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Downy Mildew in Hydroponics · Hydroponics Daily

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  Hello there, welcome back to Hydroponics Daily.
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  I'm Dr. Russell Sharp and today we're focusing on one of the more stealthy threats
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  to hydroponic growers, downy mildew.
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  In some regions downy mildew is not an issue in certain crops and in other regions
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  it's the major issue causing complete loss of your crop.
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  So it's fairly common but often misunderstood and when it hits,
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  it hits hard particularly in leafy greens herbs
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  tomatoes and hemp and
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  legal cannabis but what exactly is downy mildew how do you spot it and what
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  steps can you do to protect your crop and treat them when you've got it so let's
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  break it all down so what is downy mildew now mildew when we think of mildew
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  we're normally talking about powdery mildew which is a fungus that attacks the plants.
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  And it's a very common disease.
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  However, downy mildew is called mildew because of the growths on the leaf,
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  but it's not actually a fungus.
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  It's what we call an umicete, or a water mould, and that's because it doesn't
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  have any chitin in its cell wall. It's got cellulose.
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  It's closely related to algae, even though it doesn't photosynthesise. It's a parasite.
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  It thrives in cool, humid environments, especially in the Mediterranean,
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  in the winter and that's when in the Mediterranean regions
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  they tend to grow their greenhouse crops in the
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  winter anyway so that's where it really does
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  thrive in those sorts of conditions so and you
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  know when you've got hydroponics you're trying to keep them cool and there's a
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  lot of water around so you can get downy mildew
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  now downy mildew is different to
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  powdery mildew which powdery mildew forms like
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  white fluffy clouds on the top of
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  your leaves whereas downy mildew forms yellow
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  spots on the top of your leaf and then if you turn the
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  the underside of the leaf up so you can see
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  it they're grayish purplish fuzz on the
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  underside of the leaf now that's for legal cannabis in
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  other crops it will be a different symptoms so check
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  that for your particular crop dynum mildew often
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  targets lettuce spinach basil cucumbers as we
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  say legal cannabis they're all the main ones early signs
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  yellowing between the leaf veins so like the spots don't
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  go between the veins curling or drooping of new growth
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  and so your plant does look really sick unlike
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  powdery mildew it will start to you know look like
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  it's having in a real bad way and then that fuzzy dusting or looking mold on
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  the underside of the leaf and that's where it's trying to sporulate it's trying.
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  To produce more spores actually it can produce zoo spores which are swimming
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  spores so they can swim through the the hydroponic solution as well so.
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  You need to look out for downy mildew. So it spreads into high humidity in enclosed
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  environments, especially in dense plant spacings, because you're going to increase
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  humidity and also increase the chance that the plants can move it between them.
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  And it can, in recirculatory systems, because you've got these zoo spores,
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  it can spread quickly from plant to plant if it's not filtered out or killed
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  by a UV filter or something like that.
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  So they love moist and airflow irregularities, foggers
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  leaky filters condensation and cold pipes
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  dropping down onto the foliage if
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  you're growing in a polytunnel the condensation that appears in the in the
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  in the in the morning if you whack the
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  polytunnel and that all drops down on your plants that's the
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  perfect conditions for the spread of downy mildew
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  so how do you prevention beats cure when
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  it comes to any sort of disease and certainly
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  plant diseases even human diseases doesn't it you know you
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  don't be trying to cure yourself of a disease if you can avoid
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  it and control humidity that's the main one keep your
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  relative humidity between 50 and 70 and avoid overnight spikes
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  you might think you've got your humidity dialed in
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  but unless you've got a data logger you can't really say what's happening at
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  night as soon as those lights go off bang your humidity can raise raise
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  dramatically use dehumidifiers if you need to or fans
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  anything you can use to modify humidity reduce
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  it in your grow room sanitizing services between
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  crops clean your trays your walls your tools they can
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  survive in nutrient film residues for a long time
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  and then downy mildew is a big problem in field grown crops where there's no
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  crop rotation and that's one of the big advantages of hydroponics especially
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  down in spain where you just you know if you've only got three greenhouse crops
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  then the spores are going to survive between them monitor your plant densities give your plants room.
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  As I say, you know, a lot of people are pushing now into canopy,
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  under canopy lighting, get more plants into agrarian wealth.
