Pests & Diseases

Valley oak tree atop a hill of brown grass.
Event

Webinar: Mediterranean Oak Borer & Other Pest of California Oaks

Apr 10 2025

The Mediterranean Oak Borer (MOB) is an invasive ambrosia beetle that infests several species of white oaks in California: valley oak, blue oak, and Oregon oak. The beetle is spreading rapidly in Napa, Lake, Sonoma, and Sacramento Counties and has been detected in neighboring El Dorado, Yolo, and Mendocino…
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Armillaria
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Armillaria

 Armillaria root rot, also known as Oak root fungus, is a disease of many different plants.  There is no known effective cure.  Root rot fungus disease of trees and woody plants. Affects palms, succulents, ferns and other herbaceous plants like begonia, daffodil, dahlia, and geranium.  No…
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Damping Off
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Damping Off

Seedlings sometimes fail to sprout or die soon after. Seeds may rot before germinating, shoots may decay before they emerge, or stems of seedlings may be attacked near the soil line, causing young plants to collapse. These diseases are collectively called “damping off,” likely caused by a number of soil…
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downy mildew
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Downy Mildew

Downy mildews, including Peronospora and Plasmopara spp., are pathogenic water molds (oomycetes) that primarily damage foliage. Hosts include cane berries, roses, various herbaceous ornamentals, and many fruit, grain, and vegetable crops. CategoryFungiSigns/SymptomsDowny mildew causes pale green to…
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Brown, scorched-looking leaves are symptoms of fire blight in trees in the apple and pear family. Photo: Sebastian Stabinger
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Fire Blight

 Fire blight is a common and frequently destructive disease of pome fruit trees and related plants.  The disease can destroy limbs and even entire shrubs or trees. Caused by the bacterium Erwinia amylovora. Pear (Pyrus species) and quince (Cydonia) are extremely susceptible.  Apple, crabapple …
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fusarium wilt
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Fusarium Wilt

Fungus that only infects tomatoes. Like verticillium, causes leaf yellowing and discoloration of water-conducting tissues. Fungi spread in soil water, on equipment, transplants, or tubers. Once inside the root, the fungus grows until it reaches the water-conducting cells, inside which it spreads upward…
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blight
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Late Blight on Potatoes

Late blight of potato was responsible for the Irish potato famine of the late 1840s. Late blight is caused by the oomycete Phytophthora infestans. Oomycetes are fungus-like organisms also called water molds, but they are not true fungi. CategoryFungiSigns/SymptomsLesions appear as small dark green water…
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peach leaf curl
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Peach Leaf Curl

 Fungal disease that affects the blossoms, fruit, leaves, and shoots of peaches, ornamental flowering peaches, and nectarines. One of the most common disease problems for backyard gardeners growing these trees. When severe, the disease can reduce fruit production substantially. The loss of leaves and…
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powdery mildew
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Powdery Mildew

 Powdery mildew is a common disease on many types of plants and is prevalent in many areas of California. Infection occurs when fungus contacts a suitable host and environmental conditions are favorable. Infections spread as spores produced in these white patches move by wind and splashing rain to other…
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