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Maple (Acer spp.) - Verticillium Wilt
Verticillium Wilt in the Pacific Northwest
Cause Verticillium dahliae has been recovered from branch or crown tissue of new 'Bluetta' blueberry plantings from Washington and Oregon but considered rare. Plants were 2-4 years old and found on the cultivars Aurora, Blue Ribbon, and Cargo. Plants had been grown where previous crops were potatoes and peppermint, both of which are hosts. The disease was worse on soils where the pH was above 5.5, which is higher than optimum for blueberry.
This is a soilborne fungus that may remain viable in soil for years. The fungus forms microsclerotia within infected tissues. Once in the soil they germinate and infect roots. The fungus grows into the xylem where it colonizes the plant through mycelial growth and conidial production. Fluid movement in the xylem passively transports the conidia. Once in the xylem, this fungus partially blocks water movement and produces toxins that result in wilt symptoms. Plant-parasitic nematodes also can increase disease incidence and severity.
Symptoms Plants had poor vigor, localized cankers due to opportunistic fungi, reddening or chlorosis of leaves, and numerous dead buds and twigs. Symptoms resemble a dieback. There was no internal discoloration of the xylem as is typical in some other hosts.
Sampling A preplant soil test for propagules of this fungus will aid in site selection. The presence of any microsclerotia in the soil should be interpreted as a potential disease risk.
Cultural control At this point there is no research-based information from blueberry so management tactics are borrowed from other crop systems where this disease is a problem. In all cases curative measures do not exist.
- Do not plant in soils where Verticillium-susceptible crops (such as potatoes and peppermint) have been grown previously.
- Control weeds.
- Avoid measures that promote succulent growth. Research on control of Verticillium wilt in other crops indicates that nitrogenous fertilizers should be used at minimum rates-sufficient only to provide normal growth.
- Crop rotation is of only limited benefit to reduce populations due to a wide host range and long survival in soil.
- Incorporation of green manures, cover crops, or other organic amendments into field soils prior to planting can be effective at reducing the impact of Verticillium wilt in some crops.
- Remove and destroy symptomatic or dead branches preferably before leaves fall and thus before new inoculum gets incorporated into the ground.
Reference Serdani, M., Wiseman, M.S., Inderbitzin, P., and Putnam, M.L. First Report of Verticillium dahliae causing dieback of highbush blueberry (Vaccinium corymbosum) in Oregon and Washington. Plant Disease, https://doi.org/10.1094/PDIS-02-17-0229-PDN