Nitrogen Content in a Gallon of UAN-32

I have been emailed a few questions in regards to calculating the amount of nitrogen in a gallon of Urea Ammonium Nitrate (UN-32 or UAN-32). Since UN-32 is widely used to fertilize/fertigate almonds, it is necessary to know how much is being applied per application. 1 gallon of UN-32 weighs 11.02 pounds. 32% of the weight is nitrogen – hence the “32.” This roughly equals 3.4 pounds of nitrogen per gallon, or 55 ounces. So, following the guidelines suggested by Brent Holtz (UCCE San Joaquin),when fertigating 2nd leaf trees with UN-32, at 110 trees/acre, no more than 4 gallons should be used in a single application. I hope this helps.

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Drift Management to Avoid Herbicide Damage

Written by Kurt Hembree (UCCE Fresno County) Reducing spray drift is necessary to prevent crop injury, both within the field being treated and off-site. Environmental conditions (air temperature inversions, wind velocity, etc.), applicator awareness, type of spray equipment, nozzle selection, spray boom operating pressure, water volume discharge, and other factors affect the degree of drift that may occur during any application. While spray shields do not guarantee drift will not occur, they can greatly minimize the risk of drift, especially in open fields or where young vineyard and orchard plantings are being treated. The following steps should be taken to minimize the risk of drift from ground sprayer equipment: 1. Don’t spray when it’s windy: Do not spray in winds above 6 – 10 mph. 2. Be cautious on calm days: Do not spray under dead calm conditions in early morning, evening, or the night. Calm conditions are often associated with temperature inversions which can result in long-distance spray drift (1 mile or more). Burning brush on calm days can give an indication on the presence of temperature inversions (refer to local regulations on restrictions for obtaining a burning permit). 3. Check the buffer zones: Refer to the product label to determine adequate buffer zones outside of the field treated. Do not spray if the wind is blowing towards a nearby sensitive crop, garden, waterway, or other sensitive area. 4. Use a shield: Consider equipping your sprayer with a protective shield. A number of designs are available that can reduce drift between 35 and 75%. Avoid spraying trunk-to-trunk with unshielded spray booms. 5. Use a spray drift retardant: Spray drift retardants are available that can be added to many products to help reduce off-target drift. 6. Check the formulation: Use amine formulations of 2,4-D when possible. Use special care when

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Orchard tasks to help prevent frost damage

A light frost event is predicted for Tuesday and Wednesday night. Last year, an unexpected frost event caused a lot of damage to almonds throughout the San Joaquin Valley. Today’s entry will focus on frost protection. Types of frost. There are two major types of frost events that occur throughout California. An advection frost occurs when a cold front moves into the region, displacing the warm air. These events are rare and will have temperatures dropping below freezing even though the it may windy. They are very difficult to protect against due to the rapid displacement of heat from the orchard. Radiation frosts are more common. They are characterized by clear skies, calm winds, and temperature inversions. These frost events occur due to the gradual loss of heat from the orchard. Almond Susceptibility to Frost. Generally speaking, the further the tree advances out of dormancy, the more sensitive to frost it becomes. A dormant tree is very tolerant to cold temperatures, while small nutlets are very sensitive to frost damage. At this point of the growing season – petal fall to early nutlet development – temperatures below 26F will cause significant to total loss of the almond crop, while temperatures above 28F will cause minimal damage to the crop. The small difference of 2F makes the difference, and is why frost prevention strategies can be used to reduce crop loss. Frost damage prevention.Assuming that the orchard has already been planted (Further information regarding site selection for frost prevention can be found in the UC Almond Production Manual), Growers can manage their soil moisture and ground cover to help reduce frost damage from a radiation frost event. Moisture within the soil retains heat. This heat is then radiated up into the trees during a cold night. Dry or cultivated soil usually

