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 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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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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