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What does 'senescence', 'necrosis', 'abscission', and 'chlorosis' mean? · Hydroponics Daily

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  Hi, welcome back to Hydroponics Daily with me, Dr. Russell Sharp.
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  Today, I want to talk about four different words and their meaning.
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  They're four words that are very important when you come to diagnosing a problem
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  with your crop that you're growing hydroponically.
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  Okay, and they all relate to the problems that are going wrong with the leaves.
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  And And this is a term we use that means, in layman's terms,
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  the leaves are going yellow.
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  However, if they aren't going yellow, the chlorophyll is being removed.
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  And that is then allowing the other pigments, like the carotenoids, to be shown on the leaf.
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  So chlorosis means a removal of chlorophyll. So normally chlorosis is associated
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  with something that's causing chlorophyll to break down.
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  And that's most commonly a nutrient deficiency.
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  So nitrogen, the yellowing of older leaves at the bottom of the plant,
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  that's a really good sign of nitrogen deficiency.
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  If you're getting yellowing of leaves at the bottom, you might get yellowing
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  on the very young leaves, and that's most commonly.
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  An iron deficiency caused by a pH imbalance, but
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  it could be a sulfur deficiency and it
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  could be magnesium deficiency as well they're they're
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  the most common forms of chlorosis now senescence
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  is when the leaves are
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  going brown and dying off so this
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  could be a natural process where like in
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  autumn in or fall when the leaves go
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  turn brown first before they fall off that is senescence and
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  senescence can be caused by a number of things but it is
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  exacerbated by dry soil and
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  so senescence is a big problem there or if
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  you're using a very high electrical
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  conductivity in your media so you're
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  using a lot of fertilizer there's a there's one brand
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  out there that plays a lot on the
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  science and they have a very very high ec
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  and they're starting to come into the uk and we're.
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  Seeing a lot of senescence on the crop where people are not used to it
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  and they're adding additives on top of these base
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  nutrients and they're seeing senescence because of because of
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  this so it might be senescence or the leaves might
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  just go crispy and and and die off that way
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  the the next word is abscission now
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  abscission is where your leaves just fall off like that they're still green
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  so it's not like in the fall or the autumn where they go normally turn brown
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  or a different or red first or yellow abscission is just the leaves falling
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  off and that's normally due to.
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  A build up a burst of ethylene in
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  the plant there's something called the abscission zone on the
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  petiole the leaf stalk and that's the
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  cells there die off in response to ethylene and then the.
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  Leaf just falls off so most commonly this
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  will be flooding that's causing this but anything where.
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  Oxygen has in the root system has.
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  Been removed will cause abscission so
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  it could be flooding that's the most common cause it could
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  be you've used a really sugary additive and microbes
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  have consumed all of the oxygen in the
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  growing media it could be compaction and root damage
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  that have caused this wounding of the of the
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  roots that's a common cause of abscission and
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  then the final word i want to define is
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  necrosis and this is blackening
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  of the leaf tissues all the fruits and
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  this is most commonly associated with calcium deficiency
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  so if you're growing in cocoa and you're
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  you're new to hydroponics and you're using a base nutrient
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  that's bought from a garden center or home depot
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  or something like that and it doesn't have calcium in so
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  the great thing about gold leaf or liquid gold is it
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  contains calcium and it's a one part so you don't get
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  necrosis if you're growing tomatoes so a tomato
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  you get blossom end rot on the bottom of the tomato it
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  might look like a fungal disease but that black blackening of
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  the young tissue is is due
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  to calcium deficiency and more importantly the lack of
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  calcium traveling in the xylem the sap going
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  from the roots to the shoots so necrosis is called by calcium deficiency and
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  then lack of calcium because you haven't watered often enough or and the water
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  has been availability has dropped so maybe high humidity very high humidity
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  the plants can't suck the sap put out of the roots, that causes necrosis.
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  You get, in lettuce, you get blackening of the heart of the lettuce,
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  very common and very common in celery as well
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  and then you can get in plants that
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  can't be named you get necrosis on the inside
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  of the leaf so next to the midrib it
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  will go brown or black and that's the sign of necrosis due to calcium deficiency
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  so just like in humans necrosis like frost frostbite that's the example of necrosis
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  calcium deficiency normally is the cause i'm trying to think of any other causes of necrosis,
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  it might be the plants can kill off their own cells and tissues in response
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  to the attack by certain diseases.
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  So in beans, you get a disease called chocolate spot. And chocolate spot,
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  the black spots on the leaf is not caused by the fungus directly.
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  It's actually the bean plant responding to the arrival and germination of a,
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  the Botrytis, I think it's Botrytis fabiae, easy for me to say.
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  Fungus it arrives on the leaf surface the plants detect
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  it and then all the cells around them
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  die off it's a scorched earth sort of policy
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  by the plant it's evolved to just kill off all the
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  cells around that fungus so that it can't establish itself so
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  that fungus then dies so it's just like the soviets in world war ii they destroyed
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  every village and all the food and all the resources and all the fuel before
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  the germans got to a town so that they couldn't use that to then further their
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  advance into the Soviet Union.
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  Plants do exactly the same thing under certain circumstances and that's why
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  you get black spots necrosis on things like beans but it happens in other plants as well.
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  So that could be a sign of disease if you get in black spots.
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  So necrosis blackening of tissue, abscission, the dropping off,
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  senescence, browning and chlorosis yellowing.
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  Now one last point is that there is a hormone in plants called ABA.
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  And ABA is the stress hormone that travels from the roots to the shoots under
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  dry conditions or stressful conditions.
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  And it was initially termed abscissic acid, hence the name ABA.
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  But it's actually not the hormone responsible for abscission.
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  It's ethylene is responsible. And actually, ABA is probably acting against,
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  counter to ethylene in many situations. ABA promotes root growth under drought conditions.
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  It's antagonistic to ethylene in a lot of situations.
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  So don't think that ABA, even though the name derives from abscisic acid,
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  a lot of plant scientists now don't like using the term abscisic acid because
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  it's not beneficial to use it.
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  It's confusing. so abscission is is is is that so um it's dropping of leaves
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  and it's normally due to ethylene right that's me rambling enough hydroponics
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  daily for today is just clarifying a lot of,
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  scientific terms you might see in the literature when you're looking at pest
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  and disease and nutrient deficiencies until tomorrow thank you very much for
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  listening and share if you found this useful.