Hi guys,
I have some cuttings in rockwool cubes which are about 4-5 weeks old and most are healthy but around the base of some of the cuttings and on the lower leaves there has formed a sticky, tarry like substance. The affected cuttings are still showing good root systems although they are much smaller that those not affected. I've tried to wash it off but no luck. I am using 1/4 or less nutrient feed with plain water in between times and misting twice daily, and the ph of the water I use is okay. I think it's a build-up of nutrients but could be wrong. Is this stuff harmful and how do I stop it in future.
TIA

Sounds like algae mate and is quite normal when the block is exposed to light

Cover the block with a bit of reflective material and it will keep the lower leaves off the block

I would also stop misting the cuts aswell mate as there is no need tbh unless your humidity is really really low

You can end up leeching the goodness from your plant if you carry spraying

Owd

Many thanks as usual M8 - I'll stop misting them - so just water the cubes then?
Cheers

Foliar feeding is a useful way of giving your plants a boost, but you should not use it too much, because the plant will get used to getting its nutrients from the leaves instead of developing its root system.

Use it as a treat for your girls, but no more than twice a week, just before the lights go out (water drops under a light act like a magnifying glass and can burn your girls leaves)

Once you pot them up, try misting with 1/4 strength nutes, a little wetting agent and a root stimulant such as rhizotonic. I occasionally add a bit of nitrozyme as well - the plants will go mad, but they need a root structure for it to work properly - and as I said, only do it about twice a week

Algae is fairly harmless and wont affect your girls unless it spreads over the roots - as Owderb said, limiting the light will stop it forming, but its nothing to get too worried about