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 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 Doll2 CommentsFebruary 7, 2018Diseases, Irrigation

2018 Almond Bloom Considerations

2018 almond bloom is around the corner. This year will probably be one of the earliest almond blooms we have had in Merced County. This accelerated bloom is due to the warmer, sunny weather experienced through January. Depending on conditions following flowering, hull-split and harvest should also be earlier. Weather for the coming bloom period looks to be favorable for the San Joaquin Valley. Warm conditions (temperatures in the 70’s) and no rain in the forecast provides the conditions that are conducive for rapid flower development. Thankfully, these conditions will not favor disease. Early bloom sprays may not be needed for many tolerant varieties (e.g. Nonpareil), unless heavy dew and susceptible varieties (i.e. Butte) are present. Regardless of weather, a fungicide spray made at full bloom/petal fall should be considered. This fungicide should provide protection for brown rot, shot-hole and jacket rot. Of these three, jacket rot is one of the harder fungi to control with the modern fungicide chemistries as the strobilurins (FRAC 11) and DMIs (FRAC 3) are not effective. This spray timing will provide protection for any rain events that would occur within two weeks of application. Successive in-season sprays may be needed if the weather turns wet. Further information reagrding fungicide timing and efficacy can be found here: http://ipm.ucanr.edu/PDF/PMG/fungicideefficacytiming.pdf . Fungicide applications should be made at a time of day to reduce bee exposure. Applications later in the day will reduce exposure as bee foraging is decreased in the afternoon. If applying at night, allow enough time for the fungicide dry before bee foraging begins the next day. Also, avoid any addition of surfactants with the fungicide unless directed by the fungicide label. Many more management practices for bees can be found at The Almond Board of California’s website: http://www.almonds.com/pollination . The first irrigation will be tricky

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David Doll2 CommentsFebruary 9, 2017Diseases

Almond Bloom 2017

Almond bloom is approaching fast. Based on local conditions and projected warm weather next week, bloom will probably be within 7-10 days. Conditions this year are wetter than they have been in the past which will be conducive to many almond diseases, including brown rot, shot-hole, anthracnose, and jacket rot. Furthermore, orchard access may be limited, reducing the ability to apply fungicides by ground rigs reducing coverage. Below are a few points to consider as we begin the 2017 season. Be prepared for several fungicide sprays. If wet conditions persist, a more conventional bloom spray program should be considered with an application around pink bud to 20% bloom,  an application at 80% bloom, and a petal fall spray. These regular sprays ensure coverage of the expanding floral tissues. Sprays should be made every 10 to 14 days in consistent rain, and every seven to ten days if  heavy rains are experienced.   Fungicide rotation is critical. With multiple fungicide applications, each successive spray should be a different fungicide mode of action. This is represented by the FRAC number. If using multi-mode of action fungicides, the fungicide used in the follow up spray needs to be different than both modes of actions utilized in the previous spray. Please review the modes of action for the various diseases and timings by using the Fungicide Efficacy tables outlined here. Almond relevant information is on page 31. Often wet winters are followed by wet springs. With the potential need of fungicides through the spring, it may be useful to mix in a broad spectrum fungicide at petal fall. This would provide the ability to apply the same mode of action twice in the same season. A spray program with this type of rotation could look like this: Pink bud: FRAC 9; Full Bloom: FRAC 3/11; Petal Fall:

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David Doll8 CommentsFebruary 15, 2016Horticulture

