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 Doll2 CommentsJanuary 23, 2012Diseases

Pruning Wound Cankers of First Leaf Almond

Figure 1: Fungal infection of a pruning wound that occurred during first leaf pruning on Padre Pruning wound cankers have been observed on all major varieties and are the most damaging to orchards. Cankers that develop on the primary (Figure 1) or secondary scaffolds (figure 2) of young trees will lead to the loss of these scaffolds and eventual tree death. Sometimes infection occurs within the wind cracks found in the base of the scaffolds. Removal of the infected scaffold may be possible, but all of the diseased wood must be removed or the infection will remain. To stave off infection, proper structuring and tying of trees to reduce wind breakage, and pruning when the weather forecast is clear, is advised. Delayed spring pruning or late fall pruning to avoid the rains may be necessary. Pruning cuts should not be cut flush with the tree, but rather be made outside of the branch collar as this increases the rate of healing. The varieties  Aldrich, Carmel, and Padre appear to be more susceptible than Nonpareil or Butte. This disease has been noted to have a high occurrence around rivers, sloughs, and other riparian areas. It is important to note that once the tree is infected, there are no fungicide or nutrient sprays that can cure this disease. Figure 2: Fungal infection of a pruning wound made on a secondary scaffold in Padre. Control strategies for these three diseases have been difficult to develop due to the complexity of the fungi’s lifecycle. Initial infection is thought to occur through airborne spores that move in to an orchard from a residual population. Recent research has shown that uninfected trees can harbor populations of these fungi. It is thought that the fungus has the ability to infect and survive on dead bark, remaining dormant until conducive conditions occur

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David Doll2 CommentsDecember 11, 2011Diseases, Insects

Dormant Spray Considerations for Almonds

Scab lesions on green wood of almond. Being one of the quieter times of the year, the dormant period is a prime time to assess orchard issues and begin applying strategies to reduce various diseases and insect pests. Surveying the orchard and sampling new growth and spurs can help identify problems of scab, San Jose Scale, Navel Orange Worm, and mites. If populations are high enough, dormant strategies can be applied to reduce the damage to the upcoming season’s crop. Scab. If a scab outbreak and the corresponding mid- to late-season defoliation were experienced this past year, a dormant/delayed dormant application of copper and oil should be considered. This spray is effective in reducing and delaying sporulation of scab twig lesions, thus reducing in-season disease incidence. It should be used in combination with properly timed bloom and petal fall sprays. Based on field observations, orchards with significant scab outbreaks in 2010 that followed the above recommendations had obvious suppression of the disease in 2011, and were able to keep the leaves on the trees until late November. Red Halos caused by San Jose Scale feeding/infestation in almond. Insect Pests. Spur samples should be selected throughout the orchard to determine the presence of San Jose Scale (SJS), European Red Mite (ERM), and Brown Almond Mite (BAM). Spurs should be pulled from a main scaffold with 100 spurs samples from the orchard. If 20% of the spurs selected are infested with scale, then a one-time oil application at 6-8 gallons per acre should be applied. If over 60% of the spurs are infested, the oil application should include an insect growth regulator that targets SJS. It is important to control SJS as high populations can kill spur wood, reducing crop load. Obvious signs of scale infestation include a red halo found on

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David Doll0 commentsOctober 12, 2011Diseases

Stockpile Management to Minimize Aflatoxin Potential

Written by Bob Curtis, Almond Board of CaliforniaRecent studies supported by the Almond Board show there are clearly stockpile moisture conditions under which Aspergillus can grow with resulting aflatoxin contamination. This work is being led by Bruce Lampinen (UC Davis Extension Specialist) and and Themis Michailides (Plant Pathologist, UC Kearney Agricultural Center). Current guidelines were reviewed at the 2010 Almond Industry Conference seminar “Harvesting Clean and Safe” with presentations made by UC Farm Advisor Joe Connell and Bruce Lampinen. Moisture Content, Stockpiling and AflatoxinStockpile Management to Minimize Aflatoxin PotentialRecent studies supported by the Almond Board show there are clearly stockpile moisture conditions under which Aspergillus can grow with resulting aflatoxin contamination. This work is being led by Bruce Lampinen (UC Davis Extension Specialist) and and Themis Michailides (Plant Pathologist, UC Kearney Agricultural Center). Current guidelines were reviewed at the 2010 Almond Industry Conference seminar “Harvesting Clean and Safe” with presentations made by UC Farm Advisor Joe Connell and Bruce Lampinen. Stockpiling at a “total fruit” (in-hull almond) moisture content greater than 7% is problematic. This leads to an rH of greater than 70% within the pile — which is the maximum rH for almond storage. Most critical is the outer portion of piles where there can be significant temperature fluctuation, condensation on tarps, and moisture accumulation. Of particular concern in these outer portions are the “green molds”, which include the Aspergillus mold that produces aflatoxin. This is not a uniform problem throughout high moisture content piles because the equilibrium rH within the piles comes to a steady state below maximum limits recommended for storage A practical guideline: Do not stockpile if either the hull moisture content exceeds 13% or the kernel moisture content exceeds 6%. Managing Piles Orientation and shape of pile both can play an important role in minimizing

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David Doll0 commentsAugust 26, 2011Diseases

Alternaria Found within Merced County

Relatively rare in the northern San Joaquin Valley, I was in an orchard today with Alternaria Leaf Spot. Caused by the pathogen Alternaria alternata, this disease usually appears by mid summer and causes defoliation. Significant problems with Alternaria have been observed in the southern San Joaquin Valley and northenr Sacramento Valley. In some of these orchards, resistance to strobilurins fungicides has occurred, which indicates the need to properly rotate fungicide chemistries when spraying to control this disease. Please see this UC Almond IPM page for more information. Here are some pictures to help you identify Alternaria leaf spot: Leaf symptoms of Alternaria on Carmel Another shot of Alternaria Leaf Spot on Carmel Leaf Lesion of Alternaria found on an almond leaf. Note the zonate appearance of the lesion and black specks – these are the identifying symptoms of this disease. Another photo showing the zonate appearance of the lesion.

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David Doll0 commentsAugust 20, 2011Diseases

Reports of Hull Rot

I have been getting a few calls regarding hull rot. I have covered this topic before (link to previous article), but some of the particular questions regarding the disease are answered below. What is Hull Rot?Hull rot is infection of the almond hull by two fungi, Rhizopus stolonifer (common bread mold), or Monilinia fructicola. These pathogens are common throughout the environment, and are, in this case, serving as opportunistic pathogens. Upon infection, they release toxins that are translocated into the fruiting wood, which kills the wood, causing crop loss. What do you mean by opportunistic pathogen?Once the hull splits, the perfect micro-climate for fungi is created. The hull is full of nutrients and water – the two things that fungi want from a host. Since the spores of these fungi are found throughout the air, they invade the newly split tissue, infecting, and completing their life cycle. By reducing the “home” for the fungi, we can reduce the number of hull rot strikes. These strategies include reducing the water and nutrient content of the hull. How can I prevent Hull Rot?Asking “How to prevent” is a good start. Prevention is the key to reducing hull rot strikes. Hull rot often affects high vigor orchards. Nitrogen should not be applied after kernel development is completed. This is typically the end of May, but this year it extended into mid-June. A slight to moderate water stress at the onset of hull-split should be applied. Applying both of these practices to the orchard has been shown in multiple research trials to reduce hull rot by 80-90%. Often times, this is all growers need to do to prevent severe hull rot issues. I tried those things, I still have hull rot!Severe outbreaks of hull rot have been observed. Last year, hull rot infections occurred in many orchards. I

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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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