David Doll7 CommentsDecember 21, 2009Nutrient

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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David Doll4 CommentsDecember 15, 2009Diseases

Inquiries about Bacterial Canker on Almond

This week I have had a few questions regarding post harvest treatments for Bacterial Canker of almond. I thought it would be a good idea to use these questions as the theme for this weeks post. What is bacterial canker?Bacterial canker is commonly found on Prunus species (Peach, cherry, apricot, plum, almond, etc.). Caused by Pseudomonas syringe, a common surface inhabiting bacteria, the disease is often observed in the spring. Symptoms include limb dieback with rough, irregular cankers (Figure 1). Cankers do not extend into the soil and a very unique smell is present. In some cases, cankers do not form, but a “sour sap” stage occurs. This stage is characterized by brown inner bark with a distinctive fermentive, sour smell – hence the name. Generally, almond trees in the 2nd through 5th leaf are affected. Figure 1: Almond tree killed by bacterial canker. Note that the canker has an irregular shape and does not extend into the soil. How does bacterial canker spread?Pseudomonas syringe survives on plant surfaces and is spread by splashing rain. The bacteria is found throughout the entire orchard and is impossible to eradicate. The disease commonly occurs in the spring during periods of mild temperatures and high humidity. It does not spread like other diseases, but is common on trees that are stressed. Therefore, soils that have poor water/nutrient holding capacity (i.e. sand), have been replanted with several generations of Prunus sp. orchards, and have the presence of ring nematode are prone to this disease. Figure 2: Photo of an almond with a scaffold infected with bacterial canker. Note the irregular margin of the canker.What can I do to prevent the problem?In soils that have exhibited the disease, pre-plant fumigation with Telone or Methyl Bromide (if it is still available) provides the ability for the

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David Doll5 CommentsDecember 7, 2009Nutrient

Potassium Applications in Almonds

Having a major role in many plant processes, potassium promotes root growth, increases kernel/fruit size, and provides key metabolic features that include the formation of starch, translocation of sugars, stomata regulation, and the formation of xylem vessels. In general, plants deficient in potassium tend to have slow growth, with small, pale leaves. Trees that are severely deficient may have necrotic tips and margins. In many cases, the leaf tip curls upwards in a common symptom that is named the “Vikings Prow” (Figure 1). Since Potassium plays a large role in tree health, it is important to maintain proper levels of the nutrient within the tree. A critical leaf value of 1.4% has been established by the University of California and current research has suggested that levels above this value do not increase yields. Recent field studies by Roger Duncan (UCCE Stanislaus) have demonstrated that leaf potassium levels in excess of the 1.4-1.6% range did not increase yield. Through the study, leaf levels between 1.4-1.6% gave the best yield results, with yield decreasing when potassium levels were below this level. Leaf potassium levels higher than this range did not increase yield, and may actually reduce yields if applied in excess. Potassium usage by the almond crop is high. Upon harvesting the hulls and kernals, potassium is removed from the orchard. Studies by Dr. Patrick Brown (UC Davis), have shown that 76 pounds of potassium (92 lbs of K2O) are removed from the orchard for every 1000 pounds of kernals harvested. From nutrient analysis of the fruit parts, 70-80% of the potassium removed by the harvest is within the hull, while the rest is within the shell and kernel. Even though a large amount of potassium is used by the almond crop, it doesn’t always mean that large applications of potassium are needed

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David Doll3 CommentsNovember 30, 2009Diseases

Pruning Wound Cankers Found in Almond Trees

Making pruning cuts on almond trees is risky business. Every cut provides the opportunity for fungal/bacterial pathogens to enter the tree (Think: a cut on you hand can allow bacteria to enter). Once the pathogens enter the tree and successfully colonize, poor tree performance and shortened orchard life can be expected. Figure 1: Fungal canker associated with a pruning wound on a young tree. Upon bark removal, canker growth and damage is evident. Fungi are the most commonly found pathogens invading tree wounds. In figure 1, a large pruning cut was made on a super-vigorous first leaf almond. The pruning wound became infected with the fungi Eutypa which grew through the tree causing a large canker. This canker did not become noticeable until the third leaf. Upon bark removal, it is clear that the canker grows outward from the point of origin. As the canker continues to grow, it has the ability to kill branches by girdling (Figure 2), weaken scaffolds which then break (Figure 3), and/or killing the tree by girdling the trunk (Figure 4). Botryosphaeria is another fungi that may cause this problem. Figure 2: Scaffold killed by fungal canker girdling the vascular tissues of the branch. Figure 3: Scaffold split caused by weakening of crotch angle by invading fungi. Figure 4: Tree killed by wood fungal canker girdling the vascular tissue of the tree trunk. Bark removal shows the advancement of the canker. Irregardless of the possible infection by fungi, trees need to be pruned to shape (young trees), remove unwanted branches, and remove dead/diseased tissue. Knowing this, how can we prune the tree and reduce the chance of fungal infection? Most fungi require moisture/high humidity/rain event to produce spores. These spores are usually transferred by wind-blown rain. The “window of opportunity” for these fungi to infect

