Dahlia: Leaves have lost green color

Discussion in 'Plant Pests, Diseases and Weeds' started by Nadea, Apr 2, 2015.

  1. Nadea

    Nadea New Seed

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    diseaseddahlia357x500.jpg
    What on earth has happened to my Dahlia? It was growing vigorously and then it started to diminish instead of grow. Leaves turned yellowy and crisped around the edges. The shop keeper told me to put some fungicide on it, but it did nothing. The only thing that has helped is whacking it off and letting it grow up again from the main stock. The tubers were very fat, much bigger than when I planted it. I thought that was strange. I was going to throw out the whole plant, but when I saw that I decided to replant it to see what would happen. It's growing again. Any ideas? Is it mineral deficiency? Wrong soil type? Potting soil is dodgy over here. Not sure what I've picked up. It's either in Chinese or German.
     
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  3. purpleinopp

    purpleinopp Young Pine Plants Contributor

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    Hi! It's hard to say much from one leaf. If it's being kept too moist, that could do that. Is this plant inside or outside at this time? If outside, how cold is it getting at night? Would you be able to add a pic of the whole plant? If you have the ability to put this in the ground for summer, it should be much more carefree that way, but probably still need staking.
     
  4. Riccur

    Riccur Seedling

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    Wouldn't an absence in sunlight do this to the plant? Is it in direct sunlight often?
     
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  5. purpleinopp

    purpleinopp Young Pine Plants Contributor

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    Yes, if it's inside, it's likely in need of more sun.
     



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  6. S-H

    S-H Young Pine

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    My guess is that the soil is somewhat deficient in minerals, mainly iron. This is very common in a rooftop garden, as earthworms which otherwise (at ground level) can easily replenish the soil - Can't climb up buildings to do their job. Which is why the nutrient content of the soil needs to be kept an eye on. In my experience it is often iron deficiency, which makes the plant very susceptible to all types of disease.

    We often get confused, as we are too focused on curing that particular ailment - Yet we often forget the basic rule of gardening is that if your soil is rich in minerals, then plants themselves will automatically become strong enough to fight off any pest and/or infection! Anyhow, that's what I think could be the case over here. However I could be wrong, as I am no where near as experienced as some of the other members over here. But leaves turning yellow is often the result of iron deficiency, provided of course that the plant is getting enough sunlight. Otherwise, if it is not getting enough light, then even if the soil is rich in iron, we again will see this symptom...

    Anyway, the climate of Hong Kong is very similar to Karachi, unbelievably hot, very sunny at times, and humid beyond measure too! So I still think that it's the soil, as this is how I solved my problems. Only difference is that Hong Kong gets lots of rains too, while in Karachi we sometimes don't get any major downpour for 3 to 5 years straight! Still, the issue of soil depletion in containers on rooftops is often the same everywhere...

    Hope this helped, (and did not confuse you further)! :stew1:

    By the way, grow some garlic in small pots, and place them between all your other plants. As not only do they naturally repel aphids and mealybugs, but also won't let any fungus infection spread in the soil.
     
    Last edited: Apr 9, 2015
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  7. Brisbane Trees

    Brisbane Trees Seedling

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    It could indeed be iron deficiency. If so, it would be appearing first on juvenile leaves. Just as likely are nitrogen and manganese deficiency or a fungus.

    I suggest you listen to everyone here by giving it a little more sun, applying a balanced fertilizer in moderation and ensuring you don't water the leaves.

    Edit: I just noticed the older leaves look more shriveled. I'm thinking it's a nitrogen deficiency.
     
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  8. Nadea

    Nadea New Seed

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    No, it's not inside. It's been outside since I planted it. I chopped it back and it's doing great now. Fingers crossed. It's growing very well, and very green. It's in the same pot in the same place on the patio. It's warmer now. Maybe that has something to do with it?

    I may have over-watered it, :worried:, but it's doing very well now. Our major Spring rains haven't arrived yet. S-H Young Pine is right. Our summers are horribly hot and humid. I will try not to water the leaves, but when Mother Nature gets to work and sends the rains, she's not discriminatory about where to put the water! It's getting more sun for longer now as the sun has risen above the buildings.

    I am giving it fertilizer on a regular basis. Maybe I wasn't giving it enough at first.

    My garden is on the rooftop so no option of putting it in the ground. I know that would be an ideal situation!

    Thanks everyone for your help! Much appreciated.
     
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  9. Brisbane Trees

    Brisbane Trees Seedling

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    I should mention, mulch is great fertilizer. In nature, plants get all their nitrogen from sources other than the mineral part of the soil. Humus, broken down mulch, is an important part of that.

    When green waste starts breaking down it actually uses nitrogen, so it's good to have a compost bin, then add the broken down compost to the soil.

    In the case of your plant, though, it really needs a foliar spray as a quick injection of N. Well, I should have said that 2 weeks ago, but if it looks now like it did then, I'd do it now.
     

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