Systemic infections usually result in plant death since the plants ability to transport water and nutrients is destroyed. Ivy geraniums usually do not develop severe symptoms and can have latent or unexpressed infections thus acting as a source of inoculum. Be sure that all of your geraniums remain symptom free by scouting them weekly. Sometimes they are clustered around the outer portions of the leaf. These blisters can become corky and sometimes result in leaf drop.
Leaves appear yellow from above when edema is severe.
Control - Edema occurs when a water imbalance causes more water to be moved into the leaves than can be utilized. This water collects and causes the blisters described above. Edema is most common during the spring and fall when soil and air temperatures differ substantially. Provide plants with optimal conditions and reduce water applications to limit development of edema. Bleach phytotoxicity Symptoms - White sunken areas form all over leaf surfaces.