David Doll0 commentsApril 17, 2017Diseases

Alternaria leaf spot of almond

The late rains we are receiving will increase the risk of Alternaria. This pathogen (Alternaria alternata) requires warm temperatures and leaf wetness to infect almond trees. A few weeks after infection, small circular lesions form, eventually increasing to the diameter of 1/2-3/4.” Occasionally, there is a yellow halo. Older lesions often develop a black ring of spores. Typically, the leaves are infected in mid- to -late April or May, with the symptoms occurring several weeks later. The disease develops rapidly in the summer, especially when there are heavy dews. The varieties ‘Carmel,’ ‘Sonora,’ ‘Monterey,’ ‘Winters,’ and ‘Butte’ are more susceptible than other varieties. This problem tends to be more frequent and severe in the south San Joaquin Valley and the western side of the Sacramento valley. In wet years, severe problems occur throughout California. Alternaria can be managed by utilizing cultural practices and fungicide sprays. Orchards with high humidity, heavy dew, and stagnate air often have severe problems. Selected pruning of the canopy can help increase ventilation. Improving water infiltration can reduce orchard humidity. When designing an orchard, rows should be oriented in parallel to prevailing winds to assist with ventilation. Other practices that assist in reducing leaf wetness and canopy humidity should be considered. Fungicides should be considered if the orchard or area has a history of the disease. Orchards should be scouted for signs of the disease in April through June. If Alternaria is found, treatments should begin – usually about mid-April. In orchards with a history of the disease, treat in mid- to late April and 2 to 3 weeks later. FRAC groups 3, 7, 11, and 19 used alone or in combination are effective in preventing disease. If making multiple sprays, fungicides should be rotated to prevent the formation of resistance. More information on fungicide selection can be found here.

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David Doll7 CommentsMarch 17, 2017Diseases

Bacterial Canker and Blast

Over the past few weeks, there have been a high frequency of problems reported with bacterial canker and blast. Bacterial blast results in blighted blossoms and causes crop loss. Interestingly, when there is a high frequency of blast, the very similar disease of bacterial canker appears a few weeks later in young trees(we are starting to get reports of canker now). Both of these problems are complicated. They involve the bacterium Pseudomonas syringae, plant stress which is often mediated by nematodes, and the weather. P. syringae is an interesting bacteria. It lives naturally on plant surfaces as an epiphyte – meaning that it generally does not cause problems. During wet winters which create a favorable environment, bacterial populations increase and spread through the tree and orchard. At some point the population becomes large enough that it begins to invade plant tissues – starting with buds (bud drop), then flowers (blast), and finally bud scars and other openings which leads to bacterial canker. Tree health has a lot to do with the susceptibility to P. syringae infection. Generally, if the tree is healthy, infections rarely occur. Weak, young trees- usually three years or less- are susceptible to bacterial canker which can cause the loss of tree scaffolds or death. Mature orchards usually don’t exhibit bacterial canker symptoms, but rather have blast and bud drop problems. Orchards with severe problems are typically planted in sandy soils, which often tend to be acidic, hold less water and nutrients as well as being more conducive to plant parasitic nematodes. All of these factors, if managed improperly, can increase tree stress, increasing susceptibility. Some micronutrient deficiencies, notably iron, have been found to increase susceptibility, while balanced, proper major nutrient fertilization has been shown to reduce occurrence.  Severe water stress can also increase occurrence, and is thought to be due

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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 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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Emily Symmes2 CommentsJanuary 24, 2017Diseases, General, Insects

