Powdery Mildew on Crassula

Powdery mildew is often one of the easiest plant diseases to identify. The light colored fungal growth is usually easy to see on plant surfaces, and the dusty/powdery spots and patches are a tell-tale sign of powdery mildew. However, in some cases symptoms may not be so obvious. One recently seen example is powdery mildew on crassula. At first, obvious scabby and corky leaf lesions were observed. However, at closer inspection you could see the white fungal growth of powdery mildew. It is not uncommon to see scablike lesions on succulent plants—if you see these symptoms, look closer for powdery mildew.

Powdery mildew favors moderate temperatures and high humidity. Do
whatever you can to keep humidity low (less than 90%) including well timed irrigation, good plant spacing, and using fans and ventilation.

If necessary, numerous fungicides are labeled for powdery mildew management in greenhouses. Use different modes of action in rotation and make sure to read the pesticide label. Follow instructions regarding application, rotations for the prevention of resistance, plant safety, and all other precautions.

Be sure to clean greenhouses between crops, eliminating infected pet plants, carryover plants, plant debris, volunteer plants, and weeds.

Source: e-gro.org