Bloom Spray Additives: Do they work?

Bloom is approaching. Several questions about whether or not bloom spray additives increase flower pollination and set have been asked. I will try and answer them the best I can using information from previous trials across the state. Much of this information is gleaned from Roger Duncan's presentation delivered at the 2010 Stanislaus Almond Day.

Should I include foliar nutrients in the bloom spray?
Several trials from four different advisors from areas across the state (Duncan - Stanislaus, Holtz-Madera, and Edstrom - Colusa, and Viveros - Kern) have indicated that nutrients and other additives included with bloom sprays do not increase yield of almonds in properly maintained orchards. In most trials, yields of the untreated control were higher than the foliar nutrient applied treatment. These were multiple replicated trials held over several years. Materials used can be seen by viewing the presentation linked below.

This trial data can be seen in Roger Duncan's 2010 NSJV Almond Day presentation (click link).

What about Pristine® Fungicide?
Pristine® fungicides is a boscalid/strobilurin mixture that has been used successfully for several foliar fungi that commonly affect almond flowers and leaves (i.e. Brown Rot, Rust, Scab, etc.). There is evidence that suggests that Pristine® causes a yield bump when applied during the bloom or post bloom period. Research by Jim Adascaveg (UC Riverside) and Roger Duncan (UCCE Stanislaus) tested this hypothesis and have not found a significant increase in yield from a bloom or post bloom Pristine® application. It is important to state that in Duncan's trials (Stanislaus Co.), the yields were higher in treatments containing Pristine®, although not statistically significant. Duncan found this same insignificant yield bump when applying Gem®, another strobilurin, in the post-petal fall period.

Conversations with a local consultant indicated mixed success of the Pristine® yield bump across his multi-year trial. Although he did see an increase in yield, this increase was not always significant (significant one year, not significant the next year). The University's results supported his conclusions.

Currently, it is thought that this yield bump may be due to control of fungal diseases at the critical time of nut set/embryo differentiation. This suggests that it may be beneficial to apply a strobilurin during this period. If you plan to apply a strobilurin during bloom or post bloom period, plan to rely on other fungicaide FRAC groups for the other needed fungicide spray timings (Rovral®, Scala®, Bravo®, etc.).

The trial information can be seen in Roger Duncan's 2010 NSJV Almond Day presentation (click link).

It is imporant to keep in mind that there may be situations where these materials may provide a benefit. These may include orchards thathave nutrient deficiencies, high disease incidence, or poor vigor.