See:
That’s interesting. I have a small indoor garden under lights during the winter to start seedlings. I, too, also use deluxe white mercury lamps and, for the most part, 24 hour lighting. I do turn the lights off every now and then for a night cycle but not often. I’ve never seen PM inside on any of my seedlings (no chemicals are sprayed while they are inside either). The flip side is that some plants object to 24 hour lighting and it will eventually kill them… so if you grow other plants besides roses…
Al I can say is that I always run my lights 24 hr and I had a plague of PM on a range of seedlings last winter, particularly the OP seeds of a Carefree Beauty x General Jac cross. Decreasing sporulation by 1/2 isn’t enough to keep the disease from spreading plenty.
I think part of it might be the amount of light energy the seedlings receive. Also I’ve noticed that when using six fluorescent tubes or more (6 x 40 watts= 240 watts) there is an inhibitory affect, I presume due to the emission of electromagnetic radiation due to the long arc tube length. That’s why I prefer HID lighting (with short arc tubes). I think to make the experiment fair then the amount of kilowatt-hours received should be equal regardless of light cycle.
so say I use 200 watts for the 24 hour cycle, what 4.8 kw-h. so for the 20 hour cycle, 240 watts worth of lights should be used…etc.
It looks more like an effect of ultraviolet light to me.
Jon, you are certainly right that a good test would be to give a total dose per day cut into different level x time segments. But it might be hard to pack in more than a 2-fold difference of tubes/ sq ft. Another consideration is how the lamp heat affects humidity required for fungal growth.
Don is also likely right regarding the impact of UV, although pigmented fungi are pretty resistant to UV. Your typical fluorescent does put out some UV even though it is supposed to convert it all the fluorescence over a broader wavelentgh range. Just look at how colors of posters and such fade in hallways under fluorescent lighting. It actually seems worse than the equivalent daylight exposure to me.
Halogen lamps also put out significant UV and a lot of heat.
You can use soft glass (window glass) to block the UV of certain wavelengths. Different plastics have different cutoffs too and can be used for comparison. This would make great science fair projects for several H.S. kids if the PM could be grown on petri dishes in a defined medium. What you’d end up with is a conclusion whether the effect in roses has to do with the rose or the fungus.
Perhaps the science experiment should use LEDs.
I’ve been looking at the new grow panels made of red and blue LEDs too Henry. I’ve been looking at them for my planted aquariums as they give off very little heat, last a very long time and are so much cheaper to run. This is like the one I’ve been looking at:
Have you all seen the 100 watt packaged LED panels on ebay?
They’re pricey but I would love to play with them (there’s even a blue one!).
LEDs would be a good choice to get completely free of UV.But watch the wattage. The panel you show is only 15 W, but the area covered is not described. To be fair to the fungus you need to match the total photon flux per area somehow. The LED combo ought to be very photosynthetically efficient, missing the green entirely which is good, but I’ve not seen actual data on this one compared to other light sources. The 15 W might well equal a 40 W fluorescent new and beat it old. Your best comparison probably would be to grow something easy like sunflowers and determine their mass doubling times. I grow them hydroponically all the time in 1/2 strength Hoagland’s. Start them in vermiculite and transplant to bottles of nutrient. Put several identical sized seedlings under each kind of lighting and compare daily weight gain. Doubling of fresh weight takes only a few days in a warm (25 C) place with around 1 40 W tube per sq ft table area. Growth is exponential from 1-3 wk or perhaps more if nutrients are constantly renewed. Bottle volume limits roots which constrains plants. But you can get an idea of how light is limiting by a comparison, cheaply.