I did a brief search here but I couldn't find anything that quite looked like this:
 
   


It looks like someone wiped them with really cheap terrycloth kind of material, doesn't it? Like microfibers or tiny, dusty cobwebs. 

I've never seen this before. It's on each of six cuttings and it grows all over the stem. It rubs off into nothing as soon as you touch the cutting, making it look perfectly clean.

I rubbed the cuttings with hydrogen peroxide once and then with rubbing alcohol a few days later. It grows back within a few days so I'm guessing it's a kind of mold.

I've tried putting them in different places with different levels of ventilation - my most current trial is just with way more ventilation that I would normally use. 

What do you think?

Thanks

Looks like mold to me.  I would try slightly drier rooting material and a little ventilation.  I hear that some people use a 10% bleach solution on the cuttings to kill mold.

Sorry, didn't see your comment about ventilation.  I am having slightly more luck rooting in ProMixHP than I did with the perlite, if that helps.

It looks like mold to me also and I've had this on a few of my cuttings before. When you used the hydrogen peroxide did it bubble up a whole bunch right around the node area? Whenever I've seen extra fizziness after dabbing on the H202 it's usually a mold(or some other type of yuck) so I try lightly (like SUPER lightly) scraping off the mold off and 9 times out of 10 I've been able to get the cutting through to roots.. It seems afterwards mold is much less of a fight when they are out of the humidity bin.. I've used the 10% bleach solution and physan as well and both really help a lot, but still my favorite go to has been the peroxide as of late. Ventilation sounds like a great suggestion as well & Just keep reapplying the h202 if it comes back unless you know for sure the cutting is a goner (no green when scratched). I'm still a noob myself though, so hopefully someone else will come along with an exact diagnosis for you too I hope! Good luck and keep us posted! :)

Ps Maybe be careful using the rubbing alcohol, I did read somewhere that use of rubbing alcohol may burn the cutting out before it even gets started.. So if you really want to use it, I'd at least dilute it first.. Just my noob 2cents though! Lol

Yup, that looks like mold.  Might want to try and drop the humidity levels a bit too.

It's mold. Spray it with 10% bleach solution.

Thanks, all. 

I wish I could remember how the peroxide worked out - it's been about a week or so since I last tried it. Thanks, though.

I just hit them a mist-sprayer with filled with a mix of 10 g bleach to 90 g water and have stored it with better ventilation.

Here's hoping for good news.