David Doll0 commentsMarch 23, 2023Diseases

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

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David Doll6 CommentsFebruary 5, 2022Diseases

2022 Bloom Considerations

Weather is always a consideration when almonds begin to flower. Flowers are one of the most susceptible parts of plants to disease, and environmental conditions that favor disease could lead to crop loss. These conditions include periods of rain and warm temperatures. Protecting these flowers through the conditions is therefore important to maintaining yields and tree health. The forecast at the time of writing for the next few weeks is suggesting dry weather. If dry, warm weather persists, the risk of disease is very low and a different fungicide program should be considered. In this situation, early fungicide treatments can be withheld without too much risk. This is not just due to the dry conditions, but also the warmer temperatures increase the rate in which the tree progresses through bloom. Treatments within this scenario may skip the early and full bloom stages, and focus on an application timed to the petal fall of Nonpareil. If the weather forecast changes and rain is predicted, the plan should change. Rainy conditions over 59F/15C favor brown rot and other spring diseases. If wet, mild conditions persist for over 24 hours, a spray is warranted. This spray should be made prior to the rain event for best coverage. If utilizing FRAC 3, 11, newer 7 fungicides, and 9, this window can extend to 24-48 hours after the rain. Re-application should occur within 10-14 days depending on the frequency and amount of rain received. Fungicides should be applied 30-45 minutes before to provide enough time for them to dry. Although earlier stages of flowering may not require fungicide treatment, an application at petal fall should be considered. This stage of the flower/fruit development is very sensitive to diseases due to the dying flower petals, and amount of dead plant material aggregating within the fruiting clusters.

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David Doll2 CommentsJanuary 29, 2022Diseases

Bloom Sprays: Spray Rig Strategy

Spraying trees during bloom and in the early spring is different than spraying in the summer. This is due to the reduced canopy which allows easier movement of the droplets. Rig speed, therefore, can be increased to help cover the orchard more quickly. Speeds from 3-3.5 mph (4.5-5.5 km/hr) are more common during this period. This contrasts with hull-split sprays which are typically done between 2.0-2.5 mph (3.2-4 km/hr). Many operations have considered every-other-row spray applications during bloom. Although not ideal, this strategy works reasonably well in lower density, small canopied, or young orchards. As the trees increase in size, however, the amount of wood within the canopy increases. This reduces the distribution of spray droplets through the tree, reducing protection on the unsprayed side. Spray rig speed must be moderate (~2.75-3.00 mph) and volume should be high (80-110 gpa, 750-1000 liters/ha) if using this strategy to improve canopy penetration by the droplet. I use this strategy for younger blocks when rain risk is high but uncertain– a spray is made to “side A”, with a follow-up spray made 7 days later to “side B.”  I typically follow up these two “half sprays” with a full spray using a different fungicide chemistry 7 days after the completion of the “B-side.” I only use this strategy for years 3 and 4 (up to 40% canopy coverage). In densely planted orchards, rig speed should be reduced (Figure 1). Increased tree density increases the amount of wood that blocks the distribution of droplets. To compensate, slower speeds must be utilized to improve air displacement and droplet movement. This would also be needed in orchards that have tall trees and have a lot of vertical wood growth. Every-other-row spraying should not be considered in these orchards due to the lack of coverage on the

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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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David Doll0 commentsFebruary 16, 2017Diseases

More Thoughts on Almond Bloom 2017

As forecasted, the weather for bloom 2017 looks wet. This will impact the number of fungicide applications, how we apply the material, orchard access, and bee concerns. This article is a follow up to what was written last week.  Periods of leaf wetness favor fungal pathogen development. Although there are no specific models for blossom pathogens, I general suggest applying a fungicide prior to a rain event in which leaf wetness exceeds 24 hours. This suggests that short, passing storms may not need a fungicide spray, but multi-day storms or multiple passing showers would. With the impending week of wet weather, fungicide applications to reduce the occurrence of disease is strongly encouraged. More on fungicide selection can be found here at the UC IPM website. Fungicides should be re-applied every 7-10 days during periods of heavy rains, and 10-14 days if rain is lighter. This coming storm is a good example of when to apply at closer intervals in which 7 days of rain are expected to drop 3″  within Merced County. Orchard access may be difficult in fine textured soils. This may limit the ability to apply by ground rig. Although aerial application does not provide as effective coverage as a properly calibrated ground rig at bloom, it still is effective in preventing disease. Aerial applications should be considered if field access is limited. I developed a list of aerial applicators and it can be found here. Please note that this is not an endorsement for any company, and if a company was omitted, please let me know so I can update the list. Applications should be completed with enough time to dry. Fungicides need about one hour to be rain-ready.  Many fungicides contain spreaders or stickers. If choosing to add an additional material, please check the UC IPM website for up-to-date bee

