David Doll1 CommentFebruary 6, 2021Diseases

What is a FRAC group?

 A frequently asked question is “What is a FRAC group?” FRAC is short for “Fungicide Resistance Action Committee”. Simply put, it is a grouping of fungicides based on the mode of action. This numbering system helps users easily identify which type of fungicide chemistry they are using without having to worry about various trade names. It is an excellent tool to help with fungicide rotations to manage and prevent resistance. Fungicide resistance is a numbers game. Fungal pathogens have broad genetic diversity. This means that there is a chance that populations within the same pathogen species may be resistant to the applied fungicide. If this fungicide is applied in successive treatments, this population will continue to infect and spread amongst the host plant. Rotating to different chemistries reduces the risk of these “escapees.” It is important to note that resistance is not due to repeated applications of the same fungicide to the fungal pathogen, but rather that there already exists a resistant population of the pathogen. This resistant population is unaffected by the fungicide because of differences in its genetic code, and will continue to grow unless an alternate fungicide is used. More information on fungicide resistance, which includes some illustrated examples, can be found in this previous article on the Almond Doctor. FRAC groups were established in the early 1980’s. Each fungicide mode of action has a unique code. These codes are updated regularly to consider the changing availability of fungicide chemistries. They include both synthetic, microbial derived, and plant-based fungicides. FRAC numbers are easy to use and the rules are simple. If wanting to reduce fungicide resistance, do not apply the same FRAC group in successive fungicide sprays. By developing fungicide rotation programs, the odds of resistance formation are significantly reduced. This helps keep the fungicide chemistry effective

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Franz Niederholzer3 CommentsFebruary 7, 2014Diseases, Horticulture, Insects

Pollen, Bees, R.U.L.E.S., and Almond Bloom

Almond bloom has begun.  No time of the season is more important to delivering a good crop.  You don’t get a Mulligan at almond bloom.  Good pollinization, delivery of viable pollen grains to the flower stigma of a compatible flower, is the first step of a successful bloom season.  Keeping spray materials off the pollen helps keep the pollen viable for germination (the next step in a good crop) and healthy for bees—the key pollinators from Red Bluff to Bakersfield.

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David Doll0 commentsFebruary 27, 2013Diseases

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?

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David Doll2 CommentsFebruary 15, 2012Diseases

Managing and Preventing Fungicide Resistance

The use of FRAC numbers was created to help determine the mode of action of the varying fungicides. One class of fungicide may have differing active ingredients and be sold under several different trade names. For example, FRAC group 3 is sold as Bumper, Tilt, Elite, Indar, Laredo, and Quash. Regardless of the trade name or active ingredient, any one of these fungicides within a FRAC group kills the fungal pathogen the same way. In order to prevent fungicide resistant pathogens, back-to-back applications of any one FRAC group should be avoided. Figure 1: Application of a fungicide to control a foliar pathogen. The blue dot represents a resistant fungal colony to fungicide A. The formation of fungicide resistance by many pathogens is inevitable as it is basically a game of odds. Making an application of one fungicide kills the majority of the fungi in the environment that are susceptible to that particular fungicide. There are always a few colonies of the targeted fungi that “escape,” and have some degree of resistance to the chemistry (lets say odds of 1/10,000) (Figure 1). This may seem surprising, but this is due to the varying genes found within the same species of fungi (It is no different why you catch a cold, and your coworker remains healthy). Making a second application of the same chemistry provides the environment for the “escaped” population to continue to reproduce and colonize healthy tissues (Figure 2). Eventually, the “escaped” population will become the majority of the population (Figure 3), and attempts to control the pathogen by spraying the same fungicide over and over will not occur (Figure 4A). Figure 2: After fungicide A application, the resistant blue colony “escapes” and begins colonizing other healthy tissues, increasing in population. Employing resistant strategies such as fungicide rotation can delay resistance formation. By avoiding back-to-back

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David Doll0 commentsApril 6, 2011Diseases

Late Scab Timings for Almonds

Early season Scab lesions on almond. We are approaching the end of the effective almond scab control spray timings. Scab has become more common in area orchards due to the increased planting density and occurrence of wet springs. Causing defoliation in late summer, this disease can weaken the tree, reducing crop for the coming years. A heavily infected orchard will have persistent scab issues for several years after the disease flare up. Fritz and Carmel are more susceptible to this disease than Nonpareil and other varieties This spray period starts at about 2 weeks after petal fall and continues to about 5 weeks after petal fall. Years of research by Dr. Jim Adaskaveg and Dr. Brent Holtz have demonstrated that spraying during this period provides the greatest control. The use of strobilurins (FRAC 11 – Gem, Abound, Pristine) provides the greatest control of this disease, followed by the DMIs (FRAC 3 – Quash, Inspire, Inspire Super, Bumper, Tilt), Topsin-M (FRAC 1), and broad spectrums (Captan, Maneb, Ziram, etc). Overwintering scab twig lesions. It is speculated that strobilurin resistant populations of scab are becoming more common. Applying back-to-back applications of strobilurins will hasten the development of resistance. If you sprayed a strobilurin earlier this bloom season you must consider another mode of action for scab control. Earlier entries emphasized the importance of saving this mode of action for summer diseases.  Sprays must be made within the 2 – 5 week petal fall period to provide maximum control. Later sprays will not be as effective. Waiting till the disease is visible before you start to spray is not advise as the population at that point is too high to control. In many cases, spraying at this point will only waste money AND increase the risk of fungicide resistance.  Orchards with severe outbreaks should consider a dormant application of copper/oil to

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