Light radiation falls off at an inverse square, and I'm assuming and
orchard like mine, a fruiting wall that would only be about a meter in
thickness. Because the light would be traveling through the orchard, and
the trees out of leaf, I'm guessing the shadows would be covered. Supposing
the UV required the lamps to be a maximum of four feet from the target,
then anything 8 feet away would only receive 1/4 the exposure. Any humans
40 or more feet away would only receive a minute amount of radiation,
probably less than a summer day at the beach. I'm mainly interested in the
ice nucleating bacteria portion anyway, and these bacteria are in dew, a
clear liquid. 100% control is not necessary or practical. Tractor accidents
on farms and orchards kill thousands. Trucks hauling apples kill. The risks
and rewards from UV would need to be researched.

On Tue, Apr 19, 2016 at 4:36 PM, David A. Rosenberger <>

> UV light does not penetrate surfaces, so it could only kill what is on the
> surface and only what receives the required UV dosage.   Any bacterial in
> shadows created by limbs, leaves, branches, or flower parts would remain
> untreated, and in the case of fire blight, the rapid multiplication of the
> cells that escape would probably negate the value of the treatment pretty
> quickly.   I’m not an expert on UV, but I don’t see how it could be made
> practical in an orchard.  UV works best on clear liquids (as water or thin
> layers of apple juice going by UV treatment lamps) or on flat surfaces
> where shadowing is not an issue.
> Also, from the Wikipedia article about UV-C, which is generally the most
> effective for killing microbes:  "For human beings, skin exposure to
> germicidal wavelengths of UV light can produce rapid sunburn and skin
> cancer <>. Exposure of the eyes
> to this UV radiation can produce extremely painful inflammation of the
> cornea <> and temporary or permanent 
> vision
> impairment <>, up to and
> including blindness <> in some
> cases. UV can damage the retina <> of
> the eye."
> ********************************************
> Dave Rosenberger, Plant Pathologist,
> Hudson Valley Lab, P.O. Box 727, Highland, NY 12528
>     Cell:     845-594-3060
> ********************************************
> On Apr 19, 2016, at 4:55 PM, Hugh Thomas <> wrote:
> A couple of ideas for you PhD/research types. How about using UV light to
> kill frost nucleating bacteria, or UV to kill the fire blight bacteria?  A
> light bank could be towed behind a tractor and the trees could be
> irradiated by UV light.
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