Protecting Honey Bees During Bloom

Written by Emily J. Symmes, UCCE Sacramento Valley IPM Advisor With almond bloom on the horizon, it is time to revisit best management practices for protecting pollinators (e.g. honey bees) during this critical time. Remember that communication is key during the bloom period. All parties should be kept informed so that beekeepers are aware of impending applications and applicators are aware of the requirements related to notification, materials, timing, location, and method of application. This includes growers, beekeepers, land owners-lessees, PCAs/CCAs, pesticide applicators, and county Agricultural Commissioners. General guidelines: Employ sound IPM practices: Apply pesticides only when absolutely necessary based on monitoring and treatment thresholds. Know all of the available materials and application timings. For insect pests, there are effective alternative timings for insecticide applications aside from the bloom period. If the weather remains dry and clear throughout bloom, there should be minimal need to apply bloom fungicides. One solid application just ahead of full bloom should be adequate for good disease control under these conditions. Earlier spray timings (e.g. pink bud) if wanted, may be applied every-other-row. Be aware of the impacts of any treatments on pollinators and other non-target organisms. Always provide adequate clean water for bees: Cover or remove water sources prior to any application. Keep water clean and fresh ensuring bees spend more time pollinating the crop than searching for water. Bees can forage up to 5 miles away seeking food and water if not available in the orchard, increasing their risk of contact with harmful pesticides. Do not spray hives directly with any pesticide. Ensure the spray-rig driver turns off nozzles when near hives. Do not spray flying bees with any applications. Aside from toxicity concerns, bees will not be able to fly because of the weight of spray droplets on their wings. Even water

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David Doll0 commentsSeptember 14, 2016Diseases

Defoliating for Rust Management…Good Idea?

Written by David Doll (UCCE Merced County) and Brent Holtz (UCCE San Joaquin County) The foliar disease rust caused by the fungus Tranzschelia discolor has been a major problem this year. This disease is characterized by rusty-brown- or black-colored spores that form on the lower side and angular chlorotic (yellow) lesions on the upper side of the leaf. Rust can spread easily from orchard to orchard with wind, and minimal periods of leaf wetness are required for the pathogen to infect. This past year, long periods of conducive conditions, which include warmer temperatures, late spring rains, and increased canopy humidity were experienced, making rust management a challenge. Rust is easily controlled by properly timed fungicides. Several modes of action provide protection. Those with the highest activity are FRAC Groups 3, 11, and 19 or mixtures of these groups. Also several broad-spectrum fungicides such as micronized sulfur (M2, microthiol) and chlorothalonil (M5, Bravo) have very good efficacy with short- and long-residual activity, respectively. Since rust can infect from spring to summer, sprays need to be timed accordingly. Spring sprays (2-5 weeks after petal fall) based on monitoring for rust symptoms is often used to initiate rust control practices at the beginning of a potential epidemic. One fungicide application, however, may not provide effective control if favorable conditions persist and later sprays may be needed. Typically, spring-time disease management programs for scab and Alternaria leaf spot will also provide management for rust. High populations of rust can prematurely defoliate trees. As the fungus spreads, it ruptures leaf tissues, reducing the photosynthetic potential of the leaf, and eventually causes leaves to fall. If too many leaves fall from the tree, the tree will re-leaf, reducing the cropping potential for next year. Although this re-leafing is concerning, it is better for the tree to re-leaf

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David Doll5 CommentsAugust 29, 2016Diseases, General

Considerations for Replanting Almond Orchards

It is the time of the year when many operations begin the process of replanting almond orchards. Orchard removal and eventual replacement is one of the more critical times of farm operations. The decision to remove a block varies by farmer. Some remove blocks based on a cycle of redevelopment, meaning that blocks are removed on a schedule based on age to assist with cash-flow. Some are removed due to expensive or inadequate resources (e.g. water). Many are removed when production drops below a certain profitability level. Removing a block on profitability can be tricky. Blocks tend to alternate bear. An off year may trigger removal, but it could be coming into an on year. Prices also fluctuate. Therefore, this may not be the best way to decide on removing a block. Another consideration should be determining the the stand of trees remaining in the orchard and the rate of tree loss over the past few years. Commonly, in old orchards, trees are lost to heart rot decay fungi and corresponding wind throw. These losses tend to increase as the orchard ages. If this rate is increasing and the orchard stand is below 75%, removal and replanting should be considered. This is a conservative estimate, and should be evaluated with production records and tree stand for your own operations (This estimate is based on an 80% canopy coverage at maturity with minimal tree losses). Once the decision to remove is made, the work begins. Consider harvesting the later varieties earlier to allow more time in the process.  Nematode sampling should occur prior to removal to determine which species are present and assist in rootstock selection. This can be done one to two years prior to removal. Line up the resources for orchard removal, which can be done by tub grinders, whole orchard incorporation, or removal