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David Doll3 CommentsNovember 10, 2009Diseases

Replant Disease of Almond

Written By Greg Browne, USDA-ARS UC Davis When orchards are replaced, growth and productivity of the succeeding generations of trees are often suppressed by “replant problems” unless precautions are taken. Replant problems can result from interacting physical, chemical, and biological factors, but the biological aspects usually dominate. Growers can minimize physical and chemical contributions to replant problems by pre-plant ripping and other site remediation practices and amendments to insure good soil water drainage, good soil structure, and optimal soil chemical properties (e.g. pH, soil extract electrical conductivity, etc.). Of course, appropriate soil tests are needed to evaluate the latter properties. Dealing with biological contributions to replant problems should also start with some homework—sampling for nematodes. Although plant parasitic nematodes (ring, lesion, and, on some rootstocks, root knot nematodes) probably contribute to replant problems in less than one third of California’s replanted almond and stone fruit orchards (rough estimate), it is important to sample your soil to check for them before replanting. Root damage caused by the ring nematode in sandy soils predisposes almond and other stone fruit trees to bacterial canker disease. In addition, although not common at most sites, Phytophthora species, Armillaria mellea, and Verticillium dahliae infest some orchard soils and can cause tree stunting, decline, and death in young replanted orchards as well as in established ones. It is difficult to detect and assess populations of these pathogens by soil sampling, and therefore a history of disease caused by them in the previous orchard tends to be the best predictor of future replant problems they may incite. Although it varies in severity, the most common replant problem is Prunus replant disease (PRD). In our experience, it occurs nearly universally in replanted almond and stone fruit orchards in California unless precautions are taken. Figure 1: Almond trees affected by

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David Doll0 commentsNovember 2, 2009Weeds

Fall survey for problematic weeds

Written by David Doll, UCCE Merced CountyMonitoring weeds in the fall provides the ability to evaluate the current year’s weed control program. By surveying the orchard for areas of weed species that escaped control, control practices can be adjusted to control these weeds in the following year. Fall monitoring also provides the ability to identify emerging winter species and allow for the selection of a pre-emergent herbicide to control spring weeds. (Note: Pre-emergent herbicides are usually applied at a later date – December-February). Surveying for weeds is relatively simple. After the first rains look for annual weeds in the tree rows to check the effectiveness of any previous pre-emergence herbicide applications. Check the ground cover in the row middles for any perennial seedlings. Record weed infestations and use a map to show areas of escaped weeds. With the emergence of herbicide resistant weeds in almond orchards (Hairy Fleabane, Pigweed, Horseweed, etc.) control of escaped weeds is critical to an affordable weed management program. For example, controlling glyphosate resistant fleabane with spot treatments of Rely/Gromoxone tank mix that has been found on 3 acres of the orchard block is more affordable than trying to control it over the entire 40 acre block. Only by monitoring can the areas infested by escaped weeds can be identified. It is important to use a different chemistry and address these escaped weeds BEFORE they become to big or go to seed. Below are some pictures of common weeds to help in identification:Figure 1: Bermudagrass (Cynodon dactylon). Vigorous spring- and winter-growing perennial. Frequently becomes a problem in mowed orchards. Very competitive for moisture and nutrients. Spot treat with postemergents. Figure 2: Dallisgrass (Paspalum dilatatum). Perennial commonly found in orchards. Seedlings in spring and summer. Tends to become dominant in mowed areas and standing water. Figure 3:

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David Doll2 CommentsOctober 27, 2009Diseases

Almond Tree Blow-Over Problems

Written by Bill Krueger, UCCE Glenn County Periodically fall winter or spring storms with associated high winds and saturated soil conditions result in high tree losses. As an example, a March 1995 a storm brought 6 inches of rain and wind gusts up to 100 mph to the Sacramento Valley and resulted in an estimated loss of 15,000 acres of almonds worth $210 million. More recently a storm in January of 2008 with wind gusts in up to 70 mph resulted in tree losses of greater than 30% in some orchards. When trees fall over their failure can usually be classified as windthrows or wood decay related. Windthrow is when trees with sound healthy roots are uprooted as a result of strong winds and wet soil conditions. Wood decay related failures are the result of infection from wood decay fungi, which consume the lignin in the cell walls of the heartwood. Eventually these trees fall, often in wind storms. Wood decay fungi are secondary pathogens and are not capable of penetrating intact plant membranes and must rely on some type of injury to gain access. Survey work conducted by Joe Connell, Butte County Farm Advisor and Jim Adaskaveg, UC Plant Pathologist following the March 1995 storm revealed the following. Generally, as trees aged tree losses increased. Windthrow was an important factor in young orchards (Fig.1). As orchards matured wood decay became more dominant. Wood decay accounted for approximately 90 % of the tree loss in mature orchards. Of 394 downed trees evaluated: 77% had wood decay and 81% had crown gall. Crown galls function as sites of entry for wood decay fungi.Generally almonds on Marianna 2624 suffered lower losses than peach rooted trees. The exceptions included orchards in flooded areas with softened soil and unpruned orchards with dense canopies. Generally