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Fungicides and Bee Health

I have had a lot of questions/concerns regarding bee health and bloom fungicides sprays. Even though bloom is nearing its end, I thought I would try and answer a few questions I have received – and finally had some time to research and formulate an answer to these questions. Do fungicides applied during bloom affect bee health?The short answer is “We don’t know.” Research has shown that fungicides that are applied around or at bloom do adhere to the pollen, and are brought back to the hive during the process of pollination. The fungicides then inhibit the growth of different fungi within the bee hive, decreasing the the microbial diversity of the bee’s food source. As of the Almond Board of California 2009 Research Proceedings, it is unknown whether or not the fungi affected benefit or harm the overall health of the hive. Which Fungicides are transported back to the hive?Researchers at the Carl Hayden Bee Research Center in Tuscon AZ found five commonly used fungicides in the bee bread (food source) of hives placed in almond orchards. These fungicides include Chlorothalonil, Cyprodinil, Fenbuconazole, Iprodione, Boscalid, and Pyraclostrobin. The amounts of fungicide appear to vary by orchard and timing of application – BUT – this data was only based on hives placed in three orchards with two or three samplings- for now. Also, it is not known which fungicides target which fungi, if they negatively affect bee health directly, and if they have a negative impact on the entire hive by reducing the quality of the food source. The research group headed by Dr. DeGrandi-Hoffman will be looking into these questions through this year. What about Pristine (Pyraclostrobin-Boscalid) applications?Essentially, we don’t know exactly how this fungicide affects fungal growth in the hive. In vitro studies from Dr. DeGrandi-Hoffman’s lab indicates

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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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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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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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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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Organic Weed Control in Almond Orchards

Weed control within organic blocks is more critical than in conventional blocks. Weedy orchards can compete for the high value organically certified nutrients, decreasing yields and/or increasing fertilizer input costs. Organic weed control methods are also not as effective and more costly than conventionally available materials. Therefore it is important for growers to use multiple strategies to reduce weeds to a level that is economically acceptable. This entry will focus on several methods available for organic almond production weed control. These methods may also be useful in conventional orchards that have multiple areas of herbicide resistant weeds. Mulches: Plastic or fabric mulches block light, preventing weed germination or growth. These materials are often placed in the row strip before planting. Upon planting, a hole is made at the planting location so that the tree can be planted. Placing the mulches post planting can also be done. These materials control most weeds effectively while they are still intact. Materials do degrade over time due to UV light and temperature. Weed seeds that land on top of the mulches can germinate and grow. These types of materials are expensive ($250-$300 treated acre) and post-use disposal can be problematic since they are currently are not able to be recycled. Organic mulches (straw, newspaper, wood chips) can be used for early season weed management, but often interfere with harvesting practices. Organic mulches are most effective when they are at least four inches thick. Use on non-bearing age trees may be feasible. Remember, these mulches MUST be organically certified to be used. Cultivation: This is the most widely used organic weed control method. Cultivation uproots and buries weeds. This tends to work better on smaller, shallow rooted weeds. Deep cultivation is not advisable since it can damage tree roots. Usually, a mix of a tractor

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Managing Resistant Weed Populations

Over the next couple of weeks, I will be presenting information regarding weed control in an orchard system. Since herbicide resistant weeds are becoming more prevalent in the San Joaquin Valley (think Hairy Fleabane, Horseweed/marestail), it is becoming more important for growers to utilize practices that reduce the chance of herbicide resistance. Herbicide resistance is defined as the inherited ability of a plant to survive and reproduce following an exposure to a dose of herbicide that would normally kill the wild type (Think: “We used to get good control of this weed with this herbicide…”). This is different than herbicide tolerance, which is the ability of a species to survive and reproduce a herbicide treatment with no implied selection or genetic manipulation that would make the plant tolerant (Think: “We’ve never gotten dependable control of this weed with this herbicide…”). Since 1980, cases of herbicide resistant weeds within California has increased from 0 to 21 reported cases. This is mainly due to the change in tillage and herbicide use practices within agriculture. In perennial crops, growers have shifted away from orchard tillage and have become more reliant on herbicide “burn downs” to control weeds in the tree rows. Glyphosate is one of the most widely used herbicides for this practice, and, until recently, has provided good control. The formation of herbicide resistant weeds is an evolutionary process that occurs due to the application of herbicides. Since most herbicides are reliant upon a single site mode of action, it only takes a minor mutation within the plants genome to become resistant. Furthermore, the high genetic diversity of weed populations provides the opportunity for weeds to contain a mutation, thus yielding an “escape.” Once the weed is unable to be controlled by the herbicide, it produces progeny that is also resistant. These

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