Phlox 'David' and powdery mildew

17 years ago

Ok, I kept reading that Phlox "David" has exceptional resistance to powdery mildew.

Late last summer/ early fall I bought one from a reputable local nursery. I've bought several things from this nursery before, and always had good luck. The plant was a bit straggly because it had been potted up for a long time, and cut back after blooming. I put it in the ground and it continued to have a few blooms, and then it came down with powdery mildew on the bottom half of the plant. I did not think much of it because it was under stress, but its roots were healthy and I was looking forward to seeing it perform this year.

It came up beautifully in the spring, and it is large and lush and healthy--- but the powdery mildew is back. I have removed the worst-infected lower leaves and started spraying it with a milk solution that I read can be effective. If that does not work I will probably break down and get a fungicide, as this is in a front bed right off my porch and in plain view.

However, what happened to the superior mildew resistance of "David"? Is it overtouted for mildew resistance? Is it possible I got a different white cultivar and it was misnamed in the pot?

It gets nearly full sun in a south/southwest exposure, and is in amended soil with some Endless Summer hydrangeas which are thriving (despite getting too much sun). It does occasionally get some oversplash from the gutters in a heavy rain, and when that happens the soil probably takes awhile to drain, but otherwise it's in well-drained soil. We have had a spring with enough rain, and when we had one dry week I did water it, so it's not under stress (or shouldn't be).

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soitgoes
Original Author

17 years ago

Thanks for your input. However, I am well aware of the dangers of planting in a hole surrounded by clay. This plant is in a bed, and the entire bed was dug and amended with leaf soil, compost, and good purchased top soil.

There are spring bulbs in the bed, as well as the two hydrangeas I mentioned. The bed is of a good enough quality that I never got so much as a leaf wilt on the hydrangeas, even though they are in full sun, which is not their ideal amount of light. And the bulbs have not rotted, which they normally would in poorly drained soil

The bed is marooned, surrounded on all side by sidewalks, driveway, or porch, so it has some limitations but as I said, it is normally well-drained unless we get one of those storms where we get an inch of rain in 15 minutes. That may happen once a month or so, tops.

It might not like how close it is to the concrete foundation. However, I am frustrated because I thought the plant was resistant. While I realize "resistant" does not mean "immune", I did not expect it to have it's lower 10% of leaves fully covered with powdery mildew by May. It's not even summer yet, and I'm in zone 5. The spring has been a bit rainy, but my mom has a whole bunch of old-fashioned non-resistant phlox, and they normally don't get PM until July or so.

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Comments (6)

Kimmsr
17 years ago
While Powdery Mildew is supposed to be more common on plants that have limited air flow around them some plants that are very susceptible will get it even if they are out where air flows freely. Resistance to something does not mean a plant will not get the problem, but look closely at the soil this is growing in and make sure that soil is a good, healthy soil well endowed with organic matter that is evenly moist but well drained. I just saw another article about making a $50.00 hole to plant a $5.00 plant umplying that every hole a plant goes into needs to be really well amended while ignoring the surrounding soil and in clay soils that can be detrimental to the health of any plant planted like that. So while that may be true of a soil that is well drained soil needs to be gotten there first. Take a good look at the soil "David" is planted in and be sure it is what it should be to grow a good, healthy plant.
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rhizo_1 (North AL) zone 7
17 years ago
They don't declare a phlox 'resistant' because of an ability to avoid the disease, but on how MUCH of the plant is likely to be infected. Your estimate of 10% foliage infection seems pretty darned good for this very very susceptible plant. I think that you can improve the odds with some year round techniques.

Be sure that you take care of all of the management chores of PM prevention and you can probably improve your plant's appearance in upcoming seasons. You ought to try neem, which is highly recommended for the control of PM in phlox.
soitgoes
Original Author
17 years ago
I was hoping to get some feedback from other people who have "David" to see how it performs for them.

Rhizo, 10% infection would be pretty darned good if this were July or August, but here in PA May is not even powdery mildew season. Phlox normally does not get hit til near the end of summer, even the non-resistant varieties. My plant has severe enough infection to have total dieback on the bottom of the plant, and in the midsection of the plant the leaves are spotted. Only the very top is free, but we have 4 full months left to go. When I go online and read studies of powdery mildew, generally you don't see the studies make claims about resistance of plants or effectiveness of control products until late in the year; they are usually ALL fairly resistant/effective this early on in this climate.

I spoke to the woman at the nursery and she was visibly surprised that I had that problem with that plant. She suggested trying to move it, but it doesn't have any place else it could go where it would be happy.

When I pulled off the infected leaves at the bottom, it made the plant top-heavy which caused it to open up a bit as the stems all lean outward. That should help, but I am disappointed. My mother does not treat her phlox. She has some old unnamed garden phlox that is not meant to be resistant, her plants are huge and full and the earliest in the year they ever get a speck of mildew is mid-to-late summer. In a very bad year she might have dieback, but in many years they hardly get any and never once has she had it in the spring.
Donielle Stenson
4 years ago
ive had the same frustrating experience. I fact it is the most P. Mildew prone phlox in my garden.

Disappointed is an understatement
Donielle Stenson
4 years ago
last modified: 4 years ago
total die back before setting flower heads. The leaves look gross.. Neem is toxic to beneficial insects I'll yank it up if it doesn't improve. Going on 3 years. Other phlox are gorgeous. This one is a problem so