You're welcome Bayarea-girl. The choice whether to retain a particularly "needy" plant is completely personal. I coddled Angel Face for years because of the color, scent and beauty it COULD provide, as long as I catered to its needs. I completely understand why someone would want to provide it the extra care. I have done that for many years to one of the most intractable roses ever introduced - Grey Pearl. Everything in Nature exists for a purpose. Rust (and black spot) are "geriatric diseases" as they primarily affect aging foliage. Mildew is a juvenile disease as it affects new growth first. Rust is actually used by Nature to trigger many species to stop their juvenile stage, cease flowering (ovulating) and trying to reproduce. R. Arkansana utilizes the increasing sunlight and warmth of spring to put the melting snow and winter/spring rains to use, triggering its "reproductive stage". It begins pushing new growth and flower buds along the previous year's growth in its effort to set seed and reproduce itself. Reproduction and perpetuation of the species are the "Prime Directive" in Nature. As long as those light, temperature and moisture levels continue, it (and many other once flowering types) continue pushing new growth, new flowers, in pursuit of that goal. As the year progresses, the sun rises higher in the sky. Heat intensifies and water begins to run short, making maintaining that growth and flowering push more of a strain on the plant. If it continued using its dwindling resources growing and flowering without preparing for the harsher winter conditions, it would either completely use them up prematurely and die, or enter the extremes of the winter weather where it is indigenous, unprepared for hard freezes and be killed by them. As the heat increases and water becomes increasingly scarce, it appears the plant's immune system is impaired and the species contracts rust to a rather heavy degree. The fungi impairs the plant's ability to feed itself, triggering it to begin "hardening off", altering the sap to conserve the moisture and nutrients it has absorbed and generated when conditions were better for it to push its growth. Hardening off conditions it to withstand greatly reduced light levels and much greater cold. Nature uses rust (and some other triggers) to "tell" Arkansana to stop expanding, stop reproducing, ripen its seeds and prepare to shut down for winter. You will see the same mechanisms at work with many weeds and other desirable ornamentals. Petty Spurge, a common "weed" member of the Euphorbia family, as well as many Oxalis follow the same cycle of growing until triggered to rust badly and shut down until better conditions arrive. It is entirely possible the contraction of rust by other types might be used similarly and be caused by similar triggers. I attempted to grow R. Arkansana in a large pot here in my garden. It suckers vigorously. I didn't want a yard full of the plant, nor did I want to have to irrigate a large stand of one type. I knew Arkansana's mature foliage rusts in fall, but I didn't expect the brand new foliage to rust immediately after unfurling, particularly in spring when nothing else was rusting. I theorized that it contracts the disease "in the wild" due to decreasing water, so I increased the water to that pot. The old, rusty foliage fell and was replaced by new, healthy foliage all over the plant. As long as I continued providing heavier water to it, the plant grew and flowered without contracting rust. Long before anything else in the garden showed any signs of rust, I cut back the water to my Arkansana. It began rusting almost immediately. Increasing the water again resulted in new, healthy foliage pushing all over the plant. As soon as I cut back the water again, even the new foliage developed rust. Arkansana has gone on to someone else's garden where it can enjoy greater water, more room and conditions closer to its natural habitat. I've grown a number of the Canadian cold hardy Arkansana hybrids. All but one performed the same way. As long as I provided the extra water and never permitted them to experience water stress, they grew and flowered well and remained healthy. As soon as they began stressing for water, all but Morden Blush rusted badly, very quickly. Morden Blush remained completely healthy in this climate. I really loved the whimsical veining and stippling in Morden Ruby's flowers, but I could not keep the foliage rust free unless I chemically treated it, something I refuse to do for a variety of personal reasons. So, that one is no longer in my garden. Eliminating water stress in this climate and my soil is virtually impossible. Varieties which can't endure that stress without quickly contracting rust simply aren't suitable for the variables I garden under. One of my favorite miniatures to use for breeding is Cal Poly. It is extremely fertile, thornless, accepts a wide variety of pollen, generates many very viable seeds and produces many thornless offspring. I grow them potted to make protecting their hips from squirrels and other rodents easier and to make access to their flowers for pollination more convenient. I quickly learned not to allow their pots to dry out too far or they rusted quickly. Grown in the ground, they've never rusted for me anywhere I've grown them. When I have rust (or other disease issues) on seedling roses I raise, I experiment with water levels in hopes of discovering whether that might make a difference in their health. Most often, it does. Of course, each variety, each seedling, varies quite a bit in its natural resistance to disease. Particular garden conditions as well as climate differences play enormous parts in the probability a variety may contract a disease. One of the easiest to control in your efforts to diagnose the cause of the infection is how much water, when and how the plant receives it. I would bet starting with that would help figure out whether the plant is suitable for where you are, the conditions you can't change and your preferences whether to chemically treat the infection or not. It has streamlined that determination for me greatly. Kim

Hmm, I thought powdery mildew was most rampant during drought - it certainly is on my verbena (of which I have far too much). Do you have downy mildew? That's common in cold wet areas, and we've certainly been cold and wet in NE this year. The site below (assuming GW will allow the link!) also suggests a weak vinegar rinse; I haven't tried it myself. I've also seen milk proposed as a good anti-fungal, and haven't tried that yet. If or when my peonies start showing signs of foliage problems, I think I'll try that this year. Here is a link that might be useful: mildew remedies

Thanks, Peter and Ig. The PM is already spreading to the acorn and butternut. I soaker hose long-watered yesterday and I pulled the gray, dead PM leaves off and put them into the trash bin. Someone I met suggested fish emulsion feed. Of course, I cannot now locate that small green bottle of stinky liquid. The soil drains well. Weedy area and some Heritage raspberries or maybe they are wild blackberries are sprouting up here and there. It's a constant challenge. I'm tempted to experiment on the two front zucchini plants: immunox on one and "copper spray" on another. (What sort of copper spray? Any drawbacks?). The butternut squash up hill at my neighbor's isn't particularly full, but doesn't have any noticeable PW either. It rained last night and this morning, so that should help. With no rain or moisture, how could any Epsoma or 10-10-10 break down to get to the plants? Question: if overhead watering contributes to Powdery Mildew, PM, then what about rainfall? Is rainfall any different than overhead watering (assuming minimal back spash of soil onto leaves)?

It definitely makes sense. Especially in cases like Bart and Mad Gallica describe. In my yard, I seem to only have issues with powdery mildew when it becomes more humid (here - that means rainy), but when it's still warm during the day and cooler at night. That usually equates to early fall. I don't seem to have issues with it during the dry heat of summer. The powdery mildew I just found on my roses that weren't mulched was the worse I can remember. And it really wasn't that bad. It was probably the worst on Iceberg of all roses! Bizarre! That one never gets mildew in my yard. I usually keep my roses very well spaced and mulched, with drip irrigation. I think that has really helped. I don't spray (usually). I have only really purposefully gardened in Northern California though, and our conditions are so different from most. I'm inland with a lot of dry heat ... and over the last few years with such severe drought conditions and weird climate changes. Although, since I found these forums I was thinking about squeezing everything together in order to fit more roses in! On second thought, I'm going to pull back and stick to my usual spacing after all. More roses will not be better if they're covered in mildew. More disease maintenance and pest control takes all the fun out of it! Thanks for explaining Roseseek. Nature using mildew and rust to help the plant defoliate in order to survive colder or hotter/dryer climates makes total sense. Your explanation for how mulch helps ward away mildew makes sense too... and fits with your explanation of what causes mildew. It's wonderful and invaluable to have such knowledgeable professionals like you on these forums. Thank you so much for making yourself available and sharing your wisdom.