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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Flooding and Almond Tree Survival

When periods of high amounts of rain occur, orchards can become saturated and flooded. During these periods, tree loss may occur, but this is dependent on the duration of soil saturation, the timing of year, and rootstock. Soil saturation reduces the ability for oxygen to infiltrate into the rootzone. Roots require oxygen to respire, and long periods of saturation can lead to root loss by asphyxiation. Fine feeder roots are often the first affected, with larger secondary roots affected during periods of extended saturation or flooding. Tree survival is dependent on how many roots survive and can regrow before periods of high transpiration occur. The sensitivity of almond roots to saturation is dependent on the timing and duration of the flood event. During dormancy, trees are reasonably tolerant due to lower soil temperatures and low rates of respiration. Flood events that are shorter than 7 days will not have any affect on tree performance. Extending beyond this, however, some root loss will occur, and poor spring tree growth may occur. With extended periods – beyond 10 days – tree loss may occur. After the trees have leafed out, the period of tolerance is much shorter. Standing water within an orchard for 5 days will kill mature trees. This is due to the higher activity of the root system due to warmer soil temperatures, and overall tree activity. In these cases, efforts to drain as much water as possible should occur to reduce the impact of the flooding event. If water is moving through an almond orchard, the effect of soil saturation/flooding is reduced. Since moving water carries oxygen, some movement of oxygen into the soil can occur. This will extend the period before negative impacts are seen by several days. For example, an orchard near the Merced River was flooded

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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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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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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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Almond Fungicides and Bloom: Plan Your Work, Work Your Plan

Planning your fungicide program has multiple benefits, and now is a good time to start doing so. Time can be taken to identify fungicides and respective modes of action to develop a proper rotation strategy. It allows the ability to price and compare differing options that may swap materials at specific points. Finally, it gives the opportunity to review the labels of the materials to determine application requirements, and the need to include (or most likely exclude) additional materials. To determine the year’s spray program, several things need to be considered. These include anticipated weather during flowering, disease history, materials available, operational tolerance to disease, and the ability to spray (budget constraints). Dry weather during flowering will reduce the need to spray, while free moisture from rainfall or humidity/fog can increase disease pressure. If dry conditions are present, fungicide sprays can be withheld until conditions change. In these types of years, bloom typically progresses rapidly, making it difficult to spray due to the shorter duration. As the flowering period ends and petal fall begins, it may make sense to consider a “clean-up” spray for any infections that might have occurred. Having a history of disease increases the presence of the given disease’s inoculum. This means that as soon as any rain event occurs, this disease will begin to spread at a higher rate. If dealing with a previous outbreak of a disease, especially diseases that form wood cankers (e.g. Anthracnose, Monolinia, Phomopsis, etc), fungicide applications should occur prior to going into any wet period, and re-application should be considered for any rain events that occur 10-14 days after the previous application. This may mean multiple sprays during wet years to reduce disease inoculum. As incidence decreases in future years, the spray program can be gradually reduced. Available chemistries for disease

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Shot Hole Fungus on Almond

Shot Hole is a fungal disease caused by Wilsonomyces carpophilus. The disease is able to infect leaves, fruits, and green wood. Leaf infections are characterized by a lesion that is between 1/8″-1/4″ (3-6 mm) in diameter, with a definitive yellow halo. Often, the lesion has a small black fruiting body in the center. As temperatures warm, the lesion drops from the leaf, leaving a hole. Fruit infections are generally smaller in diameter (~1/8″), appearing purplish-brown, slightly cork-like in appearance, and are raised. Severe fruit infections can kill the developing nut or cause deformities, impacting quality. Twig infections are similar to fruit infections. In severe cases, multiple lesions may girdle the green branch, causing dieback. This disease is very common in almond producing areas around the world. It survives/overwinters on infected twigs and as spores within leaf buds. Infection occurs when there is ample moisture and temperatures above 36F/2C. In warmer conditions, the fungus can produce spores and infect leaf tissues in less than 6 hours. Multiple infection cycles can occur within a season due to re-occurring rain events, which can cause severe defoliation. Due to the requirement for leaf wetness, this disease tends to be more prevalent in production areas that have significant rainfall after leaf-out. Frequent periods of leaf wetness that are greater than 6 hours will increase the risk of disease. In order to prevent infections, fungicides should be applied prior to rain events. These products kill the spores as they begin to germinate, reducing the number of infections. If rainy periods persist, multiple fungicide sprays will be needed. For more information on control, please see the Univ. of California Integrated Pest Management website. It highlights the life-cycle and fungicide chemistries to utilize for control. When diagnosing, be aware that there are a lot of problems that look

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Glyphosate Drift on Almond

Glyphosate is a very effective herbicide due to the stability of the chemical once it enters the plant. Off-target drift of this herbicide onto almond, however, can cause reduced, stunted growth, and if in high enough concentrations, tree death. Drift symptoms are usually very obvious and appear similar to severe zinc deficiency. In some cases, the only way to determine the possible cause is to make a foliar application of zinc – if the symptoms are alleviated, it was a deficiency. If not, the damage was from glyphosate. After the appearance of the symptoms, it could take 2-3 months for the tree to begin to grow normally. Applying glyphosate at any time of the year can injure the tree, including dormancy. Therefore, care must be taken to reduce drift and the subsequent effects by using properly calibrated spray equipment, drift reducing surfactants, and reduced winds at the timing of application. The pictures below show the effects of dormant applied glyphosate drift onto almond 2 months after the application. The second photo shows the recovery of the limb and was made 10 weeks after the herbicide application. Once drift damage occurs, there is nothing that can be done besides to wait for recovery. Applying foliar nutrients does not expedite recovery. This has been demonstrated in multiple field demonstrations and trials. Prevention is the best cure.

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2020 Bloom Considerations

As the 2020 almond bloom/crop year begins, there are several considerations to keep in mind. These points may be useful to help understand observations from the field as well as provide an understanding of any direction received. Nut set. Flower set percentages will vary from year-to-year. For mature trees, about 20-30% of the flowers will set while younger trees will be slightly higher. Even though this is low, crop loads are still high due to the number of flowers that are in each tree. A mature tree will have an estimated 35,000-50,000 flowers, depending on tree size. For more information on this, please see this article: https://thealmonddoctor.com/2016/03/07/almond-set-and-nut-drop/ which discusses the results of a tagging study which followed the development of almonds through the season. External factors greatly influence the set percentages. Crop load from the previous year impacts the amount of energy available for flower formation and bloom. High yields from the year before will reduce the number of flowers that will set nuts. Poor weather conditions can reduce bee flight hours, kill flowers in freezing temperatures, or promote disease. The period of weather risk extends into the fertilization period, which continues for several weeks. Keep in mind that the crop is susceptible to frost and diseases as long as there is a risk of frost and rainfall.   Several factors can be mediated by good farming practices. These include the presence and strength of pollinators (usually honeybees), post-harvest practices, and nutrient deficiencies. Honeybees are required for varieties needing cross pollination (most CA orchards – 2.0-2.5 hives/acre) and recommended for self-compatible varieties (0.5-1.0 hive/acre, although the exact number is unclear). Stronger hives (8+ filled frames) are essentially an insurance policy for poor weather conditions. Hive numbers and placements should take into account the weather. Post-harvest treatment of the trees is

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