greenfly
 

I know its not a garden query but what can i use on African Violets to
get rid of greenfly Thanks

greenfly
 

"Heather" wrote in message
...
I know its not a garden query but what can i use on African Violets
to
get rid of greenfly Thanks

I'd normally reply that you should spray with a mild solution of soapy
water, but methinks that African violets do not like getting their
leaves wet........

Your best bet is to crush them gently !

Jenny

greenfly
 

The message
from "JennyC" contains these words:

"Heather" wrote in message
...
I know its not a garden query but what can i use on African Violets
to
get rid of greenfly Thanks

I'd normally reply that you should spray with a mild solution of soapy
water, but methinks that African violets do not like getting their
leaves wet........

Your best bet is to crush them gently !

The greenfly, or the African violets? I've used Sybol to get rid of
greenfly and whitefly on pot plants. I don't know how African violets
would cope with it though.

--
Tony
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greenfly
 

The message
from "JennyC" contains these words:


"Heather" wrote in message
...
I know its not a garden query but what can i use on African Violets
to
get rid of greenfly Thanks

I'd normally reply that you should spray with a mild solution of soapy
water, but methinks that African violets do not like getting their
leaves wet........

Your best bet is to crush them gently !

I wash my African violets under the tap (tepid water not cold) to
rinse dust off their hairy leaves, and they don't seem to mind at all.
You can probably get rid of the greenfly after a few washes. Just let
the plants dry off out of the sun so the water drops don't make scorch
marks.

Janet.

greenfly
 

The message
from Janet Baraclough contains these words:

I wash my African violets under the tap (tepid water not cold) to
rinse dust off their hairy leaves, and they don't seem to mind at all.
You can probably get rid of the greenfly after a few washes. Just let
the plants dry off out of the sun so the water drops don't make scorch
marks.

Scorch marks due to droplets of water is an old - er - partner's tale,
Janet. You cannot concentrate the sun's rays (either direct or diffused)
with a sphere or an hemisphere.

I remember Geoffrey Smith pointing that out on GQT ages ago, and
thinking about it, he was quite correct.

--
Tony
Replace solidi with dots to reply: tony/anson snailything zetnet/co/uk

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greenfly
 

In article ,
Anthony E Anson writes:
| The message
| from Janet Baraclough contains these words:
|
| I wash my African violets under the tap (tepid water not cold) to
| rinse dust off their hairy leaves, and they don't seem to mind at all.
| You can probably get rid of the greenfly after a few washes. Just let
| the plants dry off out of the sun so the water drops don't make scorch
| marks.
|
| Scorch marks due to droplets of water is an old - er - partner's tale,
| Janet. You cannot concentrate the sun's rays (either direct or diffused)
| with a sphere or an hemisphere.
|
| I remember Geoffrey Smith pointing that out on GQT ages ago, and
| thinking about it, he was quite correct.

Eh? Oh, yes, you can! If you look at suitable museums, you will
see that globes of water were used to concentrate rushlight etc.
so that seamstresses could work in the winter.

A sphere of something with a higher refractive index than air is
a condensing lens, and water has an index of c. 4/3. Because the
focal point is not ON the sphere, actually scorching can occur
only if the droplet is held away from the surface (say, by hairs)
or the sunlight is slanting to the surface.

All good O-level physics.


Regards,
Nick Maclaren.

greenfly
 

The message
from (Nick Maclaren) contains these words:

Scorch marks due to droplets of water is an old - er - partner's tale,
| Janet. You cannot concentrate the sun's rays (either direct or diffused)
| with a sphere or an hemisphere.
|
| I remember Geoffrey Smith pointing that out on GQT ages ago, and
| thinking about it, he was quite correct.

Eh? Oh, yes, you can! If you look at suitable museums, you will
see that globes of water were used to concentrate rushlight etc.
so that seamstresses could work in the winter.

But not tangential to the surface.

A sphere of something with a higher refractive index than air is
a condensing lens, and water has an index of c. 4/3. Because the
focal point is not ON the sphere, actually scorching can occur
only if the droplet is held away from the surface (say, by hairs)
or the sunlight is slanting to the surface.

I think you'll find that the focal point of the light emanating from a
sphere of water is immaterial - the angle of incidence of the light
hitting the water/air interface is such that most of it is reflected,
not refracted, which is why dew sparkles...

