David Doll2 CommentsFebruary 12, 2023Horticulture

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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David Doll4 CommentsFebruary 9, 2020Diseases, Horticulture

2020 Bloom Considerations

As the 2020 almond bloom/crop year begins, there are several considerations to keep in mind. These points may be useful to help understand observations from the field as well as provide an understanding of any direction received. Nut set. Flower set percentages will vary from year-to-year. For mature trees, about 20-30% of the flowers will set while younger trees will be slightly higher. Even though this is low, crop loads are still high due to the number of flowers that are in each tree. A mature tree will have an estimated 35,000-50,000 flowers, depending on tree size. For more information on this, please see this article: https://thealmonddoctor.com/2016/03/07/almond-set-and-nut-drop/ which discusses the results of a tagging study which followed the development of almonds through the season. External factors greatly influence the set percentages. Crop load from the previous year impacts the amount of energy available for flower formation and bloom. High yields from the year before will reduce the number of flowers that will set nuts. Poor weather conditions can reduce bee flight hours, kill flowers in freezing temperatures, or promote disease. The period of weather risk extends into the fertilization period, which continues for several weeks. Keep in mind that the crop is susceptible to frost and diseases as long as there is a risk of frost and rainfall.   Several factors can be mediated by good farming practices. These include the presence and strength of pollinators (usually honeybees), post-harvest practices, and nutrient deficiencies. Honeybees are required for varieties needing cross pollination (most CA orchards – 2.0-2.5 hives/acre) and recommended for self-compatible varieties (0.5-1.0 hive/acre, although the exact number is unclear). Stronger hives (8+ filled frames) are essentially an insurance policy for poor weather conditions. Hive numbers and placements should take into account the weather. Post-harvest treatment of the trees is

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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 Doll8 CommentsFebruary 15, 2016Horticulture

2016 Almond Bloom Considerations

Adequate chill and recent warm temperatures have accelerated almond bloom. Timing is close to “normal” in southern and southwestern areas of the State, but are 1-3 weeks ahead further north. Below are some thoughts to keep in mind with the anticipation of rain this week. Authors note (2-16-2015): There has been some concern about the wording around the time of nutrient/boron sprays and bloom. Research has shown that boron applied postharvest to 10% bloom can increase yield, while applied later than 10% bloom will not have an impact. Nutrient sprays-with the exception of boron as described in the previous sentence- have not been found by researchers to increase yield when applied at bloom. Sorry for the confusion. Fungicides are usually effective for about 14 days after an application. This period of protection is decreased with rain events. Furthermore, as surface areas expands – whether it is the flowers or leaves – newly exposed tissues are unprotected from infection. This means that spraying too early may not provide the wanted protection. If planning to make a fungicide application, apply the material as close to the rain event as possible. Remember that it needs between 30-60 minutes to dry. Depending on the pre- and post-rain conditions, and the periods of leaf wetness, a fungicide spray may not be needed. Keep in mind that fungal diseases require several hour periods of leaf wetness – which comes from fog, dew, and rain. Be cautious with adding additional surfactants. Most fungicides have surfactants mixed with the active ingredient. Adding additional surfactants may impact the efficacy of the fungicide, damage the flower’s tender tissues, or impact bees. The label should indicate if a surfactant is needed. Avoid tank mixing in boric acid with sprays made during bloom when bees are active(1). Researchers at the University of California as well as around

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David Doll6 CommentsFebruary 17, 2015Horticulture, Irrigation

More Leaves than Flowers: Why?

I have received a few reports about poor bloom conditions on ‘Nonpareil.’ In these cases, flower density appears to be low and leaves are starting to push (See Figure 1) indicating that the fruit buds did not develop over the past year. From the reports, trees tend to be between the ages of 6 and 12 years old and have been observed across Merced County. A number of issues may be responsible, including the following: Water stress. Reductions in water resources over the past year have led to reduce vegetative growth in many orchards. This lack of growth prevents the formation of vegetative buds (in-season) which develop into fruit bud (post-harvest through dormant period). Research has shown that spurs that remain in good light positions tend to “take a year off” after bearing fruit, while others receiving too much shade die. Therefore, canopy growth must be maintained to some extent to keep crop loads high. Salinity Induced Water Stress. Increasing soil salinity decreases the osmotic potential of the soil, making the plant “work harder” for water. This leads to water stress and reduces the energy diverted into vegetative growth and floral bud development. High yields over the past few years. Trees producing large yields in successive years have been observed to have an “off year.” This is due to most of the plants energy being diverted into the crop load, reducing the amount available for developing new fruiting spur positions. As discussed earlier, if this happens in successive years, the number of viable fruit spurs may be reduced leading to a reduced crop. Re-leafing in the Fall after leaf drop from foliar disease, salt, or mites. Bloom density would be lower if the tree defoliated last summer or fall from lack of water, too high of salt levels, foliar disease,

