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Disease



Bacterial Canker and Blast in California Almond Trees


Bacterial blast and bacterial canker are caused by the bacterium Pseudomonas syringae pv. syringae (Pss). Both diseases are a tough problem to deal with in almond and stone fruit orchards. Bacterial diseases are more common in cold and humid regions causing significant damage to orchard trees. However, we can still see both diseases causing significant losses under certain conditions here in California. As detailed below, it doesn’t require existing wounds for infection (but they certainly can increase a tree’s vulnerability), it is exacerbated by but doesn’t need plant stress to infect, and it currently has no effective chemical control options....

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Hull Rot and Ganoderma Root Rot in Almonds


Hull Rot is an infection in almonds caused by one of several pathogens. The infection not only causes quality and yield problems with the current crop, but it can impact the following season’s production. Current Research Current research findings, water and nitrogen management recommendations and chemical control options were reviewed by Mohammad Yaghmour, Kern County University of California Cooperative Extension (UCCE) advisor at the Almond Conference. In addition to Yaghmour’s hull rot research, current information on the wood decaying fungi Ganoderma that affects almond tree health was provided by University of California (UC) Davis researcher David Rizzo and Bob Johnson,...

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Understanding Almond Disease Vectors and Recognizing Disease Symptoms


Understanding disease vectors and recognizing disease symptoms can allow for timely management decisions in almond production. Mohammad Yaghmour, University of California Cooperative Extension (UCCE) orchard systems advisor for Kern and Kings counties, explained differences and similarities among vector-transmitted bacterial and viral disease of almond trees and how the diseases are transmitted at the South Valley Nut and Citrus Conference. A typical disease triangle includes host, pathogen and environment, Yaghmour said, but vectors can also play a part in spread of disease. Almond Leaf Scorch The bacterial disease Almond Leaf Scorch (ALS) is vectored by insects and can become a chronic...

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Walnuts and Crown Gall: What It Is and How to Manage


Crown gall—the tumors or galls that can appear on the roots, trunk, and crown of a tree—is nothing if not unsightly, but these abnormal masses that appear on walnut trees stem from a more involved process. Agrobacterium tumefaciens While a nuisance to growers and a hindrance to trees, Agrobacterium tumefaciens— the bacterium responsible for crown gall—has actually made an impact on humankind and medical advancement due to its ability to transform a cell into what the bacterium needs it to be, making it a key player in genetic engineering. But to put it succinctly in regards to orchards, A. tumefaciens...

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The Latest on Disease Resistant Rootstocks


Significant progress is being made in the development of walnut rootstocks that possess resistance to the major yield limiting diseases and soil-borne pathogens. “We are now working on putative disease resistant walnut genotypes which are being propagating to test in large scale field trials to determine how they perform compared to the greenhouse evaluations, “ said Dan Kluepfel, United States Department of Agriculture (USDA)/Agricultural Research Service (ARS) research scientist and principal investigator of the walnut rootstock development program. “This is not just an academic pursuit. We have something in hand and in collaboration with nurseries are moving forward to place...

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