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?

A. Since the blossoms are the most susceptible to fungal infection, they are easily infected by these three pathogens. Some varieties, such as Nonpareil and Aldrich, are more tolerant to infections and can often go without sprays in years of dry weather (or even light rain). Other varieties are more sensitive (i.e. Butte, Wood Colony, Padre), and can have severe blossom blast in no-rain years.  These sensitive varieties will need to be covered with a fungicide regardless of conditions as the morning dew provide enough moisture for infection.

Q. What about the other varieties?

A. Based on Dr. Jim Adaskaveg’s assessment of brown rot and shot-hole, most of the other varieties (Monterey, Sonora, Fritz, and Carmel) are moderately susceptible to these diseases. Based on those observations and taking a conservative approach, a spray should be applied, and a single spray at full bloom should provide enough protection in a no rain year.

Q. What fungicides should we consider for this full bloom spray?

A. Even with the concerns of some fungicides in regards to bee health, there are a lot of other available chemistries. I would look to choose a chemistry that is effective on brown rot, shot-hole, and jacket rot, but not a chemistry that is planned to be used for later spring treatments for scab, rust. Some products that fit this niche include Vanguard/Scala (FRAC 9), and Elevate (FRAC 17). Using one of these products will provide the ability to come back with either a DMI (Frac 3) or strobilurin (FRAC 11) later in the season.

Q. That sounds good and all, but propiconazole (FRAC 3) is so cheap!

A. I cant argue with that. If planning to apply a DMI at full bloom, I would advise to rotate away to another chemistry for the 2-5 week post petal fall spray. Broad spectrum or multi-site chemistries are a good fit for this time period. Products to consider is chlorothalonil (FRAC M5), Captan (FRAC M4), Maneb (FRAC M3), Ph-D (FRAC 19), Syllit (FRAC M7) or Ziram (FRAC M3). Using a broad spectrum will allow a rotation away from the DMI group, providing the option for a re-application later in the season of a stand-alone DMI or DMI/Strobilurin (or other chemistry) mixed product. Be awar that there are possible phytotoxic issues with applications of oil (May spray) too soon after some of these fungicides.

DMIs are not as effective as other chemistries on jacket rot/green fruit rot.

Remember- DMIs are becoming cheap because the patents are beginning to expire and generics are being released. Overuse of these products will lead to resistance, which will make the cheap products ineffective. Only by rotating FRAC groups can we prevent this from occurring. 

More information regarding fungicide efficacy and timings can be found here.

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