Geranium business hit with bacterial blight

Brian Hudelson, UW-Extension, Senior Outreach Specialist
Plant Diagnostic Lab, Department of Plant Pathology
UW-Madison College of Agricultural and Life Sciences


Brian Hudelson explains bacterial blight in geraniums and what gardeners should do if they suspect their geraniums have been hit by blight.


3:07 – Total Time

0:17 – Description of the geranium blight
0:33 – Disease symptoms
0:58 – Affect on greenhouse business
1:45 – How the blight hit Wisconsin
2:23 – What to do at home
2:57 – Lead out


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Sevie Kenyon:
Describe for us this bacteria that you’ve found in the geraniums.

Brian Hudelson: It’s a technically called Xanthomonas hortorum pelargonii it’s a very specialized bacterium that will attack, lots of times our annual geraniums, but will also go to our perennial species of geraniums as well.

Sevie Kenyon: And what does the disease look like?

Brian Hudelson: Usually annual geraniums, which we call zonal geraniums, we see angular leaf spots…so you’ll see a dead area on a leaf that has kind of straight edges and then a yellow halo around that. And the bacterium follows the veins back down towards the pedicels and once it gets to the pedicels the pedicels collapse and then you get a blight so the entire leaf will die.

Sevie Kenyon: And what does finding this bacterial blight mean for the geranium business?

Brian Hudelson: My recommendation, typically, is to take plants that are showing symptoms and destroy them, because you really cannot cure the plants of this particular disease and I also tell folks to continue to monitor any plants that are not showing symptoms, because the bacterium can actually hang around on the leaf surfaces without causing symptoms right away. So, we sometimes will see a delay in symptom development, so they have to be very very diligent and watch for subsequent symptom development and destroy those plants as well. And this can wipe out an entire geranium crop for a greenhouse. The grower that submitted the samples to me from the greenhouse had seven different varieties, all of which tested positive for this bacterium. And then basically that grower had to eliminate their geranium production for the year.

Sevie Kenyon: Brian do you have any indication how this got in to Wisconsin?

Brian Hudelson: We’ve been getting reports that there was a supplier of geranium cuttings that unfortunately had a problem with the bacterium and didn’t know it and had sent out cuttings to smaller greenhouses and that’s the typical way of producing geraniums is to buy the cuttings from a large supplier… and it’s an easy way—unfortunately—to introduce a problem to many many different “mom and pop” sort of greenhouses, and so they brought the bacterium in with the cuttings that they then rooted and grew up and then as the plants matured the populations of the bacteria got large enough that symptoms started to show on the plants.

Sevie Kenyon: If a customer gets one of these things home, what should they do?

Brian Hudelson: Basically, destruction of the plants, so I would suggest really basically put them in a landfill is probably the best way to get rid of them. You could try to compost them although you do have to worry this bacterium tends not to survive in straight soil. It does not survive typically away from plant debris or live geranium plants. If you can get that material decayed and with composting if you’re heating things appropriately, you could probably get rid of the bacterium that way. But, my typically recommendation is to bag them up and landfill them, get rid of them that way.

Sevie Kenyon: We’ve been visiting with Brian Hudelson, Plant Diagnostic Lab, University of Wisconsin—Madison, in the College of Agricultural and Life Sciences, Madison, Wisconsin and I’m Sevie Kenyon.

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