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 (even self-fertile varieties seem to benefit from bees!). Do not mix insecticides with bloom sprays, and check the label of the fungicide to determine if additional surfactants are needed.
Fungicide sprays ideally should occur at a time to reduce bee exposure. This is generally in the afternoon and into the night. Also, hive strength should be monitored to make sure the contracts are being fulfilled.
Keep track of temperature. Warm temperatures during bloom will accelerate progress, which may mean spray schedules may need to be changed. Cooler or mild temperatures have the opposite effect. Temperatures below freezing are concerning as it may kill flowers. As buds progress through the flowering stages, they become more sensitive to cold. Nights with temperatures below 28-29 degrees should utilize the irrigation system to increase orchard heat. Utilize in-field temperature sensors as orchards may be cooler than reported temperatures in the urban areas. Only frost protect when needed as too much water at this time can saturated the soils, impacting tree health. If unable to frost protect all the acres at night, consider providing soil moisture during the day or run every-other row to stretch the water.
For further asistance on bloom time considerations, remember to review the Fungicide Efficacy tables provided at the UC IPM website as well as "Growing the Valley" podcasts posted by Phoebe Gordon (UCCE Madera) and Luke Milliron (UCCE Butte).