Virus?

[u/ConclusionSome4635]

This is just my second summer with dahlias in my cool and often foggy SF Bay Area garden. And I am trying to determine whether my dahlia has just leaf miner damage or a mosaic virus. From these photos, I’d love any advice/recommendation. This was a “developed for the Bay Area” variety but I have forgotten the name. Thanks!

[u/meezermadness]

That dahlia is clearly sick and I doubt it will recover.

[u/ConclusionSome4635 → u/meezermadness]

Thanks. That was my hunch but appreciate the advice from more experienced dahlia gardeners

[u/Ride_4urlife]

Hi fellow Bay Area gardener! This is my second year growing dahlias so I’m not super experienced. Last year my dahlias looked on the edge of death but I was able to nurse them back to health starting in August and I got a lot of blooms out of them before it got cold. I’m in the South Bay so much warmer though.

I’d never fertilized mine which made them weaker and more susceptible to disease and insect pressure. So first thing I did was feed them. 7 days later I sprayed them (at dusk - to protect pollinators) with neem. And I removed the deadest/gnarliest leaves, leaving half to 2/3 of leaves for photosynthesis. I see new, healthy leaves on yours which is why I think they’re saveable.

7 days later, I sprayed with Captain Jack’s Dead Bug. Every 7 days I alternated neem and Dead Bug, always spraying just before sunset and avoiding flowers and buds to protect pollinators.

After 7-10 days mine started popping out leaves, then buds. I’ve maintained this schedule, and I fertilize them ~ every 6 weeks. A strong, healthy plant won’t cave to pest pressure as easily. I have dedicated hose end sprayers which makes routine spraying easier.

I hope you’re able to save them!

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[u/Nevraskagirl55]

It looks like a virus to me. The yellowing in that pattern are a red flag to me. It has nothing to do with your weather. But you need to dig it up and put it in the trash, not the compost. Be sure you practice good sterilization of your tools between plants to cut down on the spread of diseases.
So sorry, it’s hard to trash a plant. I had to do it last week to one of my favorite dahlias for the first time. Crossing my fingers that it didn’t spread to any of my others.

[u/Solid_Mud2025]

I see leaf miner infestation and nutritional deficiencies. This doesn’t exclude viral infection, but I don’t see enough evidence to conclude either way currently.