Cause Various pathogenic fungi have been found in association with leaf spots and twig blights in Oregon. This includes Allantophomopsis lycopodina on the cultivars Erntesege, Erntekrone, and Koralle; Phomopsis columnaris on cv 'Koralle'; Phytophthora citricola and Coleophoma empetri on cv 'Red Pearl'; and Rhizoctonia sp. on cv 'Koralle'. Many of these fungi are favored by wet weather and survive on dead plant debris. Various weak or opportunistic pathogens are also associated with tissues injured by frost or on senescing tissue, including Pestalotiopsis and Volutella.
Symptoms Each of these fungi were found in plants with dark purple-black leaf spots, leaf blight, or twig dieback. Infection by Phomopsis columnaris eventually resulted in whole plant dieback of the cultivar Koralle. There were no distinctive characters that would allow a diagnosis to pathogen based only on symptoms alone. Laboratory confirmation is necessary to distinguish which pathogens may be present.
Cultural control No specific control tactics have been developed for these fungal problems. The following may help reduce disease pressure.
- Remove and destroy dead plant debris.
- Avoid practices that might keep plants wet for extended periods of time.
Chemical control
- Abound at 6 to 15.4 fl oz/A is registered and may be useful during wet weather. Do not apply with silicone-based surfactants. May be applied the day of harvest. Group 11 fungicide. 4-hr reentry.
- Miravis Prime at 13.4 fl oz/A. May be used day of harvest. Group 7 + 12 fungicide. 12-hr reentry.
- Proline 480 SC at 5.7 fl oz/A. Do not use within 7 days of harvest. Group 3 fungicide. 12-hr reentry.
- Propiconazole-based fungicides are registered and may be useful during wet weather. Do not use within 30 days of harvest. Group 3 fungicides.
- PropiMax EC at 6 fl oz/A. 12-hr reentry.
- Tilt at 6 fl oz/A. 24-hr reentry.
- Quadris at 6 to 15.5 fl oz/A. Do not apply with silicone-based surfactants. May be applied on the day of harvest. Group 11 fungicide. 4-hr reentry.
- Quadris Top at 12 to 14 fl oz/A. Do not use within 7 days of harvest or mix with insecticides due to bee toxicity. Group 3 + 11 fungicide. 12-hr reentry.
- Quash at 2.5 oz/A. Do not use within 7 days of harvest. Group 3 fungicide. 12-hr reentry.
- Switch 62.5 WG at 11 to 14 oz/A is registered and may be useful during wet weather. May be used up to and including the day of harvest. Group 9 + 12 fungicide. 12-hr reentry.
Reference Farr, D.F., Castlebury, L.A., Rossman, A.Y., and Putnam, M.L. 2002. A new species of Phomopsis causing twig dieback of Vaccinium vitis-idaea (lingonberry). Mycological Research 106:745-752.