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It seems that only two systemic fungicide are still on the UK market sold for rose black spots being Triticonazole (UK brand name: Fungus Clear Ultra - Scotts Company) and Tebuconazole (UK brand name: Bayer Garden Concentrated Fungus Fighter)

Can anyone point me in the direction of any research that shows how there effectiveness compares with each other?

(At present I try to use both in year and need to spray my rose hedge every few weeks to keep it clear of black spot.)

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Neither product is massively effective, simply providing some control of the problem, and neither one is any better than the other, as far as I can tell in use. The one I usually recommend for roses is Roseclear Ultra, which is a combined preparation of an insecticide and a fungal treatment (triticonazole), so it deals with aphid infestation too. Can only be applied 4 times in a year, and should not be used while the bees are still working, if the flowers are open.

https://www.lovethegarden.com/products/pests-disease/roseclear-ultra

However, given you've got a hedge, where black spot is much more likely to occur anyway, and it's difficult to get a spray to reach all parts because of the 'thicket' like nature of the growth, then I'd suggest a natural, non harmful treatment for fungal infection, particularly black spot - cow's milk. Mix one part milk to two parts water in a sprayer, and spray till run off. And you can use that mix as often as you like or as necessary, without harming anything in the environment.... link below

http://www.agardenforthehouse.com/2012/05/got-black-spot-get-milk/

  • I only use Roseclear when I have an aphid problem, as I don't wish to use more "chemicals" then I need on my 110 foot rose hedge. – Ian Ringrose Apr 25 '16 at 13:00
  • Well, the milk solution is ideal then... with the occasional insecticide separately for insect pests, if you feel you must treat for those. – Bamboo Apr 25 '16 at 13:00
  • 10% solution didn't work for my mildew problem. Maybe next year I'll try 30-100% as per the comments in your link. – Graham Chiu Apr 25 '16 at 20:01
  • @GrahamChiu - supposed to be 1 to 9 for powdery mildew, and 1 to 2 for black spot - different conditions. And the milk treatment only works on powdery mildew - downy and other forms of mildew do not respond to this treatment. – Bamboo Apr 26 '16 at 9:33
  • Bamboo told me about this ratio for milk and water and believe me it works for powdery mildew. Powdery mildew is the only fungus I know that can be controlled or 'cured' AFTER the fact the plant gets this fungus. One fungal spore can innoculate the entire plant and the best fungicide is sort of a 'raincoat'. Not allowing water to splash off the ground and onto the plant. Please send pictures of your black spot on your hedge. Sometimes it is beneficial just to relax about a few insects a few spots. Completely normal and healthy plants can usually take care of this stuff all by themselves. – stormy Apr 26 '16 at 22:06

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