the race, and the heat accumulation is the second leg.  Bud break is the finish line.  The length of each leg of the race depends on crop and variety.  The weather during the race influences the runner’s speed.  Good chilling weather speeds up the chilling leg, warmer weather can slow it down or even stop it.  Cool weather on the warming leg slows the progress towards bloom.  Since most perennial crops are not native to North America,

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Factors to Consider when Determining Honeybee Hive Needs for Almond Orchards

Determining the number of hives to rent for an almond orchard can be challenging. With a strong reliance on honeybees for pollination, placing too low of number of hives and bees can reduce crop potential, especially in inclement weather, while placing too many increases operational expenses. To determine the proper hive strength for the almond orchard, the following factors should be considered: Varieties present within the orchard Age of the orchard Strength of the hives contracted Crop insurance requirements Anticipated weather for the orchard’s production area; Presence of other pollinators. Almond Varieties within the orchard. All almond varieties benefit from having pollinators present during bloom. In California and Australia, the primary varieties planted are ‘Nonpareil’ and the selected compatible, pollinating varieties. Since these varieties, as well as others (e.g.’Butte’/’Padre’), require cross-pollination to set a nut, bees are required to maximize orchard yields. Due to the requirement for cross-pollination, the recommendation by the University of California has been to place two 6-8 frame hives per acre (5 hives per ha) to maximize pollination (Micke, 1996). In Europe and more recently in California and Australia, self-pollinating almond varieties are present. These varieties do not require pollen from a compatible variety to fertilize the flower. In these orchards, bees are not required to set a commercial crop, but they have shown to increase yields. In Europe, studies have shown yield increases between 5-20% amongst European varieties. In California, the presence of honeybees has shown to increase yield by 20% or more within ‘Independence’ (Saez, et al, 2020).  These studies indicate that bees should be placed to optimize pollination, but suggest that the number of hives per acre can be fewer. In Europe, 1-1.25 hives/acre (2-3 hives/ha) are common stocking rates within orchards that utilize bees. This may be a reasonable range to consider

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