See:
Azalea (Rhododendron spp.) - Botrytis Petal Blight
Cause Botrytis cinerea, a fungus. Growers observe that "purple" cultivars are more susceptible than others.
Symptoms A brown, water-soaked lesion in the middle of the shoot early in spring. The lesion is associated with a leaf node or stipule and may produce a mass of gray spores on its surface. Infected shoots bend over at the lesion and may remain crooked or die back.
Chemical control Apply once in spring when symptoms are first noticed.
- Astun at 10 to 17 fl oz/100 gal water. Group 7 fungicide. 12-hr reentry.
- Broadform at 4 to 8 fl oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
- Chipco 26019 FLO at 1 to 2.5 quarts/100 gal water. Group 2 fungicide. 12-hr reentry.
- Pageant at 12 to 18 oz/100 gal water. Do not use with organosilicone-based adjuvants. Group 7 + 11 fungicide. 12-hr reentry.
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 fungicide. 12-hr reentry.
- Terraguard SC at 4 to 8 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
Biological control
- Prestop (Gliocladium catenulatum strain J1446) at 0.33 oz/5 gal water. Do not use with other products in the tank. 4-hr reentry. O