2016 Almond Bloom Considerations

Adequate chill and recent warm temperatures have accelerated almond bloom. Timing is close to “normal” in southern and southwestern areas of the State, but are 1-3 weeks ahead further north. Below are some thoughts to keep in mind with the anticipation of rain this week. Authors note (2-16-2015): There has been some concern about the wording around the time of nutrient/boron sprays and bloom. Research has shown that boron applied postharvest to 10% bloom can increase yield, while applied later than 10% bloom will not have an impact. Nutrient sprays-with the exception of boron as described in the previous sentence- have not been found by researchers to increase yield when applied at bloom. Sorry for the confusion. Fungicides are usually effective for about 14 days after an application. This period of protection is decreased with rain events. Furthermore, as surface areas expands – whether it is the flowers or leaves – newly exposed tissues are unprotected from infection. This means that spraying too early may not provide the wanted protection. If planning to make a fungicide application, apply the material as close to the rain event as possible. Remember that it needs between 30-60 minutes to dry. Depending on the pre- and post-rain conditions, and the periods of leaf wetness, a fungicide spray may not be needed. Keep in mind that fungal diseases require several hour periods of leaf wetness – which comes from fog, dew, and rain. Be cautious with adding additional surfactants. Most fungicides have surfactants mixed with the active ingredient. Adding additional surfactants may impact the efficacy of the fungicide, damage the flower’s tender tissues, or impact bees. The label should indicate if a surfactant is needed. Avoid tank mixing in boric acid with sprays made during bloom when bees are active(1). Researchers at the University of California as well as around

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David Doll1 CommentJanuary 18, 2016Insects

Bloom Bt for Peach Twig Borer Control

Written by John Edstrom, UCCE Farm Advisor Colusa County, Emeritus Hopefully, the central valley will finally receive drought relief from recent El Niño driven storms. The resulting wet soil conditions, however, can prevent orchard access for many orchard operations including dormant sprays. Without dormant insecticide sprays, peach twig borer (PTB) populations can increase dramatically and threaten next years crop. Worm reject levels were troublesome and costly to many almond growers this past season and point to the need to control PTB. Besides kernel damage, twig borer feeding also kills young buds and shoot tips after bloom and deforms young tree scaffold limb development . Fortunately, growers have a very safe alternative to dormant sprays using Bacillus thuringiensis (or Bt) to control PTB during the bloom season without harmful side effects to applicators or the environment. Other insecticidal materials claim to be safe to bees but may negatively impact bee colony health. Bt has no adverse affects to any stage of honeybees or the health of the hive.  Bt is a natural bacterial based insecticide that is toxic only when ingested by lepidopteran larval stage pests and is completely safe to beneficial predators and parasitoids. Bt is exempt from pesticide use regulations and so is particularly useful near urban or environmentally sensitive areas. The bloom Bt control strategy has proven effective since its was developed in the 1990s during a time when regulations were restricting the use of the highly toxic organophosphate spray materials. Bt is a perfect fit for almond IPM programs. Its only down side is that multiple applications are needed for complete control. Fortunately, Bt products are inexpensive and can be tank mixed with fungicides applied for blossom and leaf diseases around bloom, so the total costs are comparable or less than standard insecticides. Generally, two sprays are

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David Doll4 CommentsFebruary 7, 2015Diseases

Almond Bloom 2015

Bloom is around the corner. After receiving adequate chill units through December (almonds need ~400-500), almonds switch from ‘chill accumulation’ mode to ‘heat accumulation mode.’ Although less is known about this stage for many crops, it is known that a certain amount of heat is needed in order for bloom to begin. This heat requirement keeps the plant from blooming too early, reducing the risk for the impacts of frost events. The warmer weather over the past few weeks, however, has provided conditions that have met the heat requirement for most areas of CA. This suggests that if the weather stays warm through the next week, bloom will begin for more areas within California. Below are some considerations to have in mind for bloom: Fungicide sprays. Due to the sensitivity of almond flowers to disease and conditions during bloom that are conducive for disease, most people will spray a fungicide during this period. In wet conditions, multiple sprays may be needed, while in dry years a single or no spray may suffice. Conditions that favor disease formation include wet weather, warmer temperatures for Brown Rot, Anthracnose, Bacterial Spot, and Shot-hole, cool weather for Botrytis, and heavy dew. Fungicide selection should provide coverage for the diseases of concern (Please see this link and scroll to ‘Almonds’). Bloom sprays should be applied before rain events to provide protection for flowers, flower parts, and emerging leaf tissue. Coverage from a fungicide spray will last around two weeks, unless significant rainfall occurs.  If applying prior to a rain event, applications will need a few hours to dry to prevent “run-off.” In rainy weather, follow-up sprays will be needed every 7-10 days. Some varieties – such as ‘Butte’ and ‘Carmel’- are more susceptible to disease and may require a spray even in dry weather, while others – such as

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