Things to watch for during June
From our experience of samples we have received during June in previous years in the OSU Plant Clinic, this page will highlight some problems that may occur this month. Again this year we are in advance by a few weeks in terms of disease occurrence because of recent warm weather, however despite recent very hot conditions the remainder of June is forecast to be cool and damp - perfect conditions for plant disease.
Cindy Ocamb reported recently that black leg and Phoma leaf spot in Brassicaceae fields in the Willamette Valley. Fall planted seed fields and wild populations of oilseed canola, field turnip, forage Brassica, Brassica cover crops, cruciferous vegetables (cabbage, collards, kale, and mizuna), volunteer giant mustard, volunteer turnip, volunteer black mustard, volunteer or wild radish, and wild mustard are all involved. The fungus Phoma lingam has been found in Benton, Linn, Marion, Polk, and Yamhill counties. Leaf spots and stem cankers are the main symptoms. This continues to spread according to a recent communication.
Jay Pscheidt reports heavy and early symptoms of powdery mildew on a wide variety of fruit crops from tree fruit (apples) to small fruit (blackberry, raspberry and strawberry) to grapes, as well as ornamentals.
Look for recovery in blueberry already affected by Blueberry Shock Ilarvirus (BSIV). Bushes should produce new leaves and appear relatively normal as the season progresses, although they will not produce much fruit. If recovery does not happen then, although uncommon, Blueberry Scorch Virus (BBScV) may be present, with tip dieback and flower blight starting in a few branches and spreading to the entire bush over 1 - 3 years. Plant material should be tested to confirm the virus.
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We continue to see symptoms of Fall infection of Barley Yellow Dwarf Virus (BYDV) on grasses for seed as well as other cultivated and wild grasses with yellowing leaf tips (reddish in oats). BYDV is transmitted by several species of aphid.
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Fireblight in apple and pear is caused by the bacterium Erwinia amylovora dark, water-soaked lesions can occur on spurs, blossoms, and twigs and then they turn brown to black and rapidly wilt and die. Infected blossoms can be distorted. Branch and trunk cankers appear dark and watersoaked. Young trees may be severely damaged.
Remember that any damage caused by unusually cold temperatures last winter can result in the establishment of secondary pathogens (winter injury).
see also "The Plant Clinic Year"