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David Doll2 CommentsMay 14, 2016Diseases

Verticillium Wilt of Almond (and Pistachio)

The high heats of late spring/early summer can bring upon the onset of wilts. Verticillium wilt, a common occurring wilt, is caused by the fungus Verticillium dahliae Klebs. V. dahliae is widespread in soils throughout the county, with susceptible hosts in a large number of perennial and annual crops. Within perennial crops, almond and pistachio are susceptible hosts. Leaves turn light tan and die, and often remain on the tree. In some cases, particularly in pistachio, symptoms develop slowly over several years causing a thinning of the leaves and a corresponding loss in yield as the fungus progresses up the branch. Internally, the xylem wood turns dark, and a cross section will show a ring of discolored tissue. This darkened tissue will extend down the affected scaffold to the point of origin within the root system. Several scaffolds of the tree may be involved if the pathogen infected a large portion of roots. The fungus survives in the soil within survival structures known as microsclerotia. It enters the trees through the roots, infecting the xylem tissues of the plant. Upon infection, the fungus produces a dark pigmented substance that clogs the xylem tissues, preventing the upward flow of water to the scaffold branches. When the affected branches or leaves demand more water than it can receive due to the blockage, it collapses. Cool springs and wet soils favor disease development. The fungus is eliminated from the above-ground portions of the trees during the hot weather. The fungus may survive within the root and reinvade the upper part of the tree, but it is thought that repeated occurrences of wilt are caused by new infections each year. Within almond, young trees within their 2nd and 3rd leaf are the most susceptible to tree loss. All almond rootstocks and varieties are susceptible,

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David Doll6 CommentsMarch 14, 2016Diseases, Horticulture

Yellow Trees and Saturated Soils

Annually, several calls regarding poor tree growth and “pale trees” are received. This is often due to saturated soils. Too wet of soils reduces the movement of oxygen into the soil, killing fine feeder roots. This impacts the ability for the tree to uptake water and nutrients, leading to micro-nutrient deficiencies, impacting nut set and tree growth. Later-season effects are also observed and include a limited rootzone, leading to severe water stress during hull-split and harvest. The problem is often compounded by farm practices. Too early of fertigations before the tree begins to “suck” water from the soil can lead to an increase in saturated conditions. Spring rains, cool temperatures, and heavy soils compound the problem. Once the symptoms appear, the reaction is to fertigate or chemigate in attempts to manage the symptoms of stunted growth and yellow leaves. Symptoms continue to worsen. Recovery is not always possible. If conditions are prolonged, the symptoms will worsen. Trees may eventually die or shed leaves and crop. In some cases, the roots and crown may become infested with Phytophthora. In many cases, Phytophthora is serving as a secondary problem, infecting only after the tree has been weakened by the saturated soils. The problem can be alleviated by warmer temperatures which increase the transpiration rate of the tree or reduced irrigation until the tree recovers. Recovery is dependent on severity, and may take several months. Optimally, it is best to do what is possible to prevent the symptoms from occurring. Prior to the first irrigation, moisture levels in the soil should be dropping. This can be determined with the use of a shovel or auger, pressure chamber, or soil moisture sensors. If using the pressure chamber, irrigation should be considered if trees are 1-2 bars more negative than baseline. More on using the pressure bomb to

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