Leaf drop on yuzus, apparent mystery pest

Discussion in 'Citrus' started by WA Adam, Nov 13, 2018.

  1. WA Adam

    WA Adam Member

    Messages:
    4
    Likes Received:
    0
    Location:
    Puget Sound, Washington, US USDA Zone 9a
    Hello,

    I sprouted a lot of yuzus late last year from seed and they're now going through their first winter outdoors. I've kept them in a greenhouse, and plan to bring them under cover if we have a hard frost, just since their so young.

    However, my main issue is that they all seem to be losing leaves and quickly. See here: Imgur: The magic of the Internet

    They had suffered previously from spider mites this summer, but regular application of soapy water and mechanical removal brought that under control months ago. And with that, there was a definite pattern on the leaves of feeding marks.

    This time, there are no such marks. Instead, the leaves are simply falling off. The only sign I can see of any predation by insects is these small brown patches on the leaf undersides:

    Imgur: The magic of the Internet

    I very occaisionally have seen some webbing near the stem a few small leaves suspended from them. Immediately after seeing the leaf drop and that webbing, I hit all my citrus with soapy water sprays, then a homemade horticultural oil spray (mineral oil + soap), then sprayed them all with rubbing alcohol for good measure. Yet the leaf drop continues.

    Strangely, some of my other citrus seem less affected. I have a few Taiwanese sour oranges (Citrus taiwanica) which are largely unscathed. See photo here: Imgur: The magic of the Internet

    Any advice on what I should do? Part of me wonders if I've dealt with the insect issue and now I'm just seeing impact from the cold now. But the leaves keep dropping and it has me concerned. A similar thing happened to my Meyer Lemon last year and it died completely. I thought it was just that plant, but now all my yuzus are acting this way.
     
  2. WA Adam

    WA Adam Member

    Messages:
    4
    Likes Received:
    0
    Location:
    Puget Sound, Washington, US USDA Zone 9a
    After some thought, I'm now wondering if my repeated treatments of soap sprays and horticultural oil might be the cause of the leaf dropping. I also sprayed an olive tree and a perennial yam and they're also showing similar symptoms. Perhaps my soap and horticultural oil mixtures were just too strong?
     
  3. Junglekeeper

    Junglekeeper Esteemed Contributor 10 Years

    Messages:
    5,987
    Likes Received:
    608
    Location:
    Vancouver BC Canada
  4. WA Adam

    WA Adam Member

    Messages:
    4
    Likes Received:
    0
    Location:
    Puget Sound, Washington, US USDA Zone 9a
    I'm now 99% sure the damage was from the soap I used and possibly the strength of the horticultural oil I used. I looked at the weird spots/pitting on the leaf undersides in my dissecting microscope and it looked more like something had corroded the leaf, so to speak, rather a wound that was biological in origin.

    I gave all my plants a spray down with water to help wash off the residue on the leaves and the leaf drop has so far stopped. I have a few larger trees that had had far less leaf drop (and which were sprayed less).

    Assuming it was some sort of pest, they don't seem to be moving from the more impacted plants to the less impacted one. I had similar symptoms in Meyer Lemon from last year, and only sprayed it, and funnily enough, only that tree got worse and eventually died. So that makes me doubt even more it was pest-caused.

    So it looks like I caused the majority of my citrus collection to largely defoliate. Oops! But I learned my lesson and I'm hoping they'll all bounce back next season.
     
  5. Junglekeeper

    Junglekeeper Esteemed Contributor 10 Years

    Messages:
    5,987
    Likes Received:
    608
    Location:
    Vancouver BC Canada
    You may want to consider switching to a commercial insecticidal soap. I buy the concentrate and mix the solution myself as it's much more cost effective.
     

Share This Page