Prioritizing Bloomtime Applications In Almonds

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Worst case scenario: I was just getting ready to apply a pink bud spray to my almonds which included a fungicide, some nutritional sprays, and a “plant-health” yield enhancer. Then the wind started to blow so I had to wait. Soon the blossoms were 50% open so I had to pull out the boron and soluble NPK mixes. I got set to spray again, then the rains came. By the time I could access the ground, the wind started blowing again and I was at full bloom.

By the time the aerial applicator I had to call was available, I had revised my decision on the choice of fungicide due to the change in disease spectrum timing, revised the nutrient list due to pollination concerns, and also planned to add an insect growth regulator (IGR) for peach twig borer control. When I realized the pH of the nutrients I had switched to was undesirable for the fungicide and IGR, I again changed my choice of materials.

As I was planning to order materials, I discovered the material I had switched to did not have an aerial label so I had to change my material choice again. Since it was starting to approach petal fall, I changed my choice of IGR but realized it would require two applications about a week apart. So I changed that, not wanting to make the second application. I then changed my choice of fungicides again since the “plant-health” aspects of a certain material I was interested in better fit my timing.

The problem now was that I was planning to use a product from the same chemistry group for scab, rust, and alternaria management in May, and this would result in a back-to-back treatment with a similar product group which is bad for resistance management. I also wanted to combine a phosphite-based material and calcium with this petal fall fungicide, but realized the mix was incompatible and would, without visual evidence, neutralize the phosphite to ineffective phosphate. I had to re-order a compatible calcium or my money would be wasted on the phosphite.

Tough Decisions

Welcome to farming. Obviously this story is hypothetical, but it probably hits close to home for many. The almond bloom period of 2009 presented some major challenges for growers trying to apply bloomtime sprays, be it a fungicide, a nutrient, or a plant health modifier. Dealing with the wind and rain is not new for growers, but each year there is new information or new products available that present more choices and more management decisions as to when is the best time to apply them.

The pink bud timing is usually the first point at which a treatment is considered. Nowadays it is rare that a single product is applied, since growers are looking for ways to reduce costs by “piggy-backing” combinations of materials to save on application costs. This creates numerous considerations including efficacy, compatibility, or even negative interactions resulting in phytotoxicity or lack of performance of key ingredients.

Once the decision is made on the product, then the question is the best time to treat. Usually, Nonpareil is at lower risk compared to most pollenizers. If the treatment is delayed until the optimum opening of the pollenizer, then are there too many Nonpareil flowers open to consider applying certain foliar nutrients like boron or highly soluble NPK mixes? If you pull out the nutrient, do the benefits from it outweigh the risks associated with it? This depends on the individual situation.

With boron, there is research to show the negative effects on pollination associated with applying it to fully open blossoms. However, in acutely deficient areas such as light sands, keeping boron levels high enough is difficult without multiple applications. The postharvest period and the pink bud period have been the two most efficacious timings for boron applications. If chronically low boron is affecting production, then a slightly late pink bud timing will probably outweigh the risks of suppressing pollination with the boron. If trees are at full bloom, until there is more information available, it is probably best not to include the boron. This brings up the issue of alternate timings. A pre-leaf drop postharvest boron application or soil treatments are some alternatives that will reduce the need for bloomtime boron.

Wes Asai is a former University of California farm adviser and is currently owner of Wes Asai Pomology Consulting in Turlock, CA.

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