Exactly, Warren. It does seem ironic to me that here, Foetida is completely clean in most situations. It doesn’t GET our black spot, but the “confused” foliage its offspring are burdened with are martyrs to it, where conditions are right. The only thing that ever made sense to me was conflicting genetic instructions.
You take any short season, deciduous species, with its 'wait to push out those leaves, use them up quickly and dump them" instructions, whether it’s due to drought, sufficient freezing or the fungal triggers provided to force the plant to harden off for winter. Mix with long season, ever green types with their instructions to gradually create foliage meant to last a whole season/year, before sufficient plant growth shadows them, when they are reabsorbed and shed, often with little fungal intervention required. What resulted were plants, selected for their “beauty”, novelty, “pretty face” instead of health and longevity outside of their initial selection climate and conditions, reacting to climatic, cultural conditions and situations which triggered their natural predispositions to defoliate. Their “instructions” told them to hurry and push the leaves, use them up quickly (short season) on plants which were “told” to hang on to their leaves because they would need them a long time (ever green). Very confused immune and operating systems.
Many species have evolved utilizing fungal attacks to help them survive. Nutkana and Arkansana develop rust later in their seasons, causing them to defoliate. Makes sense. Their climates usually don’t provide rainfall that late in their seasons to help them maintain their foliage and immune systems in healthy states. Dropping the foliage “early”, prevents them from continuing to attempt growing into weather conditions which would result in their becoming so water stressed, they would defoliate in an attempt to not die from it, which would probably sufficiently weaken them, preventing them from hardening off in order to withstand colder winter weather. Arkansana can be forced to rust, even on brand new foliage, simply by water stressing it. I’ve done it. Increasing the water permitted it to generate new, uninfected foliage. Withholding water stimulated that new foliage to rust and fall. Providing more water stimulated formation of new, uninfected foliage. Putting them in climates which don’t require the fungal attacks to defoliate them for survival, extends the time the plant is triggered to maintain foliage cover well past the useful life, into ‘senility’, when infection is a given without chemical intervention.
Rugosa and many close hybrids, are terrible in this climate. Rust and black spot infections are heavy, I believe for several reasons. The season is too long, triggering the plant to hold the foliage well into senility when it’s most susceptible. The weather conditions are conducive to infection at the time the foliage is sufficiently senile to become infected. Nothing in this climate triggers the plant to shed the senile foliage other than fungal infection. “Confuse” the genetic instructions further by adding additional layers of conflicting triggers and responses, and it only gets worse. Conrad Ferdinand Meyer will rust on new foliage nearly as soon as it unfurls most years and can’t be sprayed. Chemicals applied to Rugosa foliage will cause it to yellow and fall without fungal attack, yet without them, the fungal attacks are nearly a given. Hybrids from him are almost as bad in many instances. Tamora, though drop dead gorgeous, when she’s gorgeous, is as rusty here as Simplicity, as are the others bred from Meyer. I haven’t encountered a sufficiently distant descendant of his to break that reaction.
Take Tamora out of this zone 10a environment and put her in zone 9a with its greater aridity, hotter summers and colder (by just a bit, but colder) winters, and the reaction is tremendously reduced. Meyer, Lipton, both Roserie’s and most other Rugosa hybrids in the zone 9a gardens behaved quite badly. Rugosa itself was far less inclined to contract fungal issues in zone 9a. There were more natural triggers to shed the foliage once sufficiently senile combined with greater aridity to prevent infection. Dry the climate out more and increase the extremity between summer and winter, and it appears they behave much more as historically expected. Level it all out, and they are miserable.
Add immature plants with their undeveloped immune systems; evolutionary vertical resistance (no horizontal resistance was necessary nor really possible, partly due to geographic isolation); over crowding in many gardens with artificial obstacles to air circulation and increased humidity from transpiration and irrigation; higher nutrient levels, often much higher than necessary and frequently sufficient to force growth far past the efficiency of the plant’s “instructions”; to the “confused programming” artificially bred into the plants, often half of which contains far too much inbred material, to the wrong climate, wrong plant and it’s Zazu Pitts, a nervous break down looking for a place to happen.
