Knowledgebase

Mosaic virus #876790

Asked July 11, 2024, 9:28 AM EDT

Hello, I live in Astoria and last year I my garden became infected with mosaic virus necessitating destroying about ½ of the plants. This year i dumped out all of the soil in order to make a fresh start, and, so far. so good. However, I’m a bit nervous. My husband loves hollyhocks and has propagated them by scattering the seeds from each year’s plants around our property so now there are quite a few. This evening I noticed that about 1/2of them appeared to have condition that looked suspiciously like mosaic virus in the lower part of the plants (See attached pictures.) Here are my questions: 1. Based on the pictures, do you think the hollyhocks have mosaic virus? 2. If so, should I pull the affected plants out? The closest one to the vegetable garden is 30’ away. Thanks!

Clatsop County Oregon

Expert Response

Hi Kate,

Sorry to hear that you've been having mosaic issues and now hollyhock issues as well. The symptoms on most of your leaves and the small lesions on some of the stems make this disease look more like hollyhock rust to me, which is fairly common. You can read more about hollyhock rust in this extension publication from UW Madison and see available control measures in our PNW Disease Management Handbook (chemical controls marked with an H are available to home gardeners).

However, I don't feel that I can fully rule out a mosaic virus, such as the zucchini yellow mosaic virus that hollyhock is susceptible to, based on your photos. I'm including our statewide Extension Plant Pathologist, Jay Scheidt, as a collaborator on this question in the hopes he can offer a more conclusive diagnosis based on your photos.

Either way, your safest bet is probably to remove the infected hollyhocks. If it's rust, spores will develop that can spread via wind and overwinter in affected plant debris. If it's a virus of some kind, it will likely spread via an insect pest that could transmit it to other areas of your garden.

Please don't hesitate to reach out to me with any follow up questions.

Best of luck,

Shannon Rauter

Master Gardener and Small Farms Program Coordinator

Clatsop County Extension Service

Shannon Rauter, Master Gardener and Small Farms Program Coordinator Replied July 16, 2024, 4:31 PM EDT

Hi Kate,

Please see this response from Jay Pscheidt, our statewide Extension Plant Pathologist:

"The image is not quite close enough but I think you are correct about rust. It is a major issue everywhere. Some of the spots look more like holes which has be thinking insect such as Hollyhock weevil: https://pnwhandbooks.org/insect/hort/landscape/hosts-pests-landscape-plants/hollyhock-alcea-rosea-hollyhock-weevil

I do not see a mosaic on these leaves and do not suspect a virus."

Based on Jay's more accurate diagnosis, you could leave the hollyhocks in place if you haven't already pulled them and your husband is passionate about keeping them. However, if they are harboring rust or the hollyhock weevil, that will likely spread over time. You could try pursuing chemical methods, but it is likely too late for those to be effective. It is up to you whether to pull them out depending on how much you worry about your other hollyhocks being affected as well.

Hope this helps!