St. John’s Wort (Hypericum)
Symptom Cause  
Lower foliage looks burned
Dog Urine
Leaves covered with white powder
Powdery Mildew
Plants look sickly
Root Knot Nematodes
Powdery spots on leaf undersides
Rust (on plants)
Cottony masses or bumps on twigs, leaves yellow, drop; bumps on leaves and stems; sometimes sticky leaves
Scale Insects
Foliage damaged in winter
Winter Burn