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Powdery Mildew - The main fungal disease of hydroponics · Hydroponics Daily

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  Hello and welcome back to Hydroponics Daily, the podcast all about soilless cultivation.
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  Today we're talking about powdery mildew and that's a subject I think I should
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  have covered already in the podcast because it's a fairly big common problem
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  in hydroponics, both grow room-based hydroponics and greenhouse-based hydroponics.
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  It's probably the most common fungal disease, well I know it is,
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  it's the most common fungal disease.
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  Now lots of plants get powdery mildew. Every plant apart from conifers.
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  Conifers are immune to powdery mildew. They get other diseases.
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  They get a lot of things like rusts and rots, but they are resistant to powdery mildew.
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  Every other plant, every other crop will be getting powdery mildew.
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  And it's called the same name, but it's actually lots of different species of fungi.
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  And the problem is they all look the same, so they're all given the same name.
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  Most of the ones that are on edible crops belong to the genus Blumeria,
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  so the scientific name is Blumeria graminis for those that affect all the grass
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  species and other species of Blumeria.
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  It's got the same name as the mildew that grows in your house when you've got a soggy bathroom,
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  very moist conditions, however it's completely unrelated to any molds that you
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  might call mildews in home and that can cause some problems because we have.
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  Biofungicides at Eutrema that work to control mildew on crops and then people
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  say oh it didn't work in my bathroom it's like well you're not going to activate
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  plant defense mechanisms in your bathroom so mildew is a term that's just used
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  for any sort of mold whether that's black mold or white mold.
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  And in plants, as I say, everything that gives a powdery appearance on the leaves
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  is called powdery mildew and everything that gives sort of like a downy,
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  a hairy type growth is called downy mildew.
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  So the downy mildews are not related to powdery mildews, completely unrelated,
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  as related as you are to an octopus.
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  So completely unrelated, they just look similar to the human eye.
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  When you actually get on a microscopic level and a genetic level completely
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  different and powdery mildews are far more common and they are common when you've
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  got really high humidity in the air, high temperatures and dry soils.
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  So a lot of hydroponic growers like to keep their soils on the dry side and
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  if you've got a high temperature in the summer this is where you're going to
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  really struggle with powdery mildew.
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  The good news is that because they're completely unrelated and.
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  The different types of powdery mildew on the different crops,
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  you can't get cross-contamination.
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  So if you've got powdery mildew on your tomato plants and your tomato plants
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  share a grow room or a greenhouse with cucumbers, you're not going to get cross-contamination
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  because they can only infect the plant that they've evolved to infect.
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  So that's not a problem. However, the same conditions will stimulate the growth.
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  So wet air, humid air, and dry soils, high temperatures.
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  High nitrogen levels will also stimulate powdery mildew
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  and a crowded grow room where you've got those conditions
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  of high humidity is going to exacerbate that
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  with having a crowded grow room so be careful
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  of that just when you think about cramming more plants in having under canopy
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  lighting powdery mildew will be your biggest problem so as i say it's often
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  it's white growth on your leaves if it starts to turn black that means it's
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  sporulating producing microscopic spores and then you're in a world of pain
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  because you're going to get even more powdery mildew.
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  Your whole installation will be covered in spores and so you really want to
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  control it way way way before you get to the sporylation phase.
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  It's a biotrophic fungus and by that means it feeds off the plants and it doesn't kill the cells.
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  It just sucks the energy out of them, the life out of them.
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  That contrasts with a necrotrophic fungus
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  which just eats the plant as you go along so something like fusarium
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  is a is a is a necrotrophic fungi but a biotrophic one it goes into stealth
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  mode it's like a parasite in the cells and that's important because if you do
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  apply things like chitosan which is a biofungicide it activates the plant defenses
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  and makes them turn on and recognise the plants.
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  And so the powdery mildew, to get a bit nerdy, actually turns off the plant
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  defences. It means it can't sense it.
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  And the plants are normally trying to look out for chitin which is what
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  all fungal cell walls are made of and all pests are made
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  of the fungus goes in turns those defenses off and that's
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  how it becomes biotrophic and leads to an infection the plant
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  just doesn't know it's there so if you go on with something like chitosan a
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  biofungicide and spray it on suddenly the plant wakes up and realizes oh
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  shit i'm under attack okay so that's one
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  one good way of of looking at powdery mildew
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  ways of controlling powdery mildew obviously quarantining
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  any new plant material that comes in that's really important if you're
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  growing a plant that's not common in
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  your area because you're only going to
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  get it really it comes in on the air through
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  it'll go through any inlet filter so you can't really keep the
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  spores out it'll come in through vents it will
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  come but if you say you've got a plant
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  that only grows no one grows it near you and it only normally
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  grows in japan then it's going to come in on the plant material so
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  you've got to be really careful quarantining it or even seeds you
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  can you've got to make sure you sterilize them as we know at
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  utreema we deal with a lot of seed companies and they have powdery mildew issues
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  you know there's not a grower out there there's no powdery mildew issues they
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  can try and reduce those the incidence of powdery mildew by growing it in places
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  where there's a lot drier air warmer conditions in the winter.
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  But they still have powdery mildew.
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  Anyone who's growing a seasonal crop in tropics like Thailand,
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  they'll have powdery mildew.
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  So quarantine is essential, seed sterilisation is essential.
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  You can, there are ladybirds that actually eat powdery mildew,
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  and people have looked at this as a biocontrol.
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  I think they're native to, it might be native to the UK, but certainly native
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  to Australia, you get a lot of yellow ladybirds down there.