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David Doll2 CommentsOctober 19, 2009Diseases

Sampling for Plant Parasitic Nematodes

Many growers are facing the question of replanting orchard blocks. This aspect of orchard maintenance is critical and essential in maintaining an orchard business. Outside of the general tree removal, soil and ground preparation, there are 3 key biological replant problems that must be taken in consideration when replanting. These include plant parasitic nematodes, aggressive soil pathogens and pests, and replant disease of almond. This blog will focus on the first mentioned aspect of replant problems: nematode sampling and nematode control. In almond production, there are three main parasitic nematodes that are of concern – Ring, Rootknot, and Lesion. Depending upon your soil type, planted rootstock, and previous cropping history, the populations of these nematodes can vary within the soil. It is important to keep in mind that plant parasitic nematode populations are directly related to tree production – in other words, the higher the number present, the more tree damage to expect. A previous blog describes the affect of nematodes on tree growth. Orchard Sampling to Determine Nematode Populations. To determine nematode populations, soil samples collected from the root zone area of a tree should be sent off to a laboratory for processing. In collecting samples, the following procedure should be used: 1. By using a soil map, identify soil texture changes within the orchard block, 2. Time the sampling to occur after the year of cover cropping or fallow period – if one occurred, 3. Attempt to sample from different soil textures and areas of previous tree performance. A good sampling strategy for a 40 acre block can be seen in figure 1. Please note the sampling in different soil textures and random samples throughout the field, 4. Use a soil tube and sample the 4″-16″ depth of the profile – this is the area of most active

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David Doll1 CommentOctober 12, 2009Horticulture

Dealing with rain at harvest

A rain at harvest can be expensive – damage to the crop reduces the quality and premiums received from the huller, increase harvest costs reduce profit, and the use of forced air driers are costly. With rain imminent, it is important to keep in mind that practices should be employed to speed the drying of crop, whether it is in the tree or on the ground. The following guidelines may provide some help during a rain event during harvest. If rain is forecasted, do not shake trees as almonds will dry more quickly when hanging on the tree due to increased air circulation. If nuts are already on the ground, blow them away from trees but not into windrows or piles. Doing this will help prevent the nuts from sticking in the mud within the tree row strip. Once the nuts are stuck in the mud, it is difficult to move them away from the trees. Once the rain event has completed, rake the almonds frequently, turning them until they are thoroughly dry. If they are already windrowed, run them through a pickup machine and let the nuts fall out of the back. This will help turn the windrow nuts, increasing air contact, and will help remove wet debris from the pile. A table developed by Larry Reinhart (North State Hulling Company) is provided below to serve as a further guide – especially if showers or high humidity persists. Table 1: Prescribed actions for almond harvest involving a rain event. Information sourced from Chapter 35 of the Almond Production Manual:Connell, J.H., G.S. Sibbett, J.M. Labavitch, and M.W. Freeman. 1996. Chapter 35: Preparing for Harvest. Almond Production Manual. University of California, Division of Agriculture and Natural Resources. Publication 3364. Oakland, CA.

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David Doll1 CommentSeptember 28, 2009Diseases

Phytophthora Root and Crown Rot of Walnut and Almond

Root and crown rot of fruit and nut trees have caused major losses within orchards around the world. First reported in California in 1912, Phytophthora, which means “Plant Destroyer” in latin, causes root and crown rot throughout the San Joaquin and Sacramento valley. The problem tends to be more severe in areas of clay to clay-loam series soils, which can be attributed to the higher water holding capacity and poor drainage of these soils in comparison to sandier soils. The effect of Phytophthora spp. on root systems is often not noticed until the above ground parts of the tree show symptoms. Symptoms of Phytophthora damage are usually observed by poor tree vigor, loss of scaffold branches, and gumming or bleeding found around the tree trunk. Orchards affected by Phytophthora crown rot can suffer tree loss quickly, especially during the spring when winter-infected trees collapse during the first hot spell and during periods of high heat in which over-irrigation easily occurs. This is in contrast to tree loss that is attributed to root rot. In this case, by the time most growers recognize the symptoms, several trees are in a declining state due to a long period of infection (several years). Careful observance of the orchard can reveal problems and warrant remediation before the manifestation of severe orchard losses. Figure 1: Overall view of a walnut tree with Phytophthora. Note the collapse of the tree from top to bottom. As the disease infects the roots or crown, flow of water to the highest branches is compromised, with upper branch dieback being the first above ground symptom. In the orchard, symptoms of crown rot usually include cankers that are centered at the crown or lower part of the trunk. Removal of bark in affected areas will reveal brown or black sap-wood that

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