All good O-level physics.

Good A-level physics too.

--
Tony
Replace solidi with dots to reply: tony/anson snailything zetnet/co/uk

http://www.users.zetnet.co.uk/hi-fi

greenfly
 

In article ,
Anthony E Anson writes:
|
| A sphere of something with a higher refractive index than air is
| a condensing lens, and water has an index of c. 4/3. Because the
| focal point is not ON the sphere, actually scorching can occur
| only if the droplet is held away from the surface (say, by hairs)
| or the sunlight is slanting to the surface.
|
| I think you'll find that the focal point of the light emanating from a
| sphere of water is immaterial - the angle of incidence of the light
| hitting the water/air interface is such that most of it is reflected,
| not refracted, which is why dew sparkles...
|
| All good O-level physics.
|
| Good A-level physics too.

Really? I would have given it poor marks even at O-level!

Yes, the majority of the light hitting a dewdrop (or globe of
water) may well be reflected, but that is not the issue. The
issue is whether the PEAK intensity is enough to cause trouble,
and that will be dominated by the rays that hit near-normally.
It doesn't matter that we are talking about a disc 0.1 mm across,
as that is still much larger than a leaf cell.

I don't know the relevant formulae, so can't do the calculations,
but have observed light being concentrated by droplets. As you
should expect, the area behind the droplet is darker than that
which is fully exposed, but the very centre can be lighter.


Regards,
Nick Maclaren.

greenfly
 

The message
from "JennyC" contains these words:

"Heather" wrote in message
...
I know its not a garden query but what can i use on African Violets
to
get rid of greenfly Thanks

I'd normally reply that you should spray with a mild solution of soapy
water, but methinks that African violets do not like getting their
leaves wet........

Your best bet is to crush them gently !

The greenfly, or the African violets? I've used Sybol to get rid of
greenfly and whitefly on pot plants. I don't know how African violets
would cope with it though.

--
Tony
Replace solidi with dots to reply: tony/anson snailything zetnet/co/uk

http://www.users.zetnet.co.uk/hi-fi

greenfly
 

The message
from "JennyC" contains these words:


"Heather" wrote in message
...
I know its not a garden query but what can i use on African Violets
to
get rid of greenfly Thanks

I'd normally reply that you should spray with a mild solution of soapy
water, but methinks that African violets do not like getting their
leaves wet........

Your best bet is to crush them gently !

I wash my African violets under the tap (tepid water not cold) to
rinse dust off their hairy leaves, and they don't seem to mind at all.
You can probably get rid of the greenfly after a few washes. Just let
the plants dry off out of the sun so the water drops don't make scorch
marks.

Janet.

greenfly
 

The message
from Janet Baraclough contains these words:

I wash my African violets under the tap (tepid water not cold) to
rinse dust off their hairy leaves, and they don't seem to mind at all.
You can probably get rid of the greenfly after a few washes. Just let
the plants dry off out of the sun so the water drops don't make scorch
marks.

Scorch marks due to droplets of water is an old - er - partner's tale,
Janet. You cannot concentrate the sun's rays (either direct or diffused)
with a sphere or an hemisphere.

I remember Geoffrey Smith pointing that out on GQT ages ago, and
thinking about it, he was quite correct.

--
Tony
Replace solidi with dots to reply: tony/anson snailything zetnet/co/uk

http://www.users.zetnet.co.uk/hi-fi

greenfly
 

In article ,
Anthony E Anson writes:
| The message
| from Janet Baraclough contains these words:
|
| I wash my African violets under the tap (tepid water not cold) to
| rinse dust off their hairy leaves, and they don't seem to mind at all.
| You can probably get rid of the greenfly after a few washes. Just let
| the plants dry off out of the sun so the water drops don't make scorch
| marks.
|
| Scorch marks due to droplets of water is an old - er - partner's tale,
| Janet. You cannot concentrate the sun's rays (either direct or diffused)
| with a sphere or an hemisphere.
|
| I remember Geoffrey Smith pointing that out on GQT ages ago, and
| thinking about it, he was quite correct.

Eh? Oh, yes, you can! If you look at suitable museums, you will
see that globes of water were used to concentrate rushlight etc.
so that seamstresses could work in the winter.

