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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

Look symtptoms of Blueberry Mummyberry. Spores produced from these are spread by wind to infect leaves and flowers as the buds open. You may now see the primary symptoms of this disease, browning and withering of flowers. Blighted flowers produce a second type of spore that spreads to healthy flowers.

Brown rot blossom blight of stone fruit (fruiting types as well as flowering ornamentals) is coming on strong due to the warm March rains (if trees were in bloom). 

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.

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Compare box blight with Volutella leaf and stem blight.

Stripe rust in wheat has been found early in the season in the last few years, as early as January,  by growers in the Willamette Valley, indicating that the fungus causing this disease has overwintered in the field.

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stripe rust wheat

The OSU Plant Clinic has been receiving samples of downy mildew in greenhouse roses, and powdery mildew in some greenhouse plants (Sedum, Veronica).

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rose downy mildew

sedum powdery mildew

veronica powdery mildew

Look for light leaf spot and black leg that remain prevalent in brassica fields, especially in those in which it was present last year and no fall fungicide application was made. We highlighted these fungal problems last month.

Species of Phytophthora can account for nearly half of the fungal diseases we receive at this time of year on samples of woody ornamentals. 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 is abundant, 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

As grapevines start to come into leaf, scout for trunk diseases documented in these two presentations.

Viral disorders

Look for Blueberry Shock Ilarvirus (BSIV) which 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 and this year there is less Pseudomonas around.

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blueberry shock ilarvirus

blueberry shock ilarviurs

blueberry shock ilarviurs

Bacterial disorders

Bacterial blight on lilac might be a problem as that has taken off due to the recent March rains.

lilac bacterail blight

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

Abiotic disorders
Sudden low temperatures during spring can injure new growth on plants, or young plants that have not fully hardened off. We have had a mild start to the year but frost can still happen.

see also "The Plant Clinic Year"