David Doll6 CommentsFebruary 6, 2019General, Horticulture

2019 Almond Bloom Considerations

Almond bloom is just around the corner. This “start” to the season is an important period for almond production as flowers require reasonable weather conditions for pollination, fertilization, and eventual fruit set to occur. With that in mind, below are a few considerations for this period. Rain or conditions favoring dew can increase the amount of disease. Pathogens affecting almond flowers are ubiquitous in the environment, and therefore the condition that influences infection are periods of leaf wetness. Fungicides should be applied to protect the flowers from rain-splashed spores and subsequent infections. Newer class fungicides can move into the upper cell layers of the flower and kill infections, but this “reach-back” potential only provides about 2-3 days of “cure” after a rain event. Start the spray program with fungicides that are most effective for blossom diseases, but provide limited protection for petal fall and spring-time diseases. This typically includes the FRAC groups 1 and 9. As bloom progresses into petal fall, other fungicides should be considered to manage anthracnose, green fruit rot, shot-hole, and scab. FRAC groups 3, 7, 11 or combinations of these products should be considered. Remember to rotate away from fungicide FRAC groups used in previous sprays. This will help reduce the formation of resistance within pathogens, increasing the “shelf life” of a fungicide. To assist with this, especially if rainy conditions are expected, consider utilizing a broad spectrum material at petal fall or shortly after this period to provide the ability to use strobilurins and DMIs (FRAC 11 and 3) for scab and rust control. Some good rotational, broad spectrum products include chlorothalinil (FRAC M5), Ziram (M3) or Captan (M4). Don’t forget about the bees. Honeybees are brought into the orchard to provide pollination services – a requirement for production for most California type almond varieties

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David Doll4 CommentsDecember 20, 2018Diseases

Pest Alert: Peach root-knot nematode found in Merced and Kern almond orchards in California

Written and provided by UC IPM. Link to the original article (click here). In brief: Peach root-knot nematode is newly discovered in California, but its current distribution is unknown. Peach root-knot nematode is capable of infecting most Prunus rootstocks currently used in almond and stone fruit production. Rootstocks resistant to previously detected root-knot nematodes may not be resistant to peach root-knot nematode. The California Department of Food and Agriculture rated this nematode as an A quarantine-actionable pest. Contact your local county agricultural commissioner’s office if you suspect you have peach root-knot nematode (uneven and poor tree growth, stunting, and root galls on resistant rootstocks). The peach root-knot nematode (Meloidogyne floridensis) was recently discovered in California and has the potential to infect many of California’s economically important crops. At the time of this writing, it is not clear how wide-spread this nematode is in California. The California Department of Food and Agriculture (CDFA) rated this nematode as an A quarantine-actionable pest. Since the early 1960s, the rootstock Nemaguard and others such as Marianna 2624 and Myrobalan 29C, have protected Prunus crops (almond and stone fruits) from attack by southern root-knot nematodes (M. arenaria, M. incognita, and M. javanica), which are common in California. In contrast, peach root-knot nematode is capable of infecting Nemaguard and peach-almond hybrids. Research in Florida has identified some differences in response among Prunus rootstocks, but peach root-knot nematode itself has variability that allows some populations of it to infect peach and peach-almond hybrids rootstocks that are currently used in California. A consortium of University of California (UC) Cooperative Extension, UC Riverside and CDFA is working with the county agricultural commissioners of the affected counties, the growers, respective crop consultants, and the Almond Board of California to mitigate the potential impacts of peach root-knot nematode. Emphasis will be

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David Doll27 CommentsDecember 13, 2018Horticulture

