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Cornmeal/Polenta and Rose Black Spot

K67K67 Posts: 2,507
Reading the other day that a handful of cornmeal round your roses, worked in and watered as new leaves appear and repeated monthly is supposed to keep a rose clear.
Has anyone tried this before I add it to my shopping order?

Cornflour/cornmeal contains a fungus called Trichoderma which destroys the fungus that causes black spot and can also be used to clear algae from ponds according to the article.



  • B3B3 Posts: 25,280
    Sounds strange to me and an attraction to whatever fancies eating it..
    In London. Keen but lazy.
  • K67K67 Posts: 2,507


    The advice given was to spread a handful round the base of a rose bush in spring as the buds start to appear. Work it into the soil, water in and mulch so maybe that would prevent it being eaten

  • B3B3 Posts: 25,280
    Maybe. It still sounds weird but weird sometimes works. Doesn't sound like likely to do any harm but I'm not up for it😊
    In London. Keen but lazy.
  • K67K67 Posts: 2,507
    @B3 😔
    And I was hoping to recruit a guinea pig seeing as I have just bought a bottle of  Rose Clear to use!
  • B3B3 Posts: 25,280
    In London. Keen but lazy.
  • tui34tui34 Posts: 2,868
    edited March 2021
    My roses, like my vines get a blast dusting of sulphur powder for odium.  Bit early still.

    @K67  I like polenta on my plate:  after cooking, cut into wedges and fry oil  tilgolden.  Serve with tomato puree.

    I would imagine digging it into the ground would attract more mice!! 
    A good hoeing is worth two waterings.

  • NollieNollie Posts: 7,061
    Cornflour + clay soil + water. Hmm, sounds like the recipe from hell from a witless masterchef contestant. Or the great pottery throw-down. Maybe you could build walls from it?

    Unfortunately those naughty black spot spores don’t lie obediently on the ground, they whizz around in the air and crash land on the foliage, so you do need to treat the leaves as well as the base. Maybe not with cornflour tho 😊 
    Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
  • Does it matter if the cornmeal is course or fine? Willing to try anything to keep my roses free of black spot,it has been bad this year.
  • MarlorenaMarlorena Posts: 7,938
    Please, don't bother... tried it, doesn't make any difference..   waste of a good product.. save it for topping cakes or summat..
    East Anglia, England
  • JessicaSJessicaS Posts: 771
    edited October 2021
    @K67 If it helps, stuff Ive tried that does work and has really got my spottiest under control this year; blast it with fungus clear to treat the infection, removing any infected leaves and binning them (the sprays same brand as rose clear but not the combi insect/fungus one as can be bad for bees), keep base of rose clear of any dead foliedge etc, blast with sulphur rose, mulch with compost/manure or similar (not bark chips, they seen to harbour disease more) and feed the rose well which helps it fight off disease. Keep watered too. 

    Edit to add; Salvias combination planting with roses is supposed to help as they naturally contain some sulphur. Will see if I can find the article. Its a nice combo anyway!
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