Mold? What to do?

This has occurred because you covered the wound. In future, let any wound open to the air so it can dry and "scab" over. Your plant will grow just fine with a broken stem. The main thing is to keep it dry. Sometimes you can wrap it tightly with grafting tape and the wound will heal, but leaving it to air dry works fine and is easier. For treatment, follow the others advice regarding the sulfur.

If its only on the split you can save it. Look at week 13 of my grow- I split the main stem too. It happens. U want horticultural Lime Sulfur. Go to garden center and get some today or tomz. Make it up at HALF STRENGTH (50%) and get a clean small paint brush and ONLY brush the 50% strength solution onto the area that has mold. U may need to repeat this 2 or 3 times over a 7-10 day period. But aside from the time u paint the wound- and dont go over board, just a nice thin layer is fine....make sure you keep the wound totally dry. Dont mist it or get nutes on it. As ive explained about fixing splits, u need to fix it super fast and use tape to hold the wound back in plane AND keep out infections and bugs. Bugs love to burrow in thru stem damage and thats when U see huge main colas just suddenly die off for no reason sometimes. Bugs got in. Yours doesnt look too bad at all. Just treat it fast as time isnt your friend here. keep it dry til you do ok.

If it's only in 1 plant, me personally, I wouldn't take the risk with my whole crop if I wasn't 100% sure what it was and that it won't spread. You shouldn't get mold from a split. And if you are you might have poor ven or high RH. You have a lot of healthy plants, me I wouldn't risk it unless I knew what it was. And if you increase ven and it spreads now. Best to cut out a cancer than give it a chance to spread. Good luck pal.

Hello. I use agriculture sulfur on all my plant cuts, scrapes and toppings. You can get at most garden centers and at the pharmacy for people grade sulfur. It is antifungal so mold won't be a problem. It soaks up sap. A real plant healer. Don't get too much on the soil, but the plant uses sulfur to grow ( please google that) Hydrogen Peroxide diluted down to 1% will knock it out too. Plants look good. Chuck.

Keep humidity low the rest of grow. Clean everything when done.

No question in my mind this mold my friend you'll need to handle this immediately before it starts moving on to other parts of the plant.