Pruning Almond Trees

Pruning recommendations vary by the farmer, consultant, and even the University researcher. Some advise to prune trees hard to regenerate growth (not so much in CA anymore), some suggest that only a few limbs be removed annually, while others advocate throwing away the pruning shears. With these differences in opinion, what is the proper way to prune a tree? Young Orchards: Research has shown that reduced pruning on younger trees can lead to larger, earlier yields. This is mostly due to increased canopy that is able to produce crop. Some research has found early benefits of leaving young trees unpruned, but have found that over time, these branches will split when the crop load begins to increase leading to yield loss. Hence, some structuring of first and second leaf trees is recommended to address tight branch angles and close proximity of scaffolds, which leads to included wood and weak branches. Scaffold selection on young trees should be based on growing conditions. There is no set number that is ideal, and a farm level decision should take into account tree vigor, spacing and management practices. Heading the trees higher at planting (42” or higher) will provide more opportunity to select scaffolds, but will increase pruning time. Heading the trees too short may lead to issues with shaker head placement at maturity, leading to more bark damage. After the first year of growth, select scaffolds with distance in between and avoid scaffolds on the same plane and height of the trunk of the tree. By spacing the scaffolds vertically and around the tree, the growing limbs will be better attached, leading to less breakage. Remove steep angled limbs as these are often weaker. Limbs with a 45-60 degree angle are ideal. Avoid hard heading cuts as cutting the tree back too hard

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David Doll4 CommentsDecember 5, 2018Horticulture

Pruning: The Basics

Pruning is the practice of removing unwanted branches from the tree. Pruning can be broadly categorized to two types of cuts: heading and thinning. Heading cuts remove the terminal bud from the limb. This removes the “control center” and creates a varied response depending on the tree growth stage. Thinning cuts remove an entire limb is removed at a specified junction. This, as long as it is made in a position of low light, will often lead to little regrowth, regardless of when the cut was made. When making heading cuts, the time of the year matters. Dormant heading cuts often lead to an increase in vegetative growth the following spring. They are sometimes considered “invigorating cuts,” and can also be employed to redirect growth of a limb. In-season heading cuts will slow growth and are considered de-invigorating. These cuts slow canopy development as the tree has to redevelop the vegetative buds to push new growth. If timed appropriately, in-season heading cuts can lead to thickening of limbs and reduced breakage from wind and crop. Regardless of when they are made, heading cuts create branching. The growth response from a dormant heading cut depends on “how hard” the tree was cut back. The more proximal the cut (towards the trunk of the tree), the more vigorous the growth response. These growth responses originate out of epicormic buds, or buds that lay dormant within the wood of the tree. When these buds push, they grow without regulation and have very long internodal distances. This leads to very rapid, vertical growth that often has few fruiting positions. Thinning cuts can be made any time of the year. These types of cuts remove entire limbs and are commonly used to remove limbs from the lower canopy. Too many thinning cuts, however, can increase

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David Doll34 CommentsNovember 8, 2018General

Job Transition: Departure from UC Cooperative Extension

Dear friends and colleagues, For the past ten years, I have worked within Merced County focusing on tree nut production within California.  Much of  the effort was focused on extending relevant research based practices to industry members within California and conducting research that would help solve problems within the region. Over the years, my research program within the County has been broad – with projects on maximizing water application, managing replant problems within almonds, and a variety of smaller projects within horticultural, disease, and general agronomy. All of these plots were conducted within farmers fields, in which I am grateful for the local collaboration. Recently, I have decided to take a position within farm development and leave my position within extension.  This role will start in mid-November and will be responsible for developing a diversified specialty crop farm from the ground up. My new home base will be Evora, Portugal, which is about an two hours outside of Lisbon. As one could imagine, this was a difficult decision for me -the hardest decision I have made in my life. I have been blessed with wonderful colleagues and farmers, all whom have become friends over the past 10+ years. I will miss the interactions that we had through interactions within the County and at Industry event. With this departure, I still hope to assist the industry. I plan to continue “The Almond Doctor” to provide insight to a variety of aspects of almond production.  I would imagine that topics may have a different tone, and a redesign is planned. Regardless, I look forward to continuing the effort within this platform and hope it will provide assistance for the future. Thank you for you understanding through this period of transition. I look forward to seeing all of you at the various industry

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Cameron Zuber2 CommentsSeptember 16, 2018Field Notes, General, Irrigation