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David Doll1 CommentFebruary 29, 2016Diseases

Almond Fungicide Considerations for Upcoming Rain Event

Rain is predicted for later this coming week (Sat through early the following week). This looks to be a multiple day storm with rain potentially falling for 3-4 days. Temperatures will be between 40-60F. These conditions are favorable for a number of post bloom/petal fall diseases, including brown rot, shot-hole, jacket rot (or green fruit rot), anthracnose, and bacterial spot. The almond fungicide efficacy table should be consulted to help with fungicide selection. An updated 2015 Fungicides, Bactericides, and Biologicals for Deciduous Tree Fruit, Nut, Strawberry, and Vine Crops can be found here. Scroll to page 31 to find the efficacy of many common fungicides. Please not that not all fungicides are listed due to the inability to test all trade names. If a fungicide isn’t listed, check to see if the active ingredient is provided, and if not, check the efficacy of the FRAC group. The table on page 32 provides treatment timings which indicate susceptibility of almond to diseases at various growth stages. Finally, page 33 highlights various fungicides that are effective on diseases at specific growth stages and can be used to help determine a rotation. A fungicide product should provide coverage for the above diseases. Products used in earlier fungicide sprays should be rotated to another mode of action (or FRAC group). This should still be considered even if the FRAC number was one part of a combination product.  Rotation helps to preserve fungicide efficacy, which leads to a longer product life (and eventually cheaper prices). Some interesting points to keep in mind when reviewing the tables: FRAC 3 fungicides are not very effective on jacket/green fruit rot; Bacterial spot control will require the use of copper, Manzate Pro-Stick, or combinations of the two products. Keep in mind that almond trees are sensitive to copper. More

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David Doll0 commentsFebruary 25, 2015Diseases

Tank Mixing v/s Pre-Mixed Fungicides

There have been several questions asked by farmers developing their fungicide spray programs for 2015. A repeated question has been: “Is it possible to mix two generic or single mode of action fungicides to create a product similar to the bottle mixed multi-mode of action products?” The short answer: Yes, and often times it is cost-effective because one or both products may be generic. There are, however, more points to consider when determining which strategy is best for the farm operation. Tank-mixing of single mode of action fungicides: Pros: The use of one or two generics in creating the tank mix may help reduce the cost of the overall fungicide application. This, of course, is dependent on the price of both fungicides and the pre-mixed fungicide. Tank-mixed fungicides are usually just as effective as pre-mixed fungicides. A study by Brent Holtz in San Joaquin County has shown that 20 fl oz of Fontelis (FRAC 7) mixed with either 8 fl. oz of propiconazole (FRAC 3) or tebuconazole (FRAC 3) was just as effective in controlling scab as 6.0 fl oz of Luna Experience (FRAC 3/7), 6.0 fl oz of Luna Sensation (FRAC 7/11), or 6.5 fl oz of Merivon (FRAC 7/11). Trials in Colusa County by Dr. Jim Adaskaveg, UC Riverside, showed similar results with 14 fl oz of Fontelis mixed with 8.0 oz of tebuconazole as with 6.0 fl oz of Luna Experience, 5.0 fl oz of Luna Sensation, or 6.5 fl oz of Merivon for controlling almond scab. Selecting multiple single mode of action fungicides provides the flexibility to choose chemistries that work for the disease complex present within the orchard. This may be of more importance in areas that have resistant populations of Scab or Alternaria leaf spot or when trying to manage other diseases that may not be

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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 Doll3 CommentsMarch 6, 2013Diseases

Leaf Wetness is a Fungi’s Best Friend

I always start off most talks about bloom time and spring diseases with the concept of leaf wetness. Although it may seem over-simplified, without leaf wetness (and high humidity), foliar fungi are not able to infect the plant. Periods of leaf wetness are needed for several functions of fungal dispersion and growth. Windy, rainy weather blows spores from infected tissues to new, healthy tissues. Leaf wetness or high humidity provides favorable conditions for spore germination. Once inside the tissues, the pathogen may grow and reproduce faster in wet and mild weather.

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