Why do Zinnias always get these spots? TIA!

purpleinopp said:Why do Zinnias always get these spots? TIA!

Hi Tiffany,

That Zinnia foliage disease is Alternaria Blight. Zinnias don't always get Alternaria Blight, only if the soil in their immediate area is infected by the Alternaria zinnia fungus. The fungus is favored by moist conditions.

The fungal spores are spread from plant to plant by wind and splashing water. The fungus survives on infected debris in the soil and on contaminated seed, where it can also cause damping-off of seedlings.

Alternaria blight can be controlled by spraying with a good systemic fungicide.

ZM

TY for the info! I figured you would know and I was hoping you would see my question.

Contaminated seeds sounds like the culprit. The area in question was lawn for 100 years, AFAIK, until I dug up some grass in '15 and, among other plants and seeds, Zinnia seeds were scattered.

No other plants that happen to be nearby seem affected, and there are no Zinnias nearby that I've noticed, though I'm not sure how one would define "nearby" in regard to the spores (?) of this blight. How far away would I need to go from that spot to have reasonable expectation to grow blight-free Zinnias in another area? Still in my small in-town yard but in the back yard instead of the front, 1/2 mile... farther? Would foregoing Zinnias next year and then trying the following year be a way to get past it?

Not to snub your advice in any way, just the way I roll - I generally don't treat plants for anything, but replace them with something more amenable to the conditions I have available. Are there other plants known to be affected that I just don't happen to have in that area? Knowing that would help me avoid compounding the problem.

Thanks again, so very much appreciated!

purpleinopp said:No other plants that happen to be nearby seem affected, ...Are there other plants known to be affected that I just don't happen to have in that area?

Hi Tiffany,

The Alternaria Blight is caused by the Alternaria zinniae fungus, which sounds very much like it is a disease that is limited to just zinnias. I don't know of any "safe distance" away.

ZM

Thanks for your personal assessment.

For others who are interested, I can't speak for the veracity of the info at these links but it's suggested that after 3 years, it should be gone. Also instructions for sterilizing seeds.

http://www.missouribotanicalga...

https://negreenhouseupdate.inf...

Hey @zenman thank you for the above info.
Can you tell me when to spray fungicide? My seedlings are 2" high, no signs of any problems yet, but every other year usually do have the above blight & mildew. I planted saved seed from last years' crop. And, this is an unusually wet year.
Appreciate any input.

katesflowers said:Can you tell me when to spray fungicide? My seedlings are 2" high, no signs of any problems yet, but every other year usually do have the above blight & mildew. I planted saved seed from last years' crop. And, this is an unusually wet year.

I wouldn't spray until you see a visible sign of a fungus infection. But then I wouldn't hesitate. A systemic fungicide lasts for several weeks. The label on the container should give you some idea about the expected frequency of application.

ZM