David Doll0 commentsFebruary 15, 2011Diseases

Some more bloom time thoughts…

Yesterday, I had a nice chat with Dr. Jim Adaskaveg, UC Specialist in Plant Pathology. As many of you may know, Dr. Adaskaveg conducts many of our foliar and bloom disease trials. Here were some additional comments to be added about bloom spray timing and last week’s post. Dr. Adaskaveg highlighted that all parts of the flower are susceptible, but for the most part the flower petal is the most susceptible and is the primary point of flower infection. Many of the fungicides used have what Dr. Adaskaveg termed “Reach Back Potential.” This basically means that a fungicide application controls the growth of infections that may have occurred BEFORE the fungicide application. In these cases, the fungicide does not serve as a curative, but rather as a fungal-static agent, or, in other words,  it slows the growth of the fungus but does not kill it. This provides more time for fertilization and petal abscission to occur, thus reducing brown rot incidence. He also pointed out that Brown Rot is most active in temperatures above 57 degrees F. It is important to note that infection can still occur below 57F, but the rate of growth is reduced. He suggested that growers with brown rot tolerant varieties (i.e. Nonpareil) and no history of brown rot may be able to get by with a minimal spray program. In some cases he observed 50% Nonpareil orchards in which the grower did not spray the Nonpareil; fungicides were applied only to the pollinators. This practice was not recommended for Butte plantings. Butte is very susceptible to brown rot. In regards to the upcoming weather and the beginning of bloom, he suggested holding the first spray until after the rains, trying to hit the 30% bloom mark on Nonpareil.This should provide coverage for the emerged Sonora blossoms. He felt comfortable with

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David Doll2 CommentsJanuary 27, 2011Horticulture, Nutrient

Bloom Spray Additives: Do they work?

Bloom is approaching. Several questions about whether or not bloom spray additives increase flower pollination and set have been asked. I will try and answer them the best I can using information from previous trials across the state. Much of this information is gleaned from Roger Duncan’s presentation delivered at the 2010 Stanislaus Almond Day. Should I include foliar nutrients in the bloom spray?Several trials from four different advisors from areas across the state (Duncan – Stanislaus, Holtz-Madera, and Edstrom – Colusa, and Viveros – Kern) have indicated that nutrients and other additives included with bloom sprays do not increase yield of almonds in properly maintained orchards. In most trials, yields of the untreated control were higher than the foliar nutrient applied treatment. These were multiple replicated trials held over several years. Materials used can be seen by viewing the presentation linked below. This trial data can be seen in Roger Duncan’s 2010 NSJV Almond Day presentation (click link). What about Pristine® Fungicide?Pristine® fungicides is a boscalid/strobilurin mixture that has been used successfully for several foliar fungi that commonly affect almond flowers and leaves (i.e. Brown Rot, Rust, Scab, etc.). There is evidence that suggests that Pristine® causes a yield bump when applied during the bloom or post bloom period. Research by Jim Adascaveg (UC Riverside) and Roger Duncan (UCCE Stanislaus) tested this hypothesis and have not found a significant increase in yield from a bloom or post bloom Pristine® application. It is important to state that in Duncan’s trials (Stanislaus Co.), the yields were higher in treatments containing Pristine®, although not statistically significant. Duncan found this same insignificant yield bump when applying Gem®, another strobilurin, in the post-petal fall period. Conversations with a local consultant indicated mixed success of the Pristine® yield bump across his multi-year trial. Although he

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David Doll9 CommentsFebruary 23, 2010Diseases

Almond Anthracnose – An ugly spring disease

Anthracnose (Colletotrichum gloeosporioides) is a damaging fungal disease that attacks the blossoms, leaves, fruit, and limbs of an almond tree. Infected leaves tend to develop water-soaked lesions that eventually fade in color (Figure 1). Defoliation can occur, but leaves often remain attached to the branches. Infected nuts often have a crater-like lesion in which the affected area turns a reddish orange(Figure 2). Often, the fruit may gum profusely as the fungus is able to penetrate into the kernel, killing the embryo. Affected nuts often remained attached to the spur(Figure 3). Shoots and spurs that bear infected nuts often become infected and die(Figure 4). Lack of culturing the fungus from these branches suggests that the wood does not die by direct fungal colonization, but by a produced toxin. Thus, this disease affects the current year’s crop as well as affecting the future crop by damaging and weakening the affected scaffolds.Figure 1: Almond leaves infected by Anthracnose. Figure 2: Anthracnose infection of an almond. Note the profuse gumming coming from the kernal. Anthracnose is most severe in wet, warm springs (> 60F). Orchards that have a history of anthracnose should be treated during bloom (pink tip forward) to help protect blossoms. Repeated fungicide applications may be necessary through the spring as trees should be protected before rain events. Fungicides provide protection for up to 7-10 days, and rain events occurring beyond this “control window” may require another spray. All varieties are susceptible to Anthracnose, but they vary in their degree of susceptibility. Butte, Thompson, Merced, Price, Peerless, Winters, Monterey and Fritz are the most susceptible varieties. Harvey, Carmel, Ne Plus Ultra, Padre and Mission are moderately susceptible, with Nonpareil being the least susceptible. Figure 3: Kernals killed by anthracnose often remain on the tree as dried, shriveled mummies. Figure 4: Anthracnose infection

