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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 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. click on image for more information
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. click on image for further information
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.
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. see also "The Plant Clinic Year"
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May 14, 2009
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Oregon State University Plant Clinic 
