Forum home› Fruit & veg
This Forum will close on Wednesday 27 March, 2024. Please refer to the announcement on the Discussions page for further detail.

Black leaves on pot growing pears

IgrowfromseedIgrowfromseed Posts: 284
in Fruit & veg
Hi I’m seeing these black areas on a few of my pot grown pear trees. Happens in last few days after spraying with diluted washing up liquid. Wasn’t sunny at the time.
«1

Posts

  • DovefromaboveDovefromabove Posts: 88,147
    edited September 2023
    The last photo looks like you’ve made the leaf surface sticky and a mould has set in. 

    Can I ask … why were you spraying with dilute washing up liquid?

    Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.





  • IgrowfromseedIgrowfromseed Posts: 284
    Good question. Seen some greenfly. Would mould not need something sugary rather than washing up liquid?
  • DovefromaboveDovefromabove Posts: 88,147
    Not necessarily … moulds form
    on all sorts of things …and aphids secrete sugary stuff anyway. 
    Far better to have swooshed the aphids off with a jet of water from the hosepipe, or even just brush them off with your fingers. 😊 

    Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.





  • pinutpinut Posts: 194
    I propagate and grow pear trees in containers.

    The only time I have encountered the blackening of leaves was during the advanced stages of pear rust disease. But, your trees don't show any signs of that.

    Let me see if I can duplicate the problem by doing an experiment on my trees.

    Before that, I will need some details:

    What brand of washing up liquid did you use and in what concentration?
    Was the spray bottle cleaned out before filling?
    Was the soil dry, moist, or wet when the spray was applied?
    Over what span of time did the blackening occur?


  • DovefromaboveDovefromabove Posts: 88,147
    Would the weather conditions/temperatures etc at the time of and following applications be pertinent?

    Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.





  • IgrowfromseedIgrowfromseed Posts: 284
    pinut said:
    I propagate and grow pear trees in containers.

    The only time I have encountered the blackening of leaves was during the advanced stages of pear rust disease. But, your trees don't show any signs of that.

    Let me see if I can duplicate the problem by doing an experiment on my trees.

    Before that, I will need some details:

    What brand of washing up liquid did you use and in what concentration?
    Was the spray bottle cleaned out before filling?
    Was the soil dry, moist, or wet when the spray was applied?
    Over what span of time did the blackening occur?


    Wouldn’t want you to get the same problem. But if you want to have a go. Original spray bottle had tap water. Mixed approx 25% fairy washing up liquid (red bottle) in water. It was during a dry spell approx 10 days ago. Noticed blackening a couple of days later. I’ll post some more pics and try and get the same part of tree to see if things have progressed 
  • IgrowfromseedIgrowfromseed Posts: 284
    Updated pics from today. The brown areas are becoming dry and crumbly
  • pinutpinut Posts: 194
    I can guess what the problem was. A 25% concentration by volume is much too strong. 

    Fairy Liquid contains surfactants which probably damaged the leaf cell walls and reacted with the green chlorophyll pigmentation inside.

    A concentration of 15ml (approx 1 tablespoon) Fairy Liquid to 1000ml of water (~1.5% concentration) would be more than adequate.

    Spraying with washing up liquid solution is not meant to be a one-shot deal. You are supposed to repeat the spraying once a day until all of the aphids are dead.


    In any case, I proceeded with the experiment using a tree that I grafted in February.



    I suspect that weather conditions/temperatures are a pertinent factor but I guess we will just have to wait and see.


  • IgrowfromseedIgrowfromseed Posts: 284
    pinut said:
    I can guess what the problem was. A 25% concentration by volume is much too strong. 

    Fairy Liquid contains surfactants which probably damaged the leaf cell walls and reacted with the green chlorophyll pigmentation inside.

    A concentration of 15ml (approx 1 tablespoon) Fairy Liquid to 1000ml of water (~1.5% concentration) would be more than adequate.

    Spraying with washing up liquid solution is not meant to be a one-shot deal. You are supposed to repeat the spraying once a day until all of the aphids are dead.


    In any case, I proceeded with the experiment using a tree that I grafted in February.



    I suspect that weather conditions/temperatures are a pertinent factor but I guess we will just have to wait and see.


    Yes 25% was way too strong. Not sure why I put so much in? Fortunately didn’t need repeat spraying as all aphids were gone. That saved the tree from further damage. Thank you for your interest 
  • pinutpinut Posts: 194
    Pictures taken today:





    The results are entirely as expected.

    Within 24hrs of spraying, the under side of the leaves exhibited brown pepper speck marks but the top side was unchanged.

    Within 48hrs, discolouration manifested on the top side. The leaf edges also started curling.

    The soil mix was still moist to the touch when the pictures were taken.
Sign In or Register to comment.