Problem-Solving during growing season forum: Is this mildew?

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Views: 23, Replies: 4 » Jump to the end
Dec 27, 2022 4:40 AM CST
Hi all - grower in sub tropical Australia here. What do you make of this stuff under the leaves of my delightful Cafe au Lait? It was a strong and vigorous plant and suddenly it has taken a turn for the worse... What should I do? In the top photo it almost seems like there are little black lumps on the plant leaf... Do you think that whatever this is could spread to my other dahlias?

Further info - I grow my dahlias in pots, I don't water from above, this guy is out of the way of rain but may have got some, fed sometimes with a low N fertiliser.

Thumb of 2022-12-27/LadyDanika/b2e4da

Thumb of 2022-12-27/LadyDanika/849063
Thumb of 2022-12-27/LadyDanika/15f92f
Dec 27, 2022 8:42 AM CST
Name: Jane
Southern California Zone 9/10
Hi LadyDanika....Welcome! Those little black dots remind me of the spider mites I would get in the heat of summer. Take a magnifying glass and look to see if they move. Good luck.
"In joy or sadness, flowers are our constant friends"-Kazuko Okakura
Dec 27, 2022 9:39 AM CST
Name: Ted
We enjoy breeding new dahlias!
Generally, low nitrogen fertilizer is high phosphorus and potassium fertilizer and dahlias need more nitrogen and less phosphorus.
We like to place a sign on our porch that says: We are in the garden. Really, we are always in the garden.
Dec 27, 2022 4:53 PM CST
Name: Steve
San Diego
Commercial cut flower grower
It looks like there could be a few things going on here (is it ever just one thing). Are the symptoms only on the bottom few sets of leaves?

When I see container plants with leaves yellowing and turning brown on the edges I think of root stress. Both, plants that are getting too much water, and plants with "too hot" roots, can show these symptoms. If the containers and plants are not too large I would try to gently "tap" the root ball out of the container to examine the roots. The roots should look white and the soil should have air spaces and not be waterlogged.

You could also have some thrips or mites feeding on the plants but I can't tell for sure at this resolution. You will have to examine the leaves with a magnifying glass to verify their presence.

Another possibility is that these are the very bottom leaves on an older plant and it is normal. Older leaves that are dying can show all sorts of strange symptoms.

For now, if it is only the lower leaves showing symptoms, I would remove the symptomatic leaves and verify the root zone is in good shape.

[Last edited Dec 27, 2022 4:57 PM CST]
Quote | Post #1411777 (4)
Dec 27, 2022 5:01 PM CST
Thank you so much SteveM, Teddahila and Flowernut!

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