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I have a pretty new Alocasia (1-2 months), stays indoors (currently an average of ~20-10 celsius day/night) in a bright room but with no direct sunlight. It started developing those yellow spots on one of the leaves (and only one) and I'm not really sure what this is. I'm watering around every 7-10 days when the soil gets slightly dry. The leaf itself, on the spotted areas, feels a bit mushy and eventually dries out and leaves a hole.

  • What should I do?
  • Any risk to the other leaves?
  • Should I cut it off now or keep it as most of it is healthy and this is the largest leave the plant currently has before springtime (it has a "mother" with 2 large leaves, and a "baby" with 2 smaller leaves)?

enter image description here

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  • When I look very closely at the picture I see a small black shape the size of an exclamation point near one of the damaged areas. Do you see that?
    – kevinskio
    Commented Mar 10, 2023 at 12:44
  • I'm not sure I see that.. Can you mark on the picture somehow?
    – Zach Moshe
    Commented Mar 10, 2023 at 20:24

1 Answer 1

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I think this issue is one or more of two things:

  • overwatering leading to fungus/virus/bacteria
  • thrip

Diseases have a typical growth pattern. When the plant is weakened due to the root zone being saturated with water they take advantage and start growing in areas on the older leaves. You see a light spot in the center surrounded by a halo of dead tissue. Then the dead area grows larger. I see this in the picture above.

I also see what I think is a thrip. See the picture below where I have circled what looks like an adult. The diagnosis can be confirmed by looking at the leaf with a magnifying glass or similar phone app. You should expect to see silvery trails inside the leave where the juveniles live. If the infestation is advanced you may see the nymphs who are pale walking around on the leaf. Adults are dark and the size of an exclamation mark.

If it is thrips they may have come in with the plant or may have flown from some other plant. They cannot be controlled with soap and water or neem oil as the kids live inside the leaves. I suggest:

  • inspect all your plants for thrip. They like Pothos but will eat other plants too
  • cutting back all the leaves that have something and dispose of in a bag right away
  • putting all the plants outside for a month or (if you have warm exterior temperatures) works well
  • blue sticky strips may work for you but did not for me

Thrips are really hard to get rid of and sometimes just throwing the plant out is the most effective control method.

thrip on alocasia

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  • Thanks! I can't see anything moving on the leaves now, but how small exactly can they be? If it should be >1-2mm then I'm pretty sure I've covered all leaves. I moved it far away from other plants just to be sure..
    – Zach Moshe
    Commented Mar 11, 2023 at 10:53
  • @ZachMoshe Thrip are 1 to 2 mm long and when they are disturbed they will fly to new plants. I would cut back the leaf, reduce the water and watch what happens on new growth
    – kevinskio
    Commented Mar 11, 2023 at 13:27

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