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David Doll0 commentsFebruary 27, 2013Diseases

No Rain at Bloom – Some Q&A

Looking at the 12 day forecast, it looks like it is going to be a dry couple of weeks for the San Joaquin valley. Although this may be a benefit for the almond crop as good weather favors pollination by bees (and we were short on bees in 2013), we do need the rain/snow. With sunny and 70 degree days, I have received a few questions regarding fungicide sprays. Q: Do I need to spray for brown rot, shot-hole, and jacket rot?

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David Doll4 CommentsFebruary 24, 2012Horticulture

Some Thoughts on 2012 Bloom

To date, the weather has been very warm, with conditions favoring bee flight and pollination, but not the various bloom time diseases. The bloom looks strong across the county. In other words – so far, so good. I have received a few calls from a variety of topics, and will post some thoughts on these topics. Next week, there looks to be a few showers moving into the area, so fungicide coverage may be needed to prevent various diseases – especially if a fungicide application hasn’t been made. If an application has been made, it should provide protection for 10-14 days, dependent upon the amount of rain received. Delayed Varietal Bloom, Weak Bloom.I have received several calls regarding delayed bloom of Monterrey and Fritz. Although these thoughts are conjecture, discussions with a few advisors concluded that post-harvest tree conditions/ practices may be the cause for these issues. Tree conditions include defoliation of trees last fall from scab and rust, water stressed from a delayed harvest, and inadequate rainfall during the dormant period. Practices that may have encouraged this separation include delayed application of nitrogen and water during the post-harvest period, and missed pre-irrigations this past winter due to lack of water. Also consider that these trees have had high yields over the past few years – with two years of delayed harvests (mid-Sep-Oct) with Fritz/Monterrey. Many people have asked about inadequate chilling being a possible cause, but ample chilling has been received. More importantly, if it was a weather effect, we would expect to see the variations in bloom time occurring across a wide area – not just in a single orchard. For example, one orchard has had an issue with the delayed bloom, while the neighboring orchard with the same varieties is blooming as expected. Birds Eating Blossoms?Catching me a bit

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David Doll3 CommentsFebruary 9, 2012Diseases

Bloom Time Diseases and Control

Almond orchards are usually treated once or more during bloom for prevention of fungal diseases. These diseases include Brown Rot, Jacket Rot, Shot-hole, and Anthracnose. Flowers, flower parts, and young nuts are susceptible to infection, and often serve as the primary point infection for these diseases. Lack of properly timed sprays can provide the opportunity for a large amount of Brown rot infection of an almondblossom. The grey “fuzz” is the sporesproduced by the fungus.   infections. These epidemics create lingering disease issues which will cause orchard loss for the present and future cropping years. Brown rot, Monilinia laxa, infects the petals, pistils, and stamens of the almond flower. Upon infection, it moves into the woodier tissues of the tree, killing branches and forming cankers. All varieties are susceptible to brown rot, but they vary in their degree of susceptibility. Butte, Mission, and Wood Colony are the most susceptible; Carmel, Sonora, Fritz, and Monterey are moderately susceptible, while Aldrich, Nonpareil, and Peerless are the least susceptible. Brown Rot Blossom blight is usually controlled with a pink bud and full bloom treatments. Many of UCCE trials indicate that the full bloom treatment is the most important. A third petal fall spray may be necessary in years favorable to disease, especially if bloom is strung out and the weather is wet and rainy. A good rule to follow is that no more than ten days should elapse between treatments in wet weather. Canker caused by brown rot within Butte. This canker serves as a restingstructure for the fungus. A few growers have indicated that they do not spray for brown rot. This may be possible if good conditions persist through bloom AND the varieties planted are not very susceptible to infection (i.e. Nonpareil). It is important to note that not spraying can lead

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