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  And so there's potential for biocontrol that you could release yellow ladybirds.
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  I don't think anyone does that at the moment.
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  So I've said kitesan is a biofungicide. There are conventional fungicides, however,
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  do you want to be eating fungicides and normally they
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  can't be applied 30 days until harvest and they can only be applied
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  once or twice on a crop whereas chyterzan you
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  can apply at any time you can play up to eight times i
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  think legally in the eu and the uk and you can apply it right up until harvest
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  because it's you know food grade and you don't need to get your people out of
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  your greenhouse while you're while you're spraying it so that's really good
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  for commercial situations where you don't want to stop production for 30 days
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  and you don't want to take people out the greenhouse while you're spraying.
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  So have a look at chitosan. Chitosan is spelled C-H-I-T-O-S-A-N.
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  Some people call it chitosan. I've heard it called chitosan,
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  but it's called chitosan.
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  You might also want to look at resistant varieties.
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  Some plants, they breed for resistance to powdery mildew.
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  So things like arable crops and also pea crops,
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  whereas in other medicinal plants and things like this, they
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  don't breed for powdery mildew resistance it's not
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  a big one in hops it's more like verticillium fusarium rules
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  things like this where they're going to breed out viruses they're
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  trying to breed those out a great example of breeding
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  for successful preventing powdery mildew is
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  sweet peas so sweet peas normally get really do get a lot of powdery mildew
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  and it's found that wild peas don't get powdery mildew so they bred in the genes
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  for just conventional breeding by crossing them with the wild peas and then
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  crossing the progeny of that cross with sweet peas again,
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  they sort of got back to a sweet pea variety.
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  Crucially, still maintaining the powdery mildew resistance they got from the
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  wild pea on the initial cross.
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  So that's really interesting that you, you know, if you want to go out there
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  and look for powdery mildew resistance in your plant species you work with,
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  maybe you could breed a powdery mildew resistant variety or strain or cultivar.
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  However, certainly arable farmers, they'll know that disease resistance is not
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  a static thing. and some varieties that were once considered fully resistant
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  now get the disease commonly and things like that.
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  So that's something to consider. Don't look at old literature and say,
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  oh, that one's resistant to it because it might not be resistant.
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  Powdery mildew is an interesting fungus. You'll often see claims from vertical
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  farmers that vertical farms say that one of the reasons vertical farming is
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  great is because there's no pest or disease in the grow room in these vertical farms.
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  And I can believe there's no pests but i
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  can't believe there's no powdery mildew you think about all the stacks and
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  stacks of of plants growing in luscious nutrient
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  rich water fertigation solution
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  and and all that requirements who
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  have air being sucked in unless they've got extremely good
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  filters i would imagine powdery mildew will
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  rear its head and will need to be controlled just like
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  any other growing environments so powdery mildew
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  i think is probably more prevalent in vertical
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  farms than people are letting on it's say it's
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  the number one problem in in grow rooms certainly because
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  you in the summer it's going to get really hot and humid
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  when you look at ways to control
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  powdery mildew you will see reports of lots
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  of different homemade solutions working so
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  people say you know milk spraying milk onto your plants helps
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  control powdery mildew what else like let's
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  have a look i made a list when i was writing my
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  book and so here we go so potential standard kitchen spice rack ingredients
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  that people have done studies on ginger turmeric asafadikta that's an indian
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  spice isn't it peppermint mustard and they've all been found to show effects
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  against powdery mildew garlic,
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  field horsetail, Japanese knotweed, oilseed rape,
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  ginger, sweet flag, even some poisonous plants.
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  And the key thing to remember here is that in these studies,
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  very rarely did they spray on a water control treatment onto the control plants.
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  Because in science, when you're doing a treatment to see if it has an effect,
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  you spray water onto the control plants and then you have your extract on your
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  other plants whereas these were just assuming that water was not going to control
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  powdery mildew and in reality spraying anything onto your crop helps control
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  powdery mildew and that's because.
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  The spores of powdery mildew germinate instantaneously as soon as they're in water.
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  And so they think they're in the plant. And so they produce their long germination
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  tube and try and get themselves into a stomata.
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  And if you're spraying water on them, they're washing off and they're germinating.
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  So spraying anything controls powdery mildew. And that's why they've got all
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  these reports of all these different plants and all these different
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  spices and food ingredients that potentially could control
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  powdery mildew because people haven't realized they should have been
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  spraying the water on the control to have a fair comparison when
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  you do that the results are a lot less infrequent that
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  you get a good control of powdery mildew you will
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  see some products that are based on copper for controlling
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  powdery mildew and especially downy mildew as we said is
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  completely unrelated don't be spraying copper based products like
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  bordeaux mixture they are extremely toxic
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  to you the soil and if
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  you're eating crops that contain copper it's not good for you it's
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  a heavy metal it's residual so and
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  it and it kills the soil biology so don't spray copper even if
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  you think it's more natural than spraying a fungicide i would rather
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  i'd rather eat crops that have been sprayed with fungicide than
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  sprayed with copper but preferentially i'd spray them with
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  chitosan as a as a biofungicide so that's
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  been hydroponics daily for today a long overdue episode about
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  powdery mildew probably do a follow-up because i've probably missed loads
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  about powdery mildew it's a massive subject and there's
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  loads to consider so until tomorrow if you found this interesting if you know
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  somebody's suffering from powdery mildew then share it with them if somebody
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  shared this episode with you you owe them a pint get down the pub and and get
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  that person a pint it's hot weather they could do with it okay thank you very
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  much for listening till tomorrow goodbye.