Last year, I learned something new about euphorbia: they are prone to mildew and have their own particular species of mildew which only attacks them and not other plants. Normally when we think of mildew, we think of damp conditions but euphorbia-specific mildew doesn't require extra humidity. It can be treated with ordinary fungicides but it always recurs and the mildew soon develops resistance to an antifungal unless you use different products every time. So I am not that motivated to keep spraying it and it is better prevented by improving growing conditions for the plant so that it is less susceptible. When I first brought this Euphorbia globosa home it developed a major mildew attack and I thought it would die.
I sprayed it with copper spray and moved it inside and it improved but I thought that the house was too humid because the mildew would recur every time I watered the plant. Outside, the mildew was less but never quite gone. It has had a bad outbreak again recently and I think that it was caused by a combination of cold nights and too much winter sun. This is my only Euphorbia that gets affected by the mildew so I still need to figure out exactly what this plant needs to make it less susceptible. The mildew won't kill it but it always attacks the flowers badly. This is the original 'Goldilocks' plant. One day, I will figure out exactly what will make its growing conditions "just right".