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  If you get downy mildew, you'll regret it.
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  And potentially look for resistant varieties. There are lots of varieties of
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  lettuce, basil, and cucumber that have improved resistance.
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  And, but even if they do, it can still be, you know, sorry, if it proves to
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  be a persistent issue to switch to a resistant variety, there might not be a
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  resistant variety for your crop.
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  So if it's infected what do you do you can
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  isolate the infected plants immediately if that's
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  not possible remove any infected tissues don't compost
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  them and put them back onto your plants sanitize your water use a uv sterilizer
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  or hydrogen peroxide you could apply something like lime sulfur as well as a
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  as a sterilizing agent but that smells there are biological control methods
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  bacillus subtilis there are a number of products out there depending on your jurisdiction,
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  where are you based, whether you can get hold of these and whether they're legal
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  to use, whether they're a registered pesticide, fungicide, even though it's not truly a fungus,
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  anything that attacks downy mildew will be classed as a fungicide or a bactericide.
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  Potassium bicarbonate sprays some people have used.
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  At Utrema, we sell a lot of potassium bicarbonate for control of chocolate spots on beans.
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  But apparently here you can use it for controlling downy mildew. So that would be good.
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  Remember, most chemical fungicides, though, are not suitable for hydroponic
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  systems or even legal cannabis. So verify with your crop type and your local regulations.
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  Something like potassium bicarbonate, though, is food safe. So you could probably
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  use that. And also, any biofungicide, you could try, see if it works.
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  So that's the the basics as
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  i say yellow spots between the leaves is the is
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  the between sorry between the veins on the upper
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  side of the leaves is is the classic symptom could be
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  confused with a nutrient deficiency and intervenal
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  intervenal chlorosis so but it's
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  going to be much more patchy than that it's going to be much more localized in
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  splotches and then just check the underside with a
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  magnifying glass and you'll see the sporulation the
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  growth out of the stomach so that will be the difference between
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  that and a nutrient deficiency as i
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  say it's a a foliar disease so
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  it's only affecting the foliage really it's a massive problem
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  in grapes and there are a number of resistant varieties
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  and you will see people talk about using copper and bordeaux mixture to control
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  it however i would strongly strongly advise not to because copper is a persistent
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  heavy metal that is poisonous to humans and poisonous to soil biology and any
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  sort of biology you want to put into your crop.
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  So unless you want to suffer from health effects, don't be spraying copper.
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  And unless you want the people who are consuming the food to get health effects,
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  then don't be applying copper.
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  Both root aphid and downy mildew on grapes were brought to Europe from America.
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  These are two American diseases that decimated the European.
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  Vineyards in the Victorian times, the 19th century.
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  So yeah, two very problematic issues that they've had to deal with and introduce
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  root stocks and resistant varieties for.
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  You've heard of the ornamental plant Busy Lizies or Empatian's Wallerania,
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  that's the scientific name, but Busy Lizies is the common one.
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  Some nurseries have completely given up growing those because they can't guarantee
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  that they'll be free of Empatian's Downy Mildew.
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  So for some nurseries for some
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  growers they've had to completely give up growing a
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  type of plant because of downy mildew luckily it
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  tends to be very localized downy mildew
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  and so certain regions in the world have never had things like hemp downy mildew
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  the first report in new york state of hemp downy mildew was in like 2023 and
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  i don't think there's been any reports in the uk of it so So France, Germany, Italy.
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  Poland, Russia, America, there's been a number of reports, but it's mainly one
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  for Asian and sort of warmer climates.
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  But there are lots of different types of downy mildew and they will affect different crops.
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  So if you're unlucky enough to have it, you've got my sympathy.
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  Try some of the control methods I talked about and see how you get on.
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  If you want any more advice with applying any biofungicide
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  like the ones that eutreema make then let me know if you're
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  using gold leaf at the moment it has no effect on
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  it so just a fertilizer so but you were you at
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  least your plants will be healthy if you've listened to
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  this podcast for the first time please make sure you follow it so that
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  you don't miss another episode and if you know somebody with downy mildew share
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  this episode with them and if somebody has shared this episode with you because
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  you've got downy mildew and it's of any help whatsoever you owe that person
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  a nice large shrink so get down the pub until until tomorrow i'm going to get
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  down the pub myself thank you very much for listening goodbye.