Below is my submission to the 2009 Proceedings of the Almond Board of California. This information will be presented in a poster at the 2009 Annual Conference of the Almond Board of California. It is important to note that this summary will be used to help re-direct current almond production research to provide future management practices for the problems found.
Survey of diseases associated with decline of almond orchards in Merced County
Objectives: Merced County has been a major producer of almonds for over 60 years, with an estimated 88,000 bearing and 3,500 non-bearing acres. Orchards have been established on a large diversity of soil types, irrigated with varying water quality, and managed with different orchard practices. Many blocks have experienced tree loss from Phyophthora crown rot, Armillaria Root Rot, Almond Leaf Scorch, Silver Leaf, Nematodes (Root-knot, Ring, and Lesion), Crown Gall, and wood decay pathogens. These diseases, in severely affected orchard blocks, have caused the loss of many trees, shortening the production life of those orchards. This survey, which will be conducted through farm visits, will help determine abiotic and biotic causes of orchard problems, while aiding in the extension efforts between the newly hired farm advisor and county growers.
Summary: The survey was conducted during farm visits. Visits made for this projects were requested by the orchard operator in order to help with an identified problem. A survey addressing management practices was developed and used to evaluate each orchard. Diagnoses of disease and tree problems were confirmed through tissue/soil sampling, isolation of pathogens, and discussions with advisors and consultants. In some locations where nematode problems were suspected, soil samples from 3-5 locations in the orchard were submitted to UC labs for nematode population counts.
A total of 52 orchard visits were made during the 2009 growing season and the diagnosis associated with the problems can be seen in table 1. 16 (30.7%) and 36 (69.3%) orchards were diagnosed with abiotic and biotic problems, respectively. Abiotic problems included herbicide drift injury, nutrient uptake toxicity, salt burn, and water stress. Of the biotic diseases, 9 orchards (17.3%) were identified to have root problems, with four orchards being diagnosed with Armillaria mellea (Oak Root Fungus). 17 orchards (32.7%) displayed symptoms of scaffold diseases, which include lower limb dieback and fungal cankers associated with pruning wounds (Eutypa and Botryosphaeria). The high occurrence of scaffold diseases suggests that a review of canopy management practices should be made. Samples collected from this survey have contributed to the first isolation and identification of the fungal disease Eutypa lata in almond. Pathogenicity tests are currently being conducted.
Nematode sampling was performed in 12 orchards, and the population levels detected can be seen in table 2. All 12 orchards were located in sand to loamy sand soils. High counts of Lesion and Ring nematode were found in 7 (58.3%) and 5 (41.6%) orchards, respectively. Orchards infested with lesion nematode often had counts above 1000 nematodes/liter (data not shown). It is important to note that genetic resistance to lesion nematode has not been identified in almond rootstocks, and should be addressed in future development.
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