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David Doll2 CommentsFebruary 23, 2010Diseases

UPDATE: DMI Fungicides and Botrytis Control

Last week, I suggested the use of DMIs (Quash, Indar, Inspire, Rally, etc.) for brown rot control spray program. A fellow reader shared some experiences with me regarding the use of DMI fungicides during the late bloom period. Although DMIs are good for brown rot, anthracnose, and have some activity against scab, shothole and rust, they do not provide control for the fungus Botrytis, which causes jacket rot and green fruit rot (Photo above). Botrytis is found everywhere and grows rapidly in cool, moist weather. It typically infects young almond jacket and fruit, causing infection and nut abortion. It is greyish in appearance, and affects varieties that cluster – Avalon, for example. It is not found frequently, but when found, is typically in orchards that have only used DMI fungicides. Therefore, if your last fungicide application is a DMI, I would advise to include a broad spectrum as a tank mix (chlorothalonil, Captan, Maneb, Rovral) to help reduce the incidence of Botrytis infection. Any other thoughts on this?

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David Doll1 CommentFebruary 15, 2010Diseases

Brown Rot: A disease problem during bloom

Almond orchards are treated at least once during bloom for fungal disease brown rot. Rightfully so, as the brown rot fungi (Monilinia laxa) can kill the flower, fruiting spurs, and shoots. Flowers are susceptible from pink bud to petal fall, and are most susceptible when flowers are fully open. The fungus is able to infect all parts of the flower: anthers, pistils, petals, and stigmas (Figure 1). Upon killing the flower, it can move into and kill woodier tissues of the tree. Once in the woodier tissue, it forms a canker (Figure 2). This canker can enlarge to kill the branch and also serves as the survival structure for the fungus. These cankers are the reason why it takes many years to “clean up” an orchard after a severe brown rot infection. Brown rot can also infect the jacket of the almond and kill the young fruit as well. This is called jacket rot. Figure 1: Blossom blight of almond caused by the brown rot fungus Monilinia laxa.All varieties are susceptible to brown rot, but they vary in their degree of susceptibility. Butte is the most susceptible variety followed by Carmel. Ne Plus Ultra and Mission are moderately susceptible, while Nonpareil and Peerless are the least susceptible to brown rot. Brown Rot Blossom blight is usually controlled with a pink bud and full bloom treatment. Many of Brent Holtz’s (UCCE San Joaquin) trials suggest that the full bloom treatment may be the most important. A third petal fall spray may be necessary in years favorable to disease (rain). If bloom is strung out and the weather is wet and rainy, no more than ten days should elapse between treatments. A few growers have told me that they do not spray for brown rot. This may be okay if good conditions

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Brent Holtz0 commentsFebruary 2, 2010Diseases

Bloom sprays: What and when to use to provide effective disease control.

Written by Brent Holtz, UCCE San Joaquin Almond trees are susceptible to bloom and foliar diseases when it rains at bloom, and the decision of when to spray and what fungicides to use can be quite difficult. In the San Joaquin Valley we are usually in a low precipitation region and we cannot predict when and how much it is going to rain. We often receive rain during bloom which can result in favorable conditions for several plant pathogenic fungi to cause spring time diseases of almonds. The main diseases in almonds are Brown Rot Blossom Blight, Green Fruit Rot or Jacket Rot, and Shothole. Other less familiar diseases include Scab, Rust, Leaf Blight and Anthracnose. The fungi that cause these diseases are usually always present in almond orchards, sometimes in higher or lower amounts depending on the previous year’s disease levels and current environmental conditions. Fungicide Control ProgramsGenerally, a good disease control program is based upon a wise choice of fungicides and good timing and coverage. Growers should assess the diseases present in their orchards and select materials carefully. Not all fungicides are equally effective on all diseases (fig. 1). It is a good idea to use more than one kind of fungicide for a broader spectrum of activity. This will be especially important with using Strobilurin fungicides (Abound, Cabrio, Flint, Sovran, and Pristine). Pristine is a Strobilurin fungicide that is combined with Carboxyanilide to slow resistance development. Resistance to these fungicides can develop over time and repeated use, thus try to rotate the fungicides you use. Two successive applications of the same mode of action should be avoided. Information on effective fungicide rotations can be found in figure 2. A suggested bloom spray strategy:Usually two sprays are made for brown rot control. The first is usually done at

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