David Doll0 commentsAugust 8, 2019Diseases, Field Notes

Field Note – Powdery Mildew of Almond

Written by Cameron Zuber, UCCE Merced County Some interesting almonds came into the office and, no, this is not a setup for a joke. In the middle of July, some almond fruit nuts from Le Grand, CA were brought into the Merced County UC Cooperative Extension office. There were various signs of possible pest damage and disease infection. These included black growth inside the hull indicating possible Rhizopus stolonifera fungus which may lead to hull rot; grayish-black spots indicating scab (Cladosporium carpophilum); and gumming which may indicate bacterial spot (Xanthomonas arboricola pv. Pruni), anthracnose (Colletotrichum gloeosporioides), or bug feeding. However, the greatest amount of damage were odd areas of russeting and cracking on the hull. After speaking with person who brought in the samples, there was not any indication of leaf or shoot die back near the nuts which starts to rule out hull rot and lab tests did not show any fungi that would cause hull rot. Lab test also showed some instances of almond scab growths, but none of these pest or disease symptoms were at a level to be extremely concerned about. Also, none have been shown to cause the odd cracking on the hull, so what was the cause, should you be worried about it, and how do you fix it? The cause was found through some digging and a lot of help from farm advisors and plant pathologists. It was determined that the cause was most likely a false powdery mildew (or powdery mildew-like) fungus of the Acremonium species. Normally these organisms live on dead or decaying organic matter (i.e., saprophytes), but do occasionally infect plant material and, for almonds, result in the russeting and cracking seen in the above fruit nuts. It is called “false” or “like” powdery mildew because it shows similar symptoms

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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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Cameron Zuber4 CommentsJuly 7, 2017Field Notes

Field Note: Impacts of Soil Variability on Tree Performance

The Almond Doctor Field Note is a new series of posts that will cover observations made from the field by staff research assistants of the University of California Cooperative Extension office of Merced County. While Field Note posts may reference completed or on-going research, its intent is share notable observations from the field, not to summarize research findings or describe current recommended farming practices.  Many people are aware that soil types play a significant role with tree vigor and productivity, as well as, affect management decisions relating to irrigation, pre-plant fumigation, fertigation practices, etc. However, many people do not consider how slight changes to soil composition and textures may affect trees and other cropping systems. To help illustrate this point, let us look at two problems recently faced by one Merced County grower with an almond orchard on sandy soil. The grower had a short-term and a long-term problem associated with the orchard. The short-term problem was the tree’s leaves were turning yellow. The long-term problem was variable growth and vigor in different sections of the orchard. Soil type, topography, and management practices were consistent throughout the orchard. What could have been the cause of the problems? The type and extent of yellowing was consistent throughout the orchard and within the tree canopy. The pale leaf color and lack of canopy growth within the orchard suggested that the trees were getting too much water. Typically, yellowing leaves only in the inner canopy indicate too little water, while consistent yellowing across the entire canopy indicate too much water (baring effects from diseases and pests). The conclusion of excessive watering was supported by heavily saturate soil samples days after the last irrigation event. While excessive water explained the yellowing leaves, it did not fully explain why different sections of the orchard were

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