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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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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New pesticides are effective on Peach Twig borer in early sprays

Author: Franz Niederholzer, UC Farm Advisor Sutter-Yuba Counties Peach twig borers (PTB) are a key pest of almonds. Nuts damaged by PTB are preferred feeding sites of navel orangeworm (NOW). At a recent almond IPM meeting in the San Joaquin Valley, a leading independent PCA told the audience that a good NOW program included PTB control. Talk with your PCA and review reject sheets and moth traps to decide if PTB control is needed in your orchard. Dormant, delayed dormant, or bloom sprays (See this article about insecticides at bloom), with the proper pesticide, give effective PTB control when applied properly (every-row spraying and proper sprayer speed). Other effective timings include a spring or summer spray(s) timed using moth trapping data and degree days. Recently registered pesticides give excellent PTB control in research by Dr. Frank Zalom, UC Davis Entomology Department, in the Sutter/Yuba region (see table below). These materials are less toxic to operators and wild life, especially those that live in water. Consider these new materials as part of a PTB control program in your orchards. Organo-phosphate pesticides (Lorsban, diazinon, etc.) and pyrethroids (Asana, Warrior, Brigade, Baythroid, Mustang, etc.) are very effective on PTB, but can harm fish and other life in local streams if the pesticide moves to the water in drift or water runoff from rain or irrigation. Including a new pesticide in your PTB program in dormant to bloom also helps avoid pest resistance to organo-phosphates and/or pyrethroids.

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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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Making a Zinc Dormant Spray

Question came in this week regarding the decision on the timing of a zinc spray. When should I make a Zinc Spray?Research by UC Specialist Dr. Scott Johnson at the Kearney Agricultural Center has shown that a zinc foliar spray is the most effective when made during the post harvest period. Applications of zinc should be made to the tree around late October – early November. The idea is to have a leaves still on the tree when the application is made. Dr. Johnson has shown that a roughly 3% of the zinc applied is taken into the tree from a fall foliar spray, but this is dependant upon the source of zinc. Defoliation may occur after the application, but do not worry as sufficient zinc should have made its way into the plant tissues. Is making a dormant zinc application a bad idea?If a fall application of zinc was not made and the orchard is suspected to be deficient in zinc, making a dormant application of zinc will increase zinc tissue levels. The percentage of uptake is slightly less, around 2.0-2.8%, and it is harder to get a large amount of zinc into the tree. This is due to the fact that the shoots, buds, and bud scars only account for roughly 3% of the surface area of a peach/almond branch. Therefore the amount of spray landing on the tree surface is significantly less than when the leaves are still attached (Leaves make up the other 97% of the surface area). To counter this, higher rates should be used during the dormant period. What type of material should be used in a zinc spray?Dr. Scott Johnson’s (UC Specialist) work has shown that the “biggest bang” for your buck comes from Zinc Sulfate (high uptake, moderate phytotoxicity). There are other

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