David Doll0 commentsFebruary 16, 2010Horticulture

Checking Thermometers to Monitor Frost Temperatures

By: Maxwell Norton (UCCE Merced) During frost season it is important to precisely know how cold it gets in various parts of your orchard or vineyard. Affordable minimum recording thermometers are available through farm stores and are usually pretty accurate but you need to check them yourself every year because they can “drift” up or down over time. The “U” shaped minimum-maximum recording thermometers are usually accurate at one end or the other but rarely both. Don’t use a “freebee” or a decorative thermometer. Fill a plastic bucket up with ice. Add enough cold water to make a slurry. Shake the bucket gently so the slurry stays loose. Insert the thermometers into the ice & water mixture so that about 2/3 of the thermometer is submerged. If it is an electronic sensor and it is waterproof, make sure it is completely submerged. Electronic devices may have a separate procedure for calibrating – check the instructions or their web site. Let the thermometers sit for twenty minutes. Pull the thermometers out one by one and immediately note the temperature. In a mixture of water and ice, the temperature should be 32F. If not, mark a correction factor on the thermometer. If it is more than 2-3 degrees off, you probably should not use it for something as critical as frost management. Thermometers should be placed in the low spots in the field that get the coolest. They should be away from and preferably up-wind from buildings, blacktop, or anything that might radiate heat at night. The thermometer should be about four feet off the ground and not be exposed to the sky – a simple “shelter” consisting of a board to attach the thermometer to with a cover extending 6-8 inches over the top works. Position the thermometer horizontally with the

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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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David Doll16 CommentsJune 22, 2009Horticulture

The Seasonal Patterns of Almond Production

When reviewing previous posts of this blog, I realized that not much information has been provided about the general biology of the almond tree. To cover this area, I decided to focus on the seasonal cycle of almond trees. In general, the season progresses in the following pattern: Dormant,Delayed Dormant, Bloom, Post-Bloom, Fruit Development, Harvest, and Post Harvest. Each period will be broken down and discussed. Dormant:As the temperatures from the late fall continue to drop, the tree enters a period of rest that lasts through December/Early January. At this time, the tree has dropped all of its leaves naturally or through an application of zinc, and is maintaining a low level of water use and starch consumption. This “low” flow of starch through the tree is needed as the catabolic breakdown of starch to sugar prevents the sap from freezing. This is, of course, only if the tree was able to develop enough starch reserves in the previous fall. In the rare occasion of low starch reserves, cold damage can occur leading to canopy and scaffold loss. Picture 1: A dormant spur. The cold temperatures that the tree is exposed to at this time helps with the development of the fruit buds. The tree requires a certain amount of moisture and chilling hours to come out of dormancy. Once the chilling hour requirement has been met, bud grown will begin with warmer temperatures. Chill hours are dependent upon the variety,but almonds generally need between 500 and 600 chill hours. In general, chill hours are the number of hours between the temperatures of 32-45 degrees Fahrenheit. Winter hours above 60 degrees are subtracted from the totals. Delayed Dormant:In late January/early February the tree begins to push a flush of fine feeder roots. These roots provide moisture and nutrients for the

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