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 Doll0 commentsJune 9, 2012Diseases

Summer Disease Control: Should I Spray Again?

This past week, rain showers hit across the state, extending as far south as the Madera/Fresno area. In the Merced area, rain was variable, with most reports indicating about a 0.5″ of rainfall.I have had a few questions regarding the the need for another fungicide spray for the summer diseases of Rust and Alternaria. The following conditions and considerations should be kept in mind when deciding the need for another spray: Orchard History. If defoliation occurred last year due to these pathogens, there is a good chance that the over-wintering inoculum levels are high, increasing the chance for an epidemic this year. This factor remains important even if sprays were applied earlier in the season. Conditions post rain event. The hours and days after the rain were windy and warm, which dries the orchard. These conditions helped reduce the duration of leaf wetness, and canopy humidity, creating an environment that would be less favorable for disease. Timing of last fungicide spray. If a fungicide was applied in late May due to a delay on the “May Spray,” there is a good chance that there is enough residual control of the material. Sprays of DMIs and strobilurins provide protection of covered tissue for 14-20 days in conditions without rain. If a fungicide hasn’t been applied since the late April/early May, a spray should be considered due to the lack of leaf protection. Any new growth that occurred since the last spray will not have adequate fungicide protection. Tolerance of disease. My perspective in managing foliar diseases is to achieve the goal of having active leaves present on the tree in late October. In other words, there can be some disease present on the trees, but the tree has not defoliated and still has the ability to photosynthesize. Many people have a different threshold, which usually

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David Doll0 commentsApril 27, 2012Diseases

Considering an Almond Rust Spray?

There have been a lot of inquiries in regards to the decision of making a fungicide application for almond rust. Rightfully so, as last year was a bad Rust year, and this year’s weather conditions are very similar. With that in mind, I would encourage people to consider a rust spray this year, especially since: 1. The severity of the rust problem last year was widespread, therefore inoculum is abundant; 2. Weather conditions have been mild and humid, conditions that favor fungal foliar pathogens; 3. Most people have not applied a fungicide in several weeks. Rust timings for almonds begins at five weeks post petal fall and carries into the summer. Most fungicides are effective on rust. Of note are the strobilurins and DMIs. Avoid Copper, Iprodione, Topsin-M, Rally, and Laredo as they shown the least amount of control in the last round of efficacy trials conducted by Dr. Jim Adaskaveg.  Sulfur and Microthiol can be used, but multiple applications are recommended (I.e. Now, Late May/early June). Common missteps I see in regards to rust control using fungicides: 1. Trying to split the scab and rust treatment – applying a fungicide at one timing for control of both diseases. This spray is usually applied at five weeks post petal fall and usually misses one of the foliar pathogens; 2. Wanting a free ride for the fungicide. This means that they wait until the spray for mites. In cool years, mite sprays are delayed, and  therefore the rust application is delayed as well. 3. Not understanding that sprays need to be made before symptoms are observed. Upon orchard infection, it is very difficult, if not impossible, to control a rust epidemic; 4. Expectations of no disease. In bad years, the goal should be to keep the leaves on the trees until late October/early November. Having some rust present

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David Doll2 CommentsMarch 16, 2012Diseases

