David Doll0 commentsFebruary 27, 2013Diseases

No Rain at Bloom – Some Q&A

Looking at the 12 day forecast, it looks like it is going to be a dry couple of weeks for the San Joaquin valley. Although this may be a benefit for the almond crop as good weather favors pollination by bees (and we were short on bees in 2013), we do need the rain/snow. With sunny and 70 degree days, I have received a few questions regarding fungicide sprays. Q: Do I need to spray for brown rot, shot-hole, and jacket rot?

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David Doll3 CommentsFebruary 9, 2012Diseases

Bloom Time Diseases and Control

Almond orchards are usually treated once or more during bloom for prevention of fungal diseases. These diseases include Brown Rot, Jacket Rot, Shot-hole, and Anthracnose. Flowers, flower parts, and young nuts are susceptible to infection, and often serve as the primary point infection for these diseases. Lack of properly timed sprays can provide the opportunity for a large amount of Brown rot infection of an almondblossom. The grey “fuzz” is the sporesproduced by the fungus.   infections. These epidemics create lingering disease issues which will cause orchard loss for the present and future cropping years. Brown rot, Monilinia laxa, infects the petals, pistils, and stamens of the almond flower. Upon infection, it moves into the woodier tissues of the tree, killing branches and forming cankers. All varieties are susceptible to brown rot, but they vary in their degree of susceptibility. Butte, Mission, and Wood Colony are the most susceptible; Carmel, Sonora, Fritz, and Monterey are moderately susceptible, while Aldrich, Nonpareil, and Peerless are the least susceptible. Brown Rot Blossom blight is usually controlled with a pink bud and full bloom treatments. Many of UCCE trials indicate that the full bloom treatment is the most important. A third petal fall spray may be necessary in years favorable to disease, especially if bloom is strung out and the weather is wet and rainy. A good rule to follow is that no more than ten days should elapse between treatments in wet weather. Canker caused by brown rot within Butte. This canker serves as a restingstructure for the fungus. A few growers have indicated that they do not spray for brown rot. This may be possible if good conditions persist through bloom AND the varieties planted are not very susceptible to infection (i.e. Nonpareil). It is important to note that not spraying can lead

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David Doll10 CommentsApril 7, 2011Diseases

Brown Rot or Bacterial Blast?

I have had a few calls regarding blossom dieback within almond trees. In many orchards, especially in Northern Merced, I have seen dried, crispy blossoms still stuck to the tree. In some cases, this may be brown rot, but in a year where we had a cold snap during bloom, this could also be bacterial blast. How do we tell the difference? Figure 1: Brown rot blight of an almond blossom. Note the grayish brown fuzz found at the base of the blossom. Brown rot will kill blossoms and will often move into the spurs and branches on the tree. As temperatures warm up, cankers form on the wood which sometimes cause gumming. These cankers serve as an over-season resting place for the fungus. Even more obvious than cankers is the formation of light brown to gray fuzz on the jacket or at the base of the flower (Figure 1). This “fuzz” is the spores of the fungus. Bacterial blast is a blossom blight that is caused by the bacteria Pseudomonas syringe. This is the same bacteria that causes bacterial canker and bud drop. Found naturally all over the tree’s surface, this bacteria is an opportunistic pathogen, meaning it will not affect a healthy tree. When a tree is stressed from nematodes (particularly ring nematode), poor soil conditions, lack of nutrients, or an extreme frost event, this bacteria makes it way into the tree’s tissues through cracks and natural openings killing affected tissues (Figure 2). Figure 2: Bacterial Blast of almond blossoms. Photo courtesy of M. Moran.  To determine if the dead blossoms in your almond trees was from blast or brown rot, ask yourself these questions:1). Did I spray for brown rot this year?2). Am I seeing the dead blossoms across all my varieties?3). Are the trees stressed in some way

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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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