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mildew to spray or not to spray

I recently asked about a problem which turned out to be powdery mildew, I have some similar mildew on some calendulas and sweet peas, I think I remember someone saying 'don't spray', is there a problem with the sprays you can buy and will plants recover by themselves?
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  • DovefromaboveDovefromabove Central Norfolk UKPosts: 79,336
    edited September 2021
    I don't use fungicides for the reasons described in this thread

    https://forum.gardenersworld.com/discussion/1030843/fungicide-worries/p1  

    Powdery mildew amost always affects plants that have been stressed, usually by drought/lack of watering.  As with most things, prevention is so much better than the cure.

     :) 
    “I am not lost, for I know where I am. But however, where I am may be lost.” Winnie the Pooh







  • TheGreenManTheGreenMan Tyne & Wear Green Belt Posts: 1,600
    I have a verbena with mildew. It’s had it since I planted it in May. 

    It’s thriving and still has mildew. 

    I don’t spray for the reasons above. 

    Next year I will make sure it’s properly watered and hopefully that will help. 
  • B3B3 South East LondonPosts: 22,307
    Some perennials will recover if you cut them right back. The new growth will be healthy and should remain so if they're watered properly. This works for aquilegia, pulmonaria, centaurea and others whose names escape me - but not  for everything.
    In London. Keen but lazy.
  • FairygirlFairygirl west central ScotlandPosts: 47,155
    I only get it on Centaureas, but I just cut off the manky foliage, and keep them heavily watered if we've had a shortage of rain. Extremely rare, but this year has been record breaking for dry weather.  

    Sweet peas need huge amounts of water to thrive, so just keep them thoroughly soaked, and well fed. Even in wet areas, they need loads. They always get some general damage anyway, especially on lower foliage, as the season goes on, but the best solution is to have something else in front of them to hide it. In pots [where most of mine are] it tends to be worse, and I just put other pots in front. I get more damage from leaf miner than anything else. 
    It's a place where beautiful isn't enough of a word....


  • Give dilute sour milk a try. I don't normally go in or these 'old wives' remedies but I had mildew on my Asters last year and spraying on this concoction actually worked  .. much to my amazement.
  • LoxleyLoxley NottinghamPosts: 4,633
    I was reading about that the other day, Chris. 

    More than 50 years ago, researchers in Canada discovered that milk sprays could help prevent powdery mildew on tomato and barley. Then the age of fungicides began, with no further published research on the milk cure until 1999. Since then, numerous small studies from around the world have validated the use of milk sprays on powdery mildew on a wide range of plants. Most recently, a spray made of 40% milk and 60% water was as effective as chemical fungicides in managing powdery mildew of pumpkins and cucumbers grown in mildew-prone Connecticut. In Australia, milk sprays have proven to be as effective as sulphur and synthetic chemicals in preventing powdery mildew on grapes. In New Zealand, milk did a top-rate job of suppressing powdery mildew in apples.

    Using Milk to Prevent Powdery Mildew (growveg.co.uk)

  • I never used sour milk,I used 50% each milk and water, for the sweet peas and courgettes,it did help
  • BobTheGardenerBobTheGardener Leicestershire, UKPosts: 11,337
    I used neem oil dissolved in water with some horticultural soap on some squashes either last year or the year before, and it did seem to slow Powdery Mildew down noticeably.
    I suspect the neem oil and the fat in the milk create a thin protective layer on the surface of the leaves, which may reduce the chances of the spores taking hold (if it does indeed work, of course - I only have that one observation.)
    A trowel in the hand is worth a thousand lost under a bush.
  • B3B3 South East LondonPosts: 22,307
    One of the reasons I never grow sweet peas is the mildewy bottoms.😲
    In London. Keen but lazy.
  • msqingxiaomsqingxiao North LondonPosts: 343
    I've made some spray using this recipe. Sprayed my delphinium with it, seems to have worked to a certain extent. 

    Another option for treating powdery mildew is by making your own organic treatment. Combine two to three drops of dish soap with ½ tablespoon of baking soda and ½ gallon (about 2 L.) of water. This will change the pH and prevent the mildew from forming or spreading. Mist leaves with the solution.

    Read more at Gardening Know How: Powdery Substance On Hydrangeas: Powdery Mildew Hydrangea Treatment https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/hydrangea-powdery-mildew.htm

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