| Apple -- Union Necrosis and Decline | ||
| Cause: The causal agent of apple union necrosis is Tomato ringspot virus. The virus is spread by dagger nematodes, Xiphenema americanum (sensu lato). This pathogen occurs in many areas of Eastern North America, and has been reported occasionally in the PNW and California. | ||
| Symptoms: Signs of infection do not appear until the infected tree approaches fruit bearing age. At that time, the tree exhibits an unthrifty growth habit associated with an abnormally high fruit set. Symptoms may also include reddish coloration of the leaves and bark. In severe cases, a dark necrotic line will appear at the graft union flanked by spongy orange tissue. | ||
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| Cultural control: Primary control is by planting virus-tested (and found to be free of all known viruses) trees and in sites that have no history of the disease. | ||
| Chemical control: Disease development can be delayed and perhaps controlled by suppressing nematodes by fumigation if planting in a contaminated site. | ||
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References: Stouffer, R. F. and Uyemoto, J. K. 1976. Association of tomato ringspot virus with apple necrosis virus and decline. Acta Horticulturae 67:203-208. |
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| Content edited by: Ken Eastwell on January 1, 2009 | ||
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