Powdery mildew on Camilla - treatment and control
Yesterday I discovered powdery mildew ( see photo) on my Camilla bush next to my house. I have been out of town for 10 days so I don't know exactly when it started and I don't think it was present before I left. I generously sprayed neem oil on the under and tops sides of the leaves yesterday as soon as I discovered the mildew. I planted this Camilla 4 years ago and this past Feb/ March it had the best flowering season ever and a large growth spurt. The bush is otherwise very healthy looking and new flower buds are forming. I have 3 other camillas but they are in a different planter area about 25 yards away- and I have not seen powdery mildew on them. 1). For the other camillas should I spray them now with neem oil to prevent any mildew spores from forming or are they too far away for that to be an issue? 2). For the infected Camilla, is neem oil the best fungicide to treat ( kill) the powdery mildew and if so, how often should I re-spray ( the bottle said every 7 days but is that until it appears gone or do I treat more often now)? 3). I have read that powdery mildew is not usually fatal and that it is species specific ( i.e. Won't spread to the azalea or rose bush next to it) -- please validate this for me 4). I did remove a few heavily infected leaves and couple small branches down low - and I destroyed those ( burned them) - did I need to do this ? Should I remove more leaves? I also removed and destroyed all leaves that had fallen on the ground. 5). Anything else I should do to save this beautiful bush ? I live in St Mary county - a mile south of St Mary college and historic St Mary City.
Powdery mildew may not be an issue next year. Susceptibility can vary by cultivar. We do not recommend spraying the shrubs not affected. You will have to monitor as this may eventually change.
You can use a registered fungicide, neem oil, or horticultural oil products labeled for powdery mildew. Follow directions on the label. Fungicide treatments can help to protect new or un-infected foliage they are not curatives. If you spray, you can do this as soon as you see signs of the mildew.
The mildew will not spread to other plant species. However, certain plant species are susceptible to powdery mildew and it may be a different genus of mildew.
Remove fallen leaves to prevent any overwintering spores. You do not have to remove the foliage on the plant. Burning is not recommended.
See our website for more information on powdery mildew http://extension.umd.edu/hgic/powdery-mildew-trees-and-shrubs