Phytophthora is ubiquitous. Almost any plant can suffer from this fungus, if the conditions are right. And THAT is the key (or part of it). Phytophthora can be present in the soil but unless conditions are right, most plants will be unaffected. Those conditions are poorly drained soil and/or excess rain for long periods of time, high water table, low spots in the topography, etc.

Yes, petunias can be one of the more susceptible plants. IF you take a good, honest look at the site conditions and feel that it is a healthy one for growing most plants (in terms of excess soil moisture), then all of the above plants should be fine. But put them in a location that remains soggy, then you can expect root rot (and other diseases) galore.

By the way, annual Vinca (Catharanthus roseus) is another very susceptible plant species.

Remember the triangle of disease, all three sides must be present for the disease to effect your plants. First side is the susceptible plant, next is the pathogen must be present, and the third is the condition must favor the growth of the disease. You cannot do anything about the fungus being present, it is everywhere. You CAN select a resistant plant, or you CAN change the growing conditions that are favoring the disease. When you have a disease problem in the garden I find using this thinking solves most problems. Al

Thanks. The growing conditions, so far as I know, are ideal. Full sun most of the day, well-drained soil that my husband rototills before we plant each spring, and this year, we didn't have long, prolonged periods of wet weather, though we did have some weird weather in early April. Hot weather in the 90's for a couple of days, followed by very cold weather and 5 inches of snow. But it's been pretty normal since late April.

the first year I planted things (2002) the ground had never had anything growing in it except grass. My husband rototilled an area next to our walkway out front and put in compost and some peat moss. I planted Proven Winners wave-like petunias, marigolds, zinnias, and red salvia. The petunias thrived and so did the marigolds, but the zinnias and salvia got eaten by bugs. 2002 was a good summer: warm, in the 80's and low 90's, with the right amount of rain.

But 2003 and 2004 were cold and wet summers, esp. 2003. Most of my annuals got the wilt disease, except allysum and the marigolds. The salvia didn't get it, but they still got eaten by bugs.

The summers since then have been pretty good, but I have not been able to grow petunias since, except on one small, narrow side of the walkway garden. I have 4 oblong concrete stepping stones leading from the walkway, over the garden, and onto the lawn. On the left side, the garden is narrow, and for some reason, the wilt disease doesn't affect the petnunias, 2 of them, that I plant there every year. Just on the other side of the stones, where the garden is much longer. There they get sick and die. The only thing I can think of is, that when it rains, lime leaches from the stepping stones into the soil, and kills any fungi that is in the soil, preventing the petunias from getting sick.

I have them planted on the left side of the garden this year. So far they are fine. However, this year, some of my plants have been affected by a leaf mold of some kind, that turns the leaf edges brown or puts brown blotches on the leaves. Sigh. However, I have sprayed with Physan20 and it has helped a lot. I have never had leaf spot on annuals before.