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 the world have not found an increase in yield with boron applications made at full bloom (1). Furthermore, boric acid is a known insecticide, and can impact bees.
- Be careful with bees. Do not tank mix in any insecticides for PTB besides Bt. Pesticides applied at this time do not control Navel Orangeworm. Do what is possible to reduce pollinator exposure to pesticides. More on this topic can be found here.
- Although nobody believes it, several replicated research plots testing foliar nutrition applications at full bloom have not shown an increase in yield. These trials were in Kern, Stanislaus, and Colusa County. Granted, not all of the products on the market have been tested (there are only several 100), but nearly all of them have a high mark-up. Feel free to tank-mix in what you want, but consider asking questions regarding what you are applying and why.
- Do not irrigate too early. Nutrient uptake at this time of the year is minimal, but the ability to kill roots from saturated soil is great. If the tree was fertilized in the post-harvest, it should have enough nitrogen stores to make it through bloom and into full leaf-out. Killing roots now will lead to increased stress levels in June/July.
- Never-the-less, don’t ignore the irrigation system altogether. Make sure to perform the required maintenance in case it is needed for frost protection.
(1) – Edit to clarify the timing of boric acid application made on 2/15/2016.