Help! My African milk tree isn’t doing well. I already removed one stalk because it turned black spotted and mushy. I carefully repotted what was left (and appeared healthy) and moved it to a room without a humidifier. It’s getting a lot of love from my grow lights and is not overwatered. I also treated with neem oil. But now there’s a black spot coming in on yet another stalk, near the base. (So far still firm— not mushy). Any ideas as to what’s wrong and how to treat?