David Doll0 commentsApril 6, 2015General

Mid-Spring Considerations/Update

The 2015 almond season is in full swing. Many orchards have went through their drop, fertilizer applications and irrigation have began, and pest management concerns are beginning to form. Below are some thoughts and considerations from recent field visits. 1. Crop development is ahead of schedule – by as much as a month. Kernel fill is beginning in many ‘Nonpareil’ orchards, meaning that ‘Butte’/’Padre’ orchards won’t be far behind. This timing is important as about 80% of the season’s nitrogen budget should be applied prior to kernel fill – which may occur as early as early May! Secondly, it indicates that at this point – “What you see is what you’ll maximally get” in regards to kernel size, and farming practices – more particularly irrigation practices – can only reduce crop size. 2. Peach Twig Borer’s (PTB) “May Spray” timing looks to be an April timing. In the Merced area, our traps picked up a biofix around March 15th, which means we will be approaching 300 DD in about 7-10 days. Keep in mind that the spring spray timing for PTB is 300-400 degree days after the biofix. It may also be possible for the May Spray to have some effect on NOW.  Frank Zalom (UC Davis Entomologist) has found through research trials that timing the spray to 100 DD post NOW biofix (egg traps) and around 400 DD post PTB biofix can provide good control of NOW and PTB at harvest. 3. Rain is predicted for Tuesday (the 7th). Hopefully some rain will fall in the valley to help with the multitude of water issues. This rain may also bring some potential for fungal disease – especially rust and scab. Consider an application if there has been a history of disease. This application can be made 1-2 days after the rain event and

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David Doll2 CommentsJanuary 15, 2013Diseases

Chlorothalonil and Oil: Dormant Application Q&A

I have been receiving quite a few questions about the application of chlorothalonil and oil. This dormant spray has been shown to be highly effective in reducing in season scab, as well as delaying the sporulation of the pathogen, making in-season fungicide sprays more effective. Q. The work by Dr. Adaskaveg shows 6 pts, the product is only registered for four (winter, 2013)…is the 4pt rate effective?

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David Doll2 CommentsMarch 16, 2012Diseases

Scab Spray Timing and Other Spring Disease Questions

Wet weather has found its way into the valley, with rain events predicted off-and-on for the next week to 10 days. I have had a few questions regarding fungicide applications. Chlorothalonil (i.e. Bravo) isn’t registered for jacket rot of almond? Should I tank mix in another fungicide to provide protection? Figure 1: Overwintering scab lesions on the green wood of almonds. That is correct – Almond jacket rot is not on the label for chlorothalonil. Therefore, if a recommendation is written for jacket rot, another labeled fungicide must be used. FYI – chlorothalonil is labeled for jacket rot of apricot, which is caused by the same pathogens (Botrytis cinerea, Sclerotinia sclerotiorum, Monilinia laxa,Monilinia fructicola). What is the best time to apply a fungicide for Scab? Scab (Cladosporium carphophilum) overwinters on twigs of almonds (Figure 1) and will re-infect new leaves shortly after leaf out. Control of this diseases has been documented with dormant applications, petal fall applications, and applications made 2-5 weeks after petal fall. Earlier post-petal fall applications (~2 weeks) provides more effective control than later applications. Figure 2: Scab lesions sporulating on an almond branch. Note the darkened circles within the lesion. Fungicides should be applied for protection when this is observed to prevent scab infection. Photo courtesy of the Almond Board of California. The timing of the fungicide application should be made when the overwintering scab lesions begins to sporulate (release spores into the orchard).  When sporulating, the lesions, which are found on the green twigs of the tree, will develop a dark ring (Figure 2). Providing protection of the leaves with fungicides at this point will help reduce/prevent scab infection of the almond trees. Is there any way of determining if we are going to have another bad year of rust or scab? Predicting disease epidemics is challenging. Basic epidemiology indicates

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David Doll0 commentsFebruary 2, 2012Diseases

Chlorothalonil and Oil for Scab Control — To Late? Yes.

