Disease Archives - West Coast Nut



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. P. syringae pv. syringae is an epiphytic bacterium which resides on plant surfaces. It’s safe to assume it’s in many orchards in California, however it will not invade the plant until conditions are conducive to infection: wet weather accompanied by freezing temperatures which can damage plant tissue. Even the mild...

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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, a University of California plant pathology PhD student who has studied wood decay fungi in almonds and prunes. Hull Rot Hull rot is a hull infection caused by one of several pathogens. Affected nuts don’t shake off at harvest and can become navel orangeworm (NOW) feeding sites if they are...

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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 problem in almond orchards, reducing yields and eventually causing tree decline and death. Yaghmour said the symptoms of ALS might not even be noticeable for several years after infection. Symptoms of this disease can be spotted in early June. Later in the growing season and close to harvest time, symptoms...

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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 these rootstocks in field trials.” Disease-resistant Rootstocks Disease-resistant rootstocks for commercial walnuts are a huge deal for growers, said Cliff Beumel, a long time walnut grower and nurseryman and President of the fruit, nut and olive tree nursery Agromillora located north of Sacramento near Gridley. “All growers eventually bump up...

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Managing Hull Rot in Almonds

Prevention of a fungal disease that can affect almond yields for many growing seasons starts with a correct diagnosis and understanding of disease biology. Hull Rot Almond hulls are susceptible to hull rot fungi from the beginning of hull split until the hulls are dry. This period can last from 10 days to two months depending on the irrigation and fertilization management of the orchard. There are no control measures once hull rot infections are visible. University of California (UC) Riverside plant pathologist Jim Adaskaveg identified the ‘deep V’ stage of hull split as the stage when almonds are most vulnerable to hull rot infections. Dr. Mohammad Yaghmour, University of California Cooperative Extension (UCCE) farm advisor for almonds in Kern County is conducting research to determine control measures for hull rot. He was one of the seminar speakers at Almond Day in June and outlined best management practices and treatment...

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