Scab Spray Timing and Other Spring Disease Questions

Wet weather has found its way into the valley, with rain events predicted off-and-on for the next week to 10 days. I have had a few questions regarding fungicide applications. Chlorothalonil (i.e. Bravo) isn’t registered for jacket rot of almond? Should I tank mix in another fungicide to provide protection? Figure 1: Overwintering scab lesions on the green wood of almonds. That is correct – Almond jacket rot is not on the label for chlorothalonil. Therefore, if a recommendation is written for jacket rot, another labeled fungicide must be used. FYI – chlorothalonil is labeled for jacket rot of apricot, which is caused by the same pathogens (Botrytis cinerea, Sclerotinia sclerotiorum, Monilinia laxa,Monilinia fructicola). What is the best time to apply a fungicide for Scab? Scab (Cladosporium carphophilum) overwinters on twigs of almonds (Figure 1) and will re-infect new leaves shortly after leaf out. Control of this diseases has been documented with dormant applications, petal fall applications, and applications made 2-5 weeks after petal fall. Earlier post-petal fall applications (~2 weeks) provides more effective control than later applications. Figure 2: Scab lesions sporulating on an almond branch. Note the darkened circles within the lesion. Fungicides should be applied for protection when this is observed to prevent scab infection. Photo courtesy of the Almond Board of California. The timing of the fungicide application should be made when the overwintering scab lesions begins to sporulate (release spores into the orchard).  When sporulating, the lesions, which are found on the green twigs of the tree, will develop a dark ring (Figure 2). Providing protection of the leaves with fungicides at this point will help reduce/prevent scab infection of the almond trees. Is there any way of determining if we are going to have another bad year of rust or scab? Predicting disease epidemics is challenging. Basic epidemiology indicates

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David Doll2 CommentsFebruary 15, 2012Diseases

Managing and Preventing Fungicide Resistance

The use of FRAC numbers was created to help determine the mode of action of the varying fungicides. One class of fungicide may have differing active ingredients and be sold under several different trade names. For example, FRAC group 3 is sold as Bumper, Tilt, Elite, Indar, Laredo, and Quash. Regardless of the trade name or active ingredient, any one of these fungicides within a FRAC group kills the fungal pathogen the same way. In order to prevent fungicide resistant pathogens, back-to-back applications of any one FRAC group should be avoided. Figure 1: Application of a fungicide to control a foliar pathogen. The blue dot represents a resistant fungal colony to fungicide A. The formation of fungicide resistance by many pathogens is inevitable as it is basically a game of odds. Making an application of one fungicide kills the majority of the fungi in the environment that are susceptible to that particular fungicide. There are always a few colonies of the targeted fungi that “escape,” and have some degree of resistance to the chemistry (lets say odds of 1/10,000) (Figure 1). This may seem surprising, but this is due to the varying genes found within the same species of fungi (It is no different why you catch a cold, and your coworker remains healthy). Making a second application of the same chemistry provides the environment for the “escaped” population to continue to reproduce and colonize healthy tissues (Figure 2). Eventually, the “escaped” population will become the majority of the population (Figure 3), and attempts to control the pathogen by spraying the same fungicide over and over will not occur (Figure 4A). Figure 2: After fungicide A application, the resistant blue colony “escapes” and begins colonizing other healthy tissues, increasing in population. Employing resistant strategies such as fungicide rotation can delay resistance formation. By avoiding back-to-back

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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 Doll0 commentsFebruary 2, 2012Diseases

Chlorothalonil and Oil for Scab Control — To Late? Yes.

Figure 1: The effect of dormant treatments on the incidence of almond scab sporulation. Observations were made on May 3rd, 2011. Different letters indicate significant treatment differences at p<0.05. There has been quite a bit of talk about the use of Chlorothalonil and oil applied during dormant for Scab control. Although this treatment has shown to reduce overwintering scab populations and delay scab lesion sporulation (Figure 1), caution needs to be taken when considering application. This product needs to be applied when the tree is completely dormant. Once the tree starts to push and the buds begin to swell/green tissue appears at the tip (Figure 2), avoid using this spray treatment. Chlorothalonil mixed with oil applied to green tissue will kill the green tissue, explaining why this product is labeled for dormant use no later than December. Figure 2: Delayed dormant stage of an almond bud. Note the bud swell and exposed green tissues. If a dormant scab treatment is to be applied at this time (delayed dormant/bud swell), consider making an application of copper and oil. This treatment has also been shown to be quite effective (Figure 1), especially when used in combination with in-season scab sprays timed 2-5 weeks post petal fall.

