Preventing spring diseases in almond

Petal fall through the first few weeks of nut development is a critical time for disease management. During this period, the almond fruit, newly emerged leaves, and senescing tissues are susceptible to many diseases. These include jacket rot, anthracnose, brown rot, leaf blight, shot-hole, scab, and with Mediterranean varieties, red blotch. Protecting the developing fruits should be top priority through the early spring. Thorough disease control early in the season prevents the build-up of inoculum, reducing secondary spread of the disease. Typically, this is done with fungicides, which should be applied prior to rain events.  Sprays should be made every 14-15 days if rainy conditions persist, but this period can be extended if dry conditions occur. If using broad spectrum fungicides such as Ziram, Captan, or copper, the re-application interval should be shortened to 10 days in rainy conditions. The appropriate chemistry should be chosen to target the disease of concern. For example, triazole (FRAC 3) and strobilurin (FRAC 11) fungicides are not effective on botrytis jacket rot, but they do control other diseases well.  Additionally, fungicide chemistries, not commercial brand names, should be rotated to reduce the formation of resistance. This is because multiple commercial brand names may use the same fungicide chemistry. This process has been streamlined through the use of a FRAC number. This number indicates the mode of action of the fungicide, and use of the same number in back-to-back applications should be avoided. There has been increasing interest in biological products for control of diseases within almonds. Generally, these products work well in mild-to-moderate disease pressure years, control tends to be reduced in high pressure years(i.e. prolonged wet, rainy conditions). Some of these products can be tanked mixed with fungicides, but others cant. If the product is a live agent, such as a bacteria or

Read More

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

Read More