Wild geranium - white film

Asked June 25, 2020, 4:20 AM EDT

There is a white film growing on the stems of two wild geranium/cranesbill (geranium erianthum?) that I'm growing in pots. Is this normal? It seems to start at the crown and be working its way up the stems, but there are some isolated spots higher up on the stems. The white film is also on the nodes and right at the base of the leaves, but not on the flowers, buds, or topsides of the leaves. The plants are still putting out new leaves and blossoms. A smallflower columbine in a pot between the two geraniums is completely unaffected. I investigated a nearby roadside patch of wild geranium, and nearly all of those plants had various states of the and stuff: from extensive spotting and film to a thick white fuzz uniformly covering the whole stem. But the stuff was *not* growing on the grasses or vetch that were also growing in that roadside patch. I can rub off the film with a fingernail to expose a bruised and discolored yellowish-brown stem beneath, but the affected stems are still standing upright, supporting the leaves and flowers. The stuff does not leave a residue on my fingers. I did used Fungicide 3 for a few weeks, which seems to have caused some leaf drop on all three plants , and most noticeably on the first plant, which I sprayed more aggressively (Far left plant was affected first, a few weeks before the one on the far right).

Anchorage Alaska

1 Response

This looks like powdery mildew on the stems. This is normal in wet/humid conditions, and can sometimes be improved by increasing air flow. There is good information about this issue at https://ag.umass.edu/greenhouse-floriculture/photos/geranium-powdery-mildew#:~:text=The%20disease%20is%20easily%20recognizable,%2C%20wither%2Cand%20defoliate%20prematurely.