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October Highlights

Things to watch for during October

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

Fungal disorders

Bull's eye rot in apple is aggravated by the onset of Fall rains, a time when the fungal spores of this desease will spread from limb cankers to maturing fruit and to young limbs and twigs.

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apple bull's eye rot

Box blight is a relatively recent fungal disease for Oregon but is expected to be increasingly prevalent. The disease is common on the east coast as well as in Europe and New Zealand. Symptoms include spots on leaves, and streaks or cankers on stems followed by defoliation. Nurseries should be on the look out when the Fall rains begin. The disease is favored by warm wet weather.

Box blight
box blight

Mechanical injury to potato tubers during harvest make them susceptible to disease during storage. Fusarium dry rot of potato is caused by species of Fusarium that occur in soil and debris. These fungal pathogens enter through wounds and the disease develops in storage. Soft rot bacteria often invade secondarily once a tuber has dry rot.

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potato fusarium dry rot

Viral disorders

Black raspberry decline, strongly prevalent in Oregon in the past 10 years, is an important virus disease of black raspberries caused by a North American strain of the Black raspberry necrosis virus that was characterized just two years ago. This disease is transmitted by the large raspberry aphid, and is often found together with one or more other viruses. Symptoms include leaf yellowing, mottling and puckering, fruiting cane dieback, and loss in yield. More information on the continuing work on this disease can be found here.

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black raspberry necrosis virus
black raspberry

Bacterial disorders

Common scab on potato is caused by the soil dwelling bacterium Streptomyces scabies. Young, developing tubers are infected through pore-like structures (lenticels) found on the outer surface, and occasionally through wounds. Reddish-brown spots develop on the surface of tubers which expand as the tubers grow and these become corky and necrotic. Potato varieties vary in susceptibility to this disorder.

common scab of potato

Abiotic disorders

Throughout the year we receive samples of plants with symptoms that cannot be attributed to plant pathogens. These plants are suffering from abiotic disorders which are of many different types. We focus this month on plants showing poor growth that can be associated with stress due to a lack, or an excess, of nutrients required for normal growth. As James Altland writes in his article on Plant Nutrition Diagnosis, an accurate diagnosis is achieved by soil testing and plant tissue analysis. Both field crops and nursery container crops are discussed in this article.


This is the time of year when the giant house spider (Eratigena atrica) tends to be more visible in your house as the males go in search of mates. They generally prefer secluded locations behind furniture but being more active at night you may see them running across the floor during the evening. Like the hobo spider (Eratigena agrestis), the house spider was introduced into North America from Europe. The fear associated with the hobo spider related to its so called venomous bite, may be unfounded. Nevertheless many people are not fond of sharing their home with these long-legged sprinters that are hard to tell apart, and so the Oregon Department of Agriculture has some recommendations.

see also "The Plant Clinic Year"