A sphere of something with a higher refractive index than air is
a condensing lens, and water has an index of c. 4/3. Because the
focal point is not ON the sphere, actually scorching can occur
only if the droplet is held away from the surface (say, by hairs)
or the sunlight is slanting to the surface.

All good O-level physics.


Regards,
Nick Maclaren.

greenfly
 

The message
from (Nick Maclaren) contains these words:

Scorch marks due to droplets of water is an old - er - partner's tale,
| Janet. You cannot concentrate the sun's rays (either direct or diffused)
| with a sphere or an hemisphere.
|
| I remember Geoffrey Smith pointing that out on GQT ages ago, and
| thinking about it, he was quite correct.

Eh? Oh, yes, you can! If you look at suitable museums, you will
see that globes of water were used to concentrate rushlight etc.
so that seamstresses could work in the winter.

But not tangential to the surface.

A sphere of something with a higher refractive index than air is
a condensing lens, and water has an index of c. 4/3. Because the
focal point is not ON the sphere, actually scorching can occur
only if the droplet is held away from the surface (say, by hairs)
or the sunlight is slanting to the surface.

I think you'll find that the focal point of the light emanating from a
sphere of water is immaterial - the angle of incidence of the light
hitting the water/air interface is such that most of it is reflected,
not refracted, which is why dew sparkles...

All good O-level physics.

Good A-level physics too.

--
Tony
Replace solidi with dots to reply: tony/anson snailything zetnet/co/uk

http://www.users.zetnet.co.uk/hi-fi

greenfly
 

In article ,
Anthony E Anson writes:
|
| A sphere of something with a higher refractive index than air is
| a condensing lens, and water has an index of c. 4/3. Because the
| focal point is not ON the sphere, actually scorching can occur
| only if the droplet is held away from the surface (say, by hairs)
| or the sunlight is slanting to the surface.
|
| I think you'll find that the focal point of the light emanating from a
| sphere of water is immaterial - the angle of incidence of the light
| hitting the water/air interface is such that most of it is reflected,
| not refracted, which is why dew sparkles...
|
| All good O-level physics.
|
| Good A-level physics too.

Really? I would have given it poor marks even at O-level!

Yes, the majority of the light hitting a dewdrop (or globe of
water) may well be reflected, but that is not the issue. The
issue is whether the PEAK intensity is enough to cause trouble,
and that will be dominated by the rays that hit near-normally.
It doesn't matter that we are talking about a disc 0.1 mm across,
as that is still much larger than a leaf cell.

I don't know the relevant formulae, so can't do the calculations,
but have observed light being concentrated by droplets. As you
should expect, the area behind the droplet is darker than that
which is fully exposed, but the very centre can be lighter.


Regards,
Nick Maclaren.

greenfly
 

The message
from (Nick Maclaren) contains these words:

| Good A-level physics too.

Really? I would have given it poor marks even at O-level!

Yes, the majority of the light hitting a dewdrop (or globe of
water) may well be reflected, but that is not the issue. The
issue is whether the PEAK intensity is enough to cause trouble,
and that will be dominated by the rays that hit near-normally.
It doesn't matter that we are talking about a disc 0.1 mm across,
as that is still much larger than a leaf cell.

It is some 45 years since I did A-level physics, but my long-term memory
is pretty good, despite my lamentable performance remembering people's
names, birthdays etc. I drew the diagram (twice, once as a check) and
the focus for the light which is admitted to the sphere is approximately
the radius of the diameter of the sphere, measured from the centre.

However, only a small proportion of the light which falls on the surface
passes through - much of it is reflected. Some of what does enter is
absorbed, some is reflected within because the angle of reflection of
light passing from water into air is such that much less light than
enters can directly exit.

Then, in the very unlikely event of any part of the leaf touching the
focus, your whole hypothesis falls over because the sun continues to
move the goalposts.

I don't know the relevant formulae, so can't do the calculations,
but have observed light being concentrated by droplets. As you
should expect, the area behind the droplet is darker than that
which is fully exposed, but the very centre can be lighter.

Angle of refraction = angle of incidence x refractive index. For my
diagram I've used your figure of 3/4 - 4/3 for refractive index, which
seems a little high to me. However, just look at it from the commonsense
angle - if it were possible to damage a plant's surface in this way
there would be evidence of it occurring in RL - er - Real Life - and
there isn't.

--
Tony
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