Figure 1: The effect of dormant treatments on the incidence of almond scab sporulation. Observations were made on May 3rd, 2011. Different letters indicate significant treatment differences at p<0.05. There has been quite a bit of talk about the use of Chlorothalonil and oil applied during dormant for Scab control. Although this treatment has shown to reduce overwintering scab populations and delay scab lesion sporulation (Figure 1), caution needs to be taken when considering application. This product needs to be applied when the tree is completely dormant. Once the tree starts to push and the buds begin to swell/green tissue appears at the tip (Figure 2), avoid using this spray treatment. Chlorothalonil mixed with oil applied to green tissue will kill the green tissue, explaining why this product is labeled for dormant use no later than December. Figure 2: Delayed dormant stage of an almond bud. Note the bud swell and exposed green tissues. If a dormant scab treatment is to be applied at this time (delayed dormant/bud swell), consider making an application of copper and oil. This treatment has also been shown to be quite effective (Figure 1), especially when used in combination with in-season scab sprays timed 2-5 weeks post petal fall.

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David Doll0 commentsAugust 12, 2011Diseases

Summer Foliar Disease Epidemics – Scab

Scab lesions found on almond twigs. I have scab all over my orchard. What can I do? Short answer – nothing. It is too late to expect control of the disease. Once the fungus infects the leaf and produces visible symptoms, that is a clear indication that the fungus has colonized the inside of the leaf. No fungicide completely penetrates the leaf surface, which makes it impossible to cure an infected leaf. Furthermore, spraying a fungicide upon seeing a disease epidemic will end up doing more harm than good. Since the fungus has completed it’s life cycle several times (Scab is a polycyclic disease), the population within the orchard is so high that making an application can lead to the selection of a fungicide resistant strain of scab. Scab lesions found on the underside of almond leaves. If every tree has scab, what can I expect? Defoliation. As the fungus colonizes the leaf, it begins producing spores which are the reproductive structures of the fungus. These spores are produced and move from an infected leaf to a healthy leaf. Upon complete colonization, the tree detects that the leaf is infected, forms an abscission layer which causes the leaf to fall from the tree. If enough leaves are infected on the tree, total defoliation can occur – and in most cases, is expected. Symptoms of scab observed on the top-side of almond leaves. What should I do? Since scab overwinters on the infected twigs in the form of lesions/fruiting bodies, population reduction is based upon controlling the disease present within the field, and coverage of susceptible tissues in the spring. Dormant applications of of copper and oil or chlorothalonil and oil have been shown to reduce summer populations of scab, and are recommended in orchards that have experienced leaf loss the previous summer/fall. Prophylactic sprays

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David Doll0 commentsApril 6, 2011Diseases

Late Scab Timings for Almonds

Early season Scab lesions on almond. We are approaching the end of the effective almond scab control spray timings. Scab has become more common in area orchards due to the increased planting density and occurrence of wet springs. Causing defoliation in late summer, this disease can weaken the tree, reducing crop for the coming years. A heavily infected orchard will have persistent scab issues for several years after the disease flare up. Fritz and Carmel are more susceptible to this disease than Nonpareil and other varieties This spray period starts at about 2 weeks after petal fall and continues to about 5 weeks after petal fall. Years of research by Dr. Jim Adaskaveg and Dr. Brent Holtz have demonstrated that spraying during this period provides the greatest control. The use of strobilurins (FRAC 11 – Gem, Abound, Pristine) provides the greatest control of this disease, followed by the DMIs (FRAC 3 – Quash, Inspire, Inspire Super, Bumper, Tilt), Topsin-M (FRAC 1), and broad spectrums (Captan, Maneb, Ziram, etc). Overwintering scab twig lesions. It is speculated that strobilurin resistant populations of scab are becoming more common. Applying back-to-back applications of strobilurins will hasten the development of resistance. If you sprayed a strobilurin earlier this bloom season you must consider another mode of action for scab control. Earlier entries emphasized the importance of saving this mode of action for summer diseases.  Sprays must be made within the 2 – 5 week petal fall period to provide maximum control. Later sprays will not be as effective. Waiting till the disease is visible before you start to spray is not advise as the population at that point is too high to control. In many cases, spraying at this point will only waste money AND increase the risk of fungicide resistance.  Orchards with severe outbreaks should consider a dormant application of copper/oil to

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