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Mildew

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richardh View Drop Down
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Joined: 27 Jan 2007
Location: England
Posts: 38
  Quote richardh Quote  Post ReplyReply Direct Link To This Post Topic: Mildew
    Posted: 07 Jun 2007 at 6:18pm
I have several texensis,crispa and addisonii species all of which are just budding up nicely.Every year I try a different regime,dry or wet,hot or cold ,pot or garden,outside or in shaded greenhouse to try and avoid the dreaded mildew.I have sprayed other years with Systhane,which I use for roses,but my stock is now exhausted and I believe it is not available now.Any recommendations please?
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Paul View Drop Down
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Joined: 19 Dec 2006
Posts: 42
  Quote Paul Quote  Post ReplyReply Direct Link To This Post Posted: 07 Jun 2007 at 9:32pm
Powdery mildew development is favoured by periods of hot weather coupled with high humidity but not by rainy weather. This combination of conditions is usually met during the summer months during dry periods when the night humidity is high.

Keeping the plants in a place where there is a good air circualion and not in the shade will help. Avoid watering in the evening to discourage the build-up of humidity.

If you start spraying early, before any symptoms occur, you should be able to keep the disease under control. If you have problems then keep the spray intervals short. Once symptoms are present, it is much more difficult to control the disease. In this situation you need to apply the first 2-3 sprays at a 7 day interval. Any symptoms that are already present will remain but sporulation will be stopped and new growth will be protected.

The number of fungicides registered for amateur use in the UK are limited. The most effective ones belong to the triazole group of fungicides which includes Systhane (active ingredient myclobutanil). Other active ingredients belonging to this group available for amateur use are penconazole and propiconazole.

If you go to https://secure.pesticides.gov.uk/pestreg/ProdSearch.asp and select 'fungicide' under Field of Use and 'Amateur' below it, you will get a list of products which are registered in the UK with the active ingredient given in the right hand column.
Paul
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keith View Drop Down
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  Quote keith Quote  Post ReplyReply Direct Link To This Post Posted: 07 Jun 2007 at 9:47pm
Unfortunately they are prone to mildew, and don't I know it!  Ventilation is crucial, as is not allowing them to dry out.  I spray on a regular basis - about once every 3 - 4 weeks from about April onwards, and this does help, but I do rotate between fungicides, to try to avoid any resistance being built up.  As you are aware yourself, the shrinking list of treatments available, especially to the amateur, does make life more complicated, but you just have to try that little bit harder.  Mildew did try to break out in my second greenhouse about 3 weeks ago, but I sprayed as soon as I noticed the first indications, and currently it seems to be at bay, but watch this space, that may well change!  As I grow the majority of the species and just about all the hybrids with viornae genes in them, I am only too aware of mildew, and although I know that you must have many more plants than me, in your particular situation, I have around a thousand myself of which over 350 are officially already in my National collection, with a heck of a lot more 'pending', that is over two thirds of the plants I grow have at least 50 percent subgenus viorna in them, so unless I sprayed regularly, and kept a careful eye on things it could look as if it were perpetual snow down here.  Do persevere, they are worth it.  Incidentally, of the three species you have mentioned, I would only normally expect problems with c. texensis, as c. crispa and c. addisonii are not normally affected by mildew (that's taking a chance, saying that!).  I find that c. viorna itself is more likely to get it, particularly on young plants, and even then, only very rarely outside.  I do get spots on the leaves of various plants, presumably where mildew has attempted to start, but usually the spraying keeps away the worst outbreaks.  My 'Jackmanii Superba' tends to suffer more, even though it is outside and in the ground. Perhaps surrounding plants are robbing it of moisture more seriously than I would have thought!
keith
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