Field Note: Securing Irrigation Tubing

While conducting surveys across Merced County, I have noticed diverse ways growers secure the ends of irrigation tubing.  Many are attached using some type of stake made of wood or PVC in which the tubing is tied. Other orchards have the lines wrapped around a tree and used as an anchor for the line. Finally, some of them are staked directly into the ground. Irrigation tubing moves because of expansion and contraction of the plastic caused by temperature changes, as well as, from the water and air moving through the irrigation system. Securing the tubing creates tension that helps prevent the tubing from moving. These keeps the emitters and microsprinkers in place which helps maintain good irrigation efficiency. There are a few problems with securing the tubes. The first is the added cost and time to first secure the tubing and then maintain how the tubing was secured. Secondly, the lines may contract after fixing, which can pull them off the riser. Finally, the lines, if wrapped too tight, can cut into and girdle the tree. All of these are preventable. If you do choose to secure the end of your irrigation tubing, below are some considerations to take into account: Leave some slack in the tubing: Due to changes in temperature, plastic tubing expands and contracts. When tightly secured tubing contracts, coupling points may become undone (e.g., at the riser) or may cause the plastic in the tubing to stretch, creating weak points that may eventually break. Be wary of using trees to secure tubing: While this may cut down on supply costs, make sure it does not begin to girdle the tree. Do it right: Since you are taking the time (and money) to secure your tubing, be sure to do it right. There is a lot of power

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David Doll0 commentsSeptember 13, 2018Nutrient

Postharvest Nitrogen Management 2018

Many operations often apply nitrogen postharvest. Application rates vary from orchard to orchard, but typically I hear applications between 30 and 50 lbs/acre. This nitrogen is used to rebuild the nitrogen reserves within the tree and help with a variety of tree processes. Being applied late in the season, however, it is susceptible to leaching from over-irrigation and early rains. While it is critical to make sure there is nitrogen available for the tree, postharvest nitrogen budgets should be evaluated to determine if they are too high or not needed. Work at UC Davis has indicated that 15-20% of the nitrogen demand occurs from harvest through the post-harvest period. This suggests that somewhere between 20-30 lbs of nitrogen is utilized during this period, which could be sourced from residual nitrate in the soil or post-harvest applications. A further breakdown of the uptake curve shows that less than 8% of the annual need occurs after September, suggesting the importance of timeliness in application (Figure 1). Applications can begin when the abscission layer begins to form on the later harvesting varieties, but consider lowering rates to reduce the risk of hullrot flare ups (e.g. apply 10-15 lbs/acre instead of 25-30 lbs/acre). Applications of nitrogen in the post-harvest tend to be relatively inefficient due to several factors, including tree defoliation, leaching by early rains or long irrigations, shorter days and lower water use. This suggests that more nitrogen may be needed to achieve a 20-30 lb uptake, but studies in Kern County failed to see a response from applications greater than 50 lbs/acre of nitrogen applied after Nonpareil harvest (mid-August). Rates should not exceed this amount and applications made in September and October should be significantly reduced. Mid-July leaf nitrogen and residual soil nitrate should be taken into consideration when determining the amount.

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David Doll4 CommentsJune 22, 2018Diseases

