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April Highlights

Things to watch for during April

From our experience of samples we have received during April in previous years in the OSU Plant Clinic, this page will highlight some problems that may occur this month.

Fungal disorders

Fruiting bodies (apothecia) of Blueberry Mummyberry may start coming out about at the beginning of April from overwintering mummies at or near the soil surface. Spores produced from these are spread by wind to infect leaves and flowers as the buds open. The primary symptoms of this disease, browing and withering of flowers, could be expected to show up later in the month as the plants begin to flower. Blighted flowers produce a second type of spore that spreads to healthy flowers.

Box blight caused by the fungus Cylindrocladium pseudonaviculatum is a relatively new disease to Oregon. We encourage looking out for dark spots on leaves, dark streaks on stems and defoliation in boxwood plants. Already this year we've had some samples with this fungus.  

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Compare box blight with Volutella leaf and stem blight.

Stripe rust in wheat is again being found early in the season by growers in the Willamette Valley, indicating that the fungus causing this disease has overwintered in the field. Although the cold winter of 2013-2014 has enabled much less of the fungus to survive.

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stripe rust wheat

Watch for the fungus that causes downy mildew in onion.  Look out for symptoms in April beginning with pale spots on leaves which then develop into a gray/violet furry mold.

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onion downy mildew

Nearly half of the fungal diseases we receive at this time of year on samples of woody ornamentals are due to species of Phytophthora. Symptoms may occur both above and below ground including root rot, branch dieback, stem canker and are associated with poor drainage. Jay Pscheidt discusses symptoms, detection and management of Phytophthora diseases in his PNW Plant Disease Management Handbook article.

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ornamental cherry-Phytophthora
Ornamental cherry

Orange rust in black raspberries, seen as orange pustules on the underside of leaves is caused by a different fungus (Arthuriomyces peckianus) to the one in blackberries (Gymnoconia nitens). Symptoms are similar for both.

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black raspberry orange rust
black raspberry

Abiotic disorders

Sudden low temperatures during spring can injure new growth on plants, or young plants that have not fully hardened off. An excellent discussion of Winter Injury in Landscape Plants can be found in the PNW Plant Disease Management Handbook.

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perennial ryegrass - cold injury
Perennial ryegrass

Iris - cold injury

bear's breeches - cold injury
Bear's breeches

Pieris - cold injury


Viral disorders

Later in the month Blueberry Shock Ilarvirus (BSIV) may become apparent if flowers and young shoots suddenly die when the flowers are about to open. Entire bushes or parts of branches may show symptoms as a shock reaction to this viral infection transmitted in pollen by bees and other pollinators. Warmer weather may bring on symptoms of blueberry shock including dead buds on green stems. The bacterial problem Pseudomonas syringae can look similar but for those usually we see dead buds on dead shoot tips.

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blueberry shock ilarviurs

blueberry shock ilarviurs

Bacterial disorders

Bacterial soft rot, caused by Erwinia carotovora ssp. carotovora, and Pectobacterium carotovorum can affect vegetables (both tops and roots), bulb and rhizome crops. The bacteria survive in soil and plant debris and enter plant tissue through wounds caused by insects, other disease organisms, or mechanical equipment. Favored by high humidity, high moisture, and mild temperatures, the bacteria spread in the tissue causing a water soaked appearance that develops into a mushy breakdown and soft rot. Bacteria are spread in the crop by insects, rain, infected plant tissue, and tools.

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turnip soft rot

calla lily rhizome soft rot
calla lily



see also "The Plant Clinic Year"