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 Doll12 CommentsJanuary 16, 2021Diseases

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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David Doll0 commentsApril 17, 2020Diseases

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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David Doll8 CommentsSeptember 29, 2019Diseases

Phytophthora: An Update

As previously written (2009 article and 2015 article), Phytophthora is a plant pathogen of almond trees. This fungal-like water mold is common throughout the various almond growing regions of the world, with 6* or more known species causing disease. When conditions are conducive for infection, the pathogen directly invades plant tissues at the crown or roots, leading to loss of nutrient and water uptake, causing tree decline and eventual death. The rate of infection and tree loss depends on the inoculum present, the choice of rootstock, environmental conditions, and cultural practices that may favor disease. Phytophthora inoculum can be endemic to the orchard area or introduced through a variety of ways. Low levels of Phytophthora probably exist in most soils, but typically are not at the levels or location to cause infection unless there are prolonged conditions favoring disease.  Generally, introduction of inoculum into the area of close proximity to the plant is most likely responsible for infections and tree death. This includes the crown or base of the tree where the pathogen infects the plant just below the surface of the soil. These types of infections are most common and can lead to rapid tree loss.  Root infections, which occur when soils are saturated with water, lead to a gradual decline. Finally, aerial Phytophthora happens when spores are deposited on limbs or in crotches of the trees through dust or flooding, followed by wet conditions (e.g. rain). Surface water is believed to be the major contributor of Phytophthora inoculum in perennial nut orchards. Surveys have found several species of pathogenic Phytophthora in high elevation, upstream waterways of the major rivers in California. Due to the ability of the pathogen to survive in water, this pathogen is probably found in all surface water used to irrigate trees worldwide.  This inoculum

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David Doll0 commentsAugust 8, 2019Diseases, Field Notes

Field Note – Powdery Mildew of Almond

Written by Cameron Zuber, UCCE Merced County Some interesting almonds came into the office and, no, this is not a setup for a joke. In the middle of July, some almond fruit nuts from Le Grand, CA were brought into the Merced County UC Cooperative Extension office. There were various signs of possible pest damage and disease infection. These included black growth inside the hull indicating possible Rhizopus stolonifera fungus which may lead to hull rot; grayish-black spots indicating scab (Cladosporium carpophilum); and gumming which may indicate bacterial spot (Xanthomonas arboricola pv. Pruni), anthracnose (Colletotrichum gloeosporioides), or bug feeding. However, the greatest amount of damage were odd areas of russeting and cracking on the hull. After speaking with person who brought in the samples, there was not any indication of leaf or shoot die back near the nuts which starts to rule out hull rot and lab tests did not show any fungi that would cause hull rot. Lab test also showed some instances of almond scab growths, but none of these pest or disease symptoms were at a level to be extremely concerned about. Also, none have been shown to cause the odd cracking on the hull, so what was the cause, should you be worried about it, and how do you fix it? The cause was found through some digging and a lot of help from farm advisors and plant pathologists. It was determined that the cause was most likely a false powdery mildew (or powdery mildew-like) fungus of the Acremonium species. Normally these organisms live on dead or decaying organic matter (i.e., saprophytes), but do occasionally infect plant material and, for almonds, result in the russeting and cracking seen in the above fruit nuts. It is called “false” or “like” powdery mildew because it shows similar symptoms

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David Doll5 CommentsMarch 6, 2019Diseases, Horticulture

Timing Fungicide Sprays: Thoughts for a Wet Spring

Improper timing of fungicides wastes money and leads to crop loss from disease. Over the years, I have seen several disease epidemics that were due to the improper timing of a fungicide spray. These were observed in both wet and dry years, indicating the difficulty and general misunderstanding of disease and spray application timing. Proper timing of fungicide applications is difficult. Operational constraints in applying fungicides leads to mis-timed (too early, too late) or poor applications (every other row, applying too fast). This is often a function of equipment availability, whether by grower/operation or custom applied spray. Add to this aspect the various layers of fungicide availability and delivery timing, the changing pathogens and disease conditions, as well as the general misconceptions of various diseases, it is very easy for problems to occur. In order to control diseases, as advocated in earlier postings, it is best to design a fungicide plan prior to the start of the season. This provides the opportunity to review reference materials and determine which fungicides are best for differing stages of the crop. This plan also creates the opportunity to provide options for differing modes of actions at each timing to help with pricing, and reduces the burden of having to put the plan together when the season has started (and there are several other demands). Personally, I like to design the plan for a wet year and remove fungicide timings if dry conditions occur. An example of a plan with different modes of actions can be found here. Diseases don’t just occur. They require a susceptible host, the presence of a pathogen and suitable environmental conditions. For most almond foliar or bloom diseases, the pathogen is throughout the environment and most of our varieties are susceptible to one disease or another. The largest variable

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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 Doll3 CommentsJanuary 1, 2015Diseases

Bacterial Spot of Almond in California: Update on the Disease and Management

written by Dr. Jim Adaskaveg (UC Riverside), Brent Holtz (UCCE San Joaquin), Roger Duncan (UCCE Stanislaus), and David Doll (UCCE Merced).   In the spring of 2013, we reported a high incidence of bacterial spot in some Sacramento and northern San Joaquin Valley almond orchards, especially on the ‘Fritz’ variety.  It was also found on ‘Nonpareil’, ‘Butte’, ‘Carmel’, ‘Monterey,’ and ‘Price’ but at much lower levels.  The disease has not been found in orchards in the southern San Joaquin valley. Bacterial spot is caused by Xanthomonas arboricola pv. pruni and has also been referred to as bacteriosis, bacterial leaf spot, or bacterial shot hole. Bacterial spot occurs on leaves, twigs, and fruit of almost all Prunus spp.  The pathogen commonly causes bacterial spot of peach in the eastern United States and is one of the major foliar diseases in high rainfall years. On almonds, it is a significant problem in Australia because of mid-season rain events.  In 2014, we verified the presence of the disease at previous and additional locations in California, although at levels much lower than in 2013.

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Roger Duncan7 CommentsJanuary 21, 2014Diseases

Bacterial Spot Management

Almond growers and pest control advisors who attended our July bacterial spot field day in Manteca saw how devastating this new disease can be.  A map passed around at that field day showed two hot spots for the disease in our area.  The most severely affected area was between Highway 120 and the Stanislaus River in the Manteca/Ripon/Escalon area.  The second area was south of Turlock in the Delhi / Ballico area. 

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