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#1
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greenfly
I know its not a garden query but what can i use on African Violets to
get rid of greenfly Thanks |
#2
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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 |
#3
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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 ! 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 |
#4
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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. |
#5
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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 |
#6
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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. |
#8
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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. |
#9
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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 ! 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 |
#10
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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. |
#11
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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 |
#12
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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. |
#13
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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 |
#14
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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. |
#15
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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 Replace solidi with dots to reply: tony/anson snailything zetnet/co/uk http://www.users.zetnet.co.uk/hi-fi |
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