Cause Exobasidium vaccinii (formerly Exobasidium oxycocci), a fungus. The disease occurs occasionally in some Pacific Northwest beds. It has a 1-year life cycle-infections in spring do not develop symptoms until the next spring. Basidiospores produced on thickened lateral shoots infect nearby lateral buds on new shoot growth. Spores are forcibly discharged, and wind carries them around the bed. Yield on infected fruiting uprights is reduced by a third; that is, yield falls 5% in a bed with 15% infected uprights.
Symptoms The fungus normally attacks only the axillary buds, causing them to produce abnormal branches with thickened, hypertrophied, rose-colored leaves that resemble miniature roses-hence the name. The fungus occasionally attacks terminal buds and blossoms. Infected blossoms are deformed and usually enlarged. Affected berries are deformed.
- Improve drainage in low areas of the bed.
- Remove trees around the bed to decrease shade and improve air circulation.
- Avoid over-fertilization.
Chemical control Make two (2) to three (3) applications (at 10- to 14-day intervals) starting as soon as rose blooms begin to take on a whitish cast (indicating basidiospore formation).
- Badge X2 at 3.5 to 7 lb/A. Group M1 fungicide. 48-hr reentry. O
- Bordeaux 8-8-100 (also use a spreader-sticker). Moderately toxic to fish. Group M1 fungicide. O
- Champ WG at 4.2 lb/A. Extremely toxic to fish. Group M1 fungicide. 48-hr reentry.
- Cueva at 0.5 to 2 gal/100 gal water/A. Group M1 fungicide. 4-hr reentry. O
- Cuprofix Ultra 40 Disperss at 5 lb/A. Highly toxic to fish. Group M1 fungicide. 48-hr reentry.
- Kocide 3000 at 3.5 lb/A. Highly toxic to fish. Group M1 fungicide. 48-hr reentry.
- Mancozeb products such as Dithane, Manzate Pro-Stick, or Penncozeb 75 DF at 3 to 6 lb/A or 2.4 to 4.8 quarts/A. Do not apply within 30 days of harvest. Can apply through several types of irrigation systems; see manufacturer's directions. Moderately toxic to fish. Group M3 fungicides. 24-hr reentry.
- Nu-Cop 50 DF at 4.2 lb/A. Slightly toxic to fish. 48-hr reentry. Group M1 fungicide. O
Reference Bristow, P.R. and Windom, G.E. 1991. Evaluation of fungicides for rose bloom control in cranberry. Fungicide and Nematicide Tests 46:80.