Alkaline treatments have been shown to reduce hull rot

Recent research has found that alkalizing treatments applied at hull split are able to reduce the severity of hull rot caused by Rhizopus stolonifer. Over the past two years, work by Dr. Jim Adaskaveg and colleagues out of UC Riverside has repeatedly shown that several products reduce hull rot incidence. These products included dipotassium phosphate (applied as the product diKaP) applied at 48 ozs/acre, calcium hydroxide applied at 320 ozs/acre, and Cinetis applied at 24 fl. ozs/acre. A single application of each of these products made at 5% hullsplit was shown to be as effective as several fungicide combinations and reduced hull rot strikes by over 75% in comparison to the untreated control. Multiple applications, with one made at early suture split (traditional first navel orangeworm (NOW) timings), did not seem to reduce strikes further. The cause of the reduction in strikes is unknown. It doesnt appear to have a fungicidal effect on the fungus as often the fungus is present within the hulls. The current thought is that these products neutralize the fumaric acid that is produced by this fungus (this is the acid responsible for limb death).  It could also be due to an increase in tolerance to the toxin from the foliar product. Work is ongoing. With these products, timing is key. Apply around 5-10% hull-split. Since these products may be tank mixed with NOW products as well as other fungicides, confirm compatibility by running a jar test. If struggling in managing hull rot, consider trying these products on a selected blocks to see if they provide any reduction in observed damage. Just remember to leave an area untreated in order to determine treatment effectiveness.  Finally, keep in mind that the use of these type of products for hull-rot enters the “grey world” of registration.  Follow appropriate

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David Doll0 commentsJune 15, 2018Irrigation

Summer Irrigation: Considerations for Deficit Irrigation

Summer irrigation is challenging. Water use of mature almond trees is the highest of the season, with an average evapotranspiration being around 2.00 acre inches of water use per week during June and July for most of the San Joaquin valley. This doesn’t consider distribution uniformity problems as well as any high heat events that may occur, which may require increased water applications. During this period, it is common to see stressed trees. This is frequently due to the lack of or improper calculation of evapotranspiration (ETc) leading to under-irrigation. It may also be due to an under-performing irrigation system leading to poor distribution uniformity, in which some areas are getting over-irrigated while others are under-irrigated. Lastly, and sometimes surprisingly, poorly designed systems are commonly observed which aren’t able to meet the tree’s demand for the water in the summer.  This is due to miscalculation or variable well/pump flows, too low of application which requires long pump times, or general poor design that limits water flows (i.e. reduced pipe sizes to save money). Some stress during this period is okay. Mild water stress that occurs at the onset of hull-split has been shown to increase the uniformity (or ‘evenness’) of hull-split. Sometimes, especially in fine textured soils with high water holding capacities, this application of deficit irrigation can be applied earlier in June to draw down levels of stored soil moisture. In these cases, careful monitoring of tree stress through the use of a pressure chamber should occur. Water reductions should start in range of a 10-20% reduction. When trees reach a mid-day stem water potential (SWP) of 2-3 bars more negative than baseline, near-to-full irrigation should resume to reduce tree stress. As hull-split begins (~1% hullsplit, or when blanks split) AND there is a desire to reduce hull-rot, water

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David Doll3 CommentsApril 30, 2018Horticulture

2018 Almond Frost Event – What was learned

Field note written by Allen Vizcarra, Staff Researcher for UC Cooperative Extension, Merced County Almond frost damage begins when temperatures in orchards drop below approximately 28 °F, but the exact temperature depends on variety. There are a few but important practices to mitigate frost damage in orchards. Common practices include running irrigation water, mowing vegetation, and increasing air flow to the orchard (e.g., using fans to mix cold and warmer air). Implementing any or all these strategies could be just enough to increase the temperature by 1 or 2 °F, which can be enough to avoid or mitigate frost damage. Almond sensitivity to cold temperatures progressively increases from buds to small nuts, emphasizing the concern for cold temperatures during and after bloom. This past year, we observed survivability of almonds within orchards that were colder than the critical temperatures. This could be due to an increase in flower set of the remaining flower buds that opened after the freeze event. It could also be due to improper estimation of the cold temperature thresholds that we use as guidance. Finally, and more than likely, the varieties commonly planted within the field may be more tolerant to cold temperatures than we thought. Many of these were not ever evaluated for cold sensitivity. A recent observation near Chowchilla, CA in an orchard using micro sprinklers was the formation of icicles hanging from the lower canopy. There are always questions regarding if this is good or bad. The answer is a “it depends,” but generally it is better for the flowers in the upper canopy than the ones that are covered in ice. The icicles formed when irrigation water hit parts of the canopy by either unleveled sprinkler (i.e., spray not orientated perpendicular to the ground) or from a high angled spray pattern. Water

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