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David Doll0 commentsAugust 12, 2011Diseases

Summer Foliar Disease Epidemics – Scab

Scab lesions found on almond twigs. I have scab all over my orchard. What can I do? Short answer – nothing. It is too late to expect control of the disease. Once the fungus infects the leaf and produces visible symptoms, that is a clear indication that the fungus has colonized the inside of the leaf. No fungicide completely penetrates the leaf surface, which makes it impossible to cure an infected leaf. Furthermore, spraying a fungicide upon seeing a disease epidemic will end up doing more harm than good. Since the fungus has completed it’s life cycle several times (Scab is a polycyclic disease), the population within the orchard is so high that making an application can lead to the selection of a fungicide resistant strain of scab. Scab lesions found on the underside of almond leaves. If every tree has scab, what can I expect? Defoliation. As the fungus colonizes the leaf, it begins producing spores which are the reproductive structures of the fungus. These spores are produced and move from an infected leaf to a healthy leaf. Upon complete colonization, the tree detects that the leaf is infected, forms an abscission layer which causes the leaf to fall from the tree. If enough leaves are infected on the tree, total defoliation can occur – and in most cases, is expected. Symptoms of scab observed on the top-side of almond leaves. What should I do? Since scab overwinters on the infected twigs in the form of lesions/fruiting bodies, population reduction is based upon controlling the disease present within the field, and coverage of susceptible tissues in the spring. Dormant applications of of copper and oil or chlorothalonil and oil have been shown to reduce summer populations of scab, and are recommended in orchards that have experienced leaf loss the previous summer/fall. Prophylactic sprays

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David Doll0 commentsAugust 5, 2011Diseases

Summer Foliar Disease Epidemics – Rust

I have received quite a few calls regarding rust and scab. Over the next few weeks, I am going to answer the commonly asked questions about these diseases and provide a management strategy to help reduce disease pressure for future years.In regards to a general overview of Rust, please see the following:Almond Leaf Rust – The Almond Doctor from April 10th, 2010,Almond Rust – UCIPM Website. I have rust all over my orchard. What can I do?Short answer – nothing. It is too late to expect control of the disease. Once the fungus infects the leaf and produces visible symptoms, that is a clear indication that the fungus has colonized the inside of the leaf. No fungicide completely penetrates the leaf surface, which makes it impossible to cure an infected leaf. Furthermore, spraying a fungicide upon seeing a disease epidemic will end up doing more harm than good. Since the fungus has completed it’s life cycle several times (Rust is a polycyclic disease), the population within the orchard is so high that making an application can lead to the selection of a fungicide resistant strain of rust. If every tree has rust, what can I expect?Defoliation. As the fungus colonizes the leaf, it begins producing spores which are the reproductive structures of the fungus. These spores are produced and move from an infected leaf to a healthy leaf. Upon complete colonization, the tree detects that the leaf is infected, forms an abscission layer which causes the leaf to fall from the tree. If enough leaves are infected on the tree, total defoliation can occur – and in most cases, is expected. What should I do?Since rust overwinters on the infected leaves in the form of teliospores (black spores found on the bottom of the leaves), it is important to destroy/remove all leaf

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David Doll0 commentsMay 14, 2011Diseases

Rain this weekend?

Although a late entry for the week, I figured I better address an issue that is facing many almond growers: a late spring rain storm. A rain event is predicted for Sunday with possible carry-over to Monday. I have received a few calls regarding the decision to spray fungicides for various foliar diseases. In many cases, making an application for a one day rain event is not warranted unless there is a persistent disease problem. Spray applications should be considered if there is a history of almond anthracnose, or in orchards with severe brown rot infestations. If sprays are made, try to use broad spectrum fungicides that target multiple pathways. Using these products will help reduce the formation of resistance. If you do not have a history of these diseases, I would hold off on making an application as the winds and warm weather will usually dry the almond leaves before a severe outbreak occurs. If rust is a concern, Dr. Adaskaveg from UC Riverside has shown that control of almond rust can be achieved even after initial symptom development. He has recommended sprays of sulfur or strobilurins and encourages growers to scout their orchards for the presence of the disease. This is great news since it provides growers with the ability to treat upon seeing an infection versus a prophylactic spray for a disease that may not occur. Keep this in mind as we enter late May and early June – rust symptoms begin to appear in these months.

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