I was propagating white sage via potted cuttings which had made it through the most crucial/risky period and seemed to be establishing roots. They had been getting white fuzzy mold/mildew spots for a few weeks and I had been removing affected leaves with seeming success. I went out of town for 1.5 weeks and it seems the mold has taken advantage of the water stress, infesting most every leaf on the plant. At his point is there anything I can do for the fully infested ones or should I just get rid of them? There's one plant that only has a spot or two of mold that I would like to save if I can, but is it even possible to remove the infected leaves without spreading the spores everywhere? What other natural remedies could I use to keep the mold from returning?
It's also notable that I have seen two leafhoppers over the last month or two so that could definitely be weakening the plant but based on the scarcity of sightings I think those are more likely to be isolated occurrences than full infestations.
What I did wrong:
Pots too close together
Should have thinned the leaves more
What I've been trying so far:
Bottom watering Removing affects leaves (trying my best not to spread the infection)
Does it look like powdery mildew? I've read about using dilute milk to treat powdery mildew, though I didn't have problems with it myself this year and so didn't try it. There are lots of web pages about that.
Hopefully I'm not too late to help... google "powdery mildew", it sounds like you've got an infection. Powdery mildew is pretty easy to control if you catch it early. I have two go-to remedies.
Milk. Yep, it works. I have used a 10% solution with a bit of soap as a surfactant with good results, even on squash that were literally white with the stuff. It will NOT make the infected leaves better, it will stop the infection from progressing. I now use kefir, which seems to be more effective. I keep some grains in a 1/2 gallon mason jar just for the garden.
Neem oil. This is my favorite because it works so well for so many issues. Use the cold-pressed stuff, NOT the cheap stuff you can get on eBay. I use 1 oz/gallon, plus 1 oz/gallon of soap (Dr. Bronner's )
The key is to spray a few times, 2 days apart, and get complete coverage of the topside of all the leaves. This way you get all the spores that are about, including the ones you can't see, busy germinating. For the record, I haven't seen any correlation between plant stress and PM infection. It seems to pop up when conditions favor it, around here that's hot, dry and windy.
Companion Planting Guide by World Permaculture Association