Treating Nepenthes Leaf Rust

[theplantman]

Hi guys! I suspect that I have a maxima that is beginning to show rust spots on the lower leaves. Upper leaves are fine and the thing is growing like mad (5-foot-long vines), so I will do some feeding to confirm it's not nutrition because I haven't fed in about a month.

Anyway, I'm looking to see if anyone:
(1) has a formal identification of the pathogen responsible for what we'll call "Nepenthes Leaf Rust"
(2) has succeeded in using chemical control for this (if so, I'd love to hear what brand/active ingredient)
(3) has nonchemical, cultural tips for preventing this from occurring and how to prevent spread
(4) does this rust have other host species (some rusts do, like cedar-apple rust)

Perhaps if we can get enough high-quality information and photos out there we may be able to turn this into a sticky or ICPS article? My nice camera is having battery issues and I'd love to show y'all what the brown spots look like but unfortunately won't be able to.

 

[Whimgrinder]

(1) has a formal identification of the pathogen responsible for what we'll call "Nepenthes Leaf Rust"

I have been informed by more than one authority on the genus that Cercospora is the pathogen. It isn't a Rust, per se.

(2) has succeeded in using chemical control for this (if so, I'd love to hear what brand/active ingredient)

Propiconazole will keep Nepenthes free of the disease if applied regularly. I question the merit of chronic application of any fungicide for this purpose, however. (I hesitate to call it a "disease" since you can clearly see in many photos documenting in situ specimens that plants are commonly infected with the pathogen, and yet it has little impact on the plant health). The last time I sprayed any of my plants to suppress Cercospora was over a year ago. I found that creating an optimal environment limited how much and how often "flushes" of the disease occurred, and now I see it only on well-aged foliage and the amount is generally minimal.

(3) has nonchemical, cultural tips for preventing this from occurring and how to prevent spread

The same authorities that informed me of its identity also indicated that the pathogen is thought to be systemic through pretty much any and all plants (some species more than others -- more on that in a moment), and so the notion of it "spreading" is somewhat artificial. It seems likely that eradication of it from a collection is close to impossible (fungicides suppress the disease but they won't eliminate it from a plant once it shows symptoms) and it is probably present in plants from a very young age onward.
As no doubt many growers have observed, I see a conspicuous increase in the "rust" marks on certain plants when light levels ramp up in spring and through the summer. Most notably, N. robcantleyi is subject to getting very "rusty" when exposed to unfiltered sunlight during the brightest parts of the year. If I move the species to a location that is protected by shadecloth, the rust markings are greatly diminished or just don't happen at all. (On new growth, that is; leaves that have marks on them do not recover their unblemished state) I have also noticed that many N. spectabilis hybrids are quite prone to Cercospora infection. There may be others that are far more susceptible than average, but these two species stand out for me as being highly likely to get badly marked.

(4) does this rust have other host species (some rusts do, like cedar-apple rust)

Not that I know of, but without knowing the exact species of the pathogen, (and I don't) I can't say for sure.

 

[theplantman]

Thanks for the feedback, Paul. I was hoping you'd be one of the people to chime in. I wish I could take photos. Right now it's just faint brown spots. Because they are faint and generally unfuzzy, my hunch is that it may not be a pathogen. I have been examining my reference books and photos in detail and do not perceive any of the ringed, circular lesions that seem common with Cercospora.

The plant is reaching above my CP bench and I am encouraging it to climb into greater light/heat. I suspected at least in part that heat and light may have had something to do with it. Whether by increasing growth rate/food demand or somehow affecting photosynthesis and causing photosynthetically "dead zones" where I am seeing the brown spots. I provide no shade and it would be tough to do so because I'd also have to shade the Drosera, Dionaea, and Sarracenia collections. It's starting to dangle pitchers everywhere and look really impressive too. Up until this week the leaves didn't turn pale or give any other signs the plant was receiving too much light.

I think I'll try getting it fed, then getting it out of the light. If neither works and it becomes what I can characterize as "severe" I have the option to take a sample to a plant pathology clinic for diagnosis and recommend a check for Cercospora. I might be able to find out with certainty whether I have Cercospora, nothing, or something else entirely.

Thanks for your input!!

 

[Whimgrinder]

Kevin,
Sometimes, the markings are just a feature of normal leaf senescence. It isn't always easy to tell which is which, as the Cercospora (if in fact that is part of the package) generally affects only matured/aging foliage.

I would certainly encourage lab testing for the pathogen, since it would be nice to finally put to rest this oft-quoted notion about it being a true Rust, so people don't go around banishing Hollyhocks in fear of spreading the contagion! ;-)