They have Powdery Mildew now? It is awfully early in zone 5 for that, at least around here. PM is more usual later in the summer when the weather is hot and humid, and then it is easily controlled by either a spray made of 1 teaspoon baking soda mixed in 1 quart of water, or a 50/50 mix of fat free milk and water, sprayed every 5 to 7 days until the problem is cleared up.

PM will certainly appear on Ninebark early in the season, as it is a VERY susceptible host. As a matter of fact, early infection is one of the characteristics for this plant. PM infections tend to be species specific....meaning that the spores affecting your Ninebark cannot infect other plants.

Since you have so many of these disease prone plants, have you been attending to the important 'housekeeping' chores that can help mitigate the damage? Fall and winter clean up can be a key step in lessening the PM pressure.

Consider select pruning to allow for increased sunlight penetration and air circulation, both of which will really slow down this disease.

Sprays of regular water can also help, early on in the season. Washing the foliage can prevent the spores from infecting the internal cells. So, too, can applications of Neem, something that I have had a great deal of success with in the treatment of PM on susceptible plants. Neem can not only prevent infection, but acts as an eradicator, as well. Light weight horticultural oils can be of great help, as well.

Without the application of housekeeping tasks, preventative spraying, improved management of sun and air, your fungicidal applications may fall short of success. If you work with ALL of the tools, you can probably control this disease without the need for commercial, chemical fungicides.

I only planted these 1 year ago and they showed signs of the mildew within a couple weeks of planting them.

Since then I have been plucking, spraying, pruning and watering properly. I even cleaned up the foilage in the fall.

These plants are in a well drained southwest location, even out in the open so its a joke that all 7 have the mildew.

I'm thinking about pulling out 4 of them. The nursery has already agreed to take them all back, its just a ton of work to take these 3 - 4ft out.

My concern is that if its this bad this early, with maintinance and with conditions that aren't condusive to the PM that I'll be fighting with them forever. What happens when the get 6 ft tall?

My other MAJOR concern is that the PM will spread to other plants. I have maple, spirea, pear, viburnum, forsythia and lilac within close proximity. I know the host my be specific but I can't get a straight as to the PM spreading or not.

I guess I need to find a replacement that is more pest and disease resistant. Any suggestions for 7ft x 7ft plant that will get southwest exposure, likes a well drained soil that will get dry, so they need to be drought tolerant once established. Of course I need good shape, good branching and an ornamental feature since they are in a high visible area. Lastly needs to be PM resistant, lol.

The FUNGUS species is host specific. There are hundreds (maybe more) unique species of powdery mildew species. They are very specific as to the plants they are able to infest. I don't know the exact species that may attack the ninebark, but it is not likely to bother anything else but other ninebark. 'Maybe' the pear, which is also in the Rosaceae family, but I doubt it. If (when) your lilac ends up with powdery mildew, it will not be from the ninebark.

It sounds like you've done all you can do to provide a good environment for your plants. The only remaining factor is the fact that those plants are highly susceptible to this particular disease.

Well I guess that is the main thing, I have too many of one plant that are extremely suspectible to PM.

I'll probably take the worst (least vigorous) plants out and return them.

Its been driving me up a wall because I have a arborist that says he can't say for sure the PM won't effect the other plants, then I have a nursery telling me that the Pear is the least likely to get it.

Do you have any suggestions for a replacment for the Diablo that is PM resistant?

- Zone 4/5
- Full Sun (partial sun in 10 yrs)
- Well Drained Soil
- Has ornamental features
- Drought tolerant once established (plants that don't require consistant moist soil)

Don't be frustrated! Do a tiny bit of research on the EDU sites about powdery mildew. You'll find plenty of good IPM tactics, as well as the information that PM is NOT transferable from plant family to family. That's common knowledge and something that your arborist and the nursery professionals should understand.

I mentioned the pear only because it is in the same family as your beleaguered ninebarks. SOMETIMES, the disease can make the jump to closely related plants. I'd wager that the pears are going to be fine, too, however.

If you do read up on this disease, be sure to visit more than one site. The EDU sites are probably best for this type of information, but some may be a bit lean on IPM practices.

Here is a link that might be useful: Here's one fact sheet for you