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My 18-month-old avocado tree has had a fungus a couple times, which I have successfully treated with a generic fungicide spray for ornamental plants (Penconazole, Dodine). It lives indoors year-round near a south-west facing window, and gets watered every 9 days.

I'm not sure if its most recent infection was a fungus or something else, but I thoroughly sprayed with the fungicide because about half the leaves were dying. Now ALL of the leaves are dying, and I'm wondering if the problem was the fungicide, or if it simply didn't work at all.

The first picture is an infected leaf before I sprayed, is this a fungus? The second picture is of one the last still-attached leaves two weeks after I sprayed, is this still a fungus, or did I cause the problem with my spray (or something else)?

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I have a new batch of tiny leaves now growing, so I want to nurse them to health and avoid the same mistakes.

Update: here are some of the new baby leaves, that are already clearly unhealthy. Is this fungus, or something else? Some batches of new leaves look very healthy, but some are already half-brown like these. enter image description here

Thanks in advance for any tips on how to nurse my tree back to health!

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Well if that grey pot is the volume for the root ball you may be testing the capacity of the soil to hold water. The soil looks rather sandy on top, which might be good for drainage but not for holding water. Fast drainage is good for avocado, but watering every 9 days might not be sufficiently frequent, particularly as the plant gets bigger and it depends less on the original pit for support and looks to the soil as a moisture reservoir. I water mine every 3-4 days and the roots are nowhere near filling the pot yet.

Avocado leaves transpire quite rapidly, particularly if the air is dry and in a southern window. My guess is that after watering the new leaves are encouraged to burgeon but the root dries down too fast and the new leaves cannot be further supported, with the consequent dieback. You can test this by removing the root ball from the pot and examining the surface of the ball. If highly populated with roots (the root ball will willingly come out in one solid mass) then it needs a new larger pot with good soil and then it can continue to prosper.

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  • Thanks for your reply. Underneath the top inch of sand to keep out the tiny flies, it's actually just generic multi-purpose gardening soil. It drains okay, but the plant has had a fungus a couple times, so I thought maybe the problem was root rot, so I reduced my previous 7-day watering cycle to 9 days. Could the solution really just be to replace all the soil with a lighter potting soil, and water more frequently? Could that help with the probable fungus on the leaves as well?
    – Animik
    May 1, 2020 at 13:42
  • In that case there is less soil than I thought and reinforces my impression. My suggestion (no doubt you will have others) is to pot up to a larger pot, and use your regular potting mix with one part sand to 3 parts soil and boost the watering schedule. With the extra sand you may not need the layer of sand for fungus gnats. Sorry, cannot help on the fungus, never seen it on mine.
    – Colin Beckingham
    May 1, 2020 at 13:50

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