UV burn on plants?

[Loohan]

I have a Japanese Black Mint in a pot in my 27-gallon vivarium. I put it in there despite being in too large a pot, because i didn't have much else going in the winter.
I plucked several of the top runners and stuck them in a smaller pot, and stuck it in the vivarium too. Once those get going (and some pothos i'm rooting), i'll remove the big pot. For right now, i sometimes see Rorg hanging out under the drooping runners from the big plant, so i want to leave it there since he has no other plant cover going yet.

I have a 24" Reptisun 5.0 tube only a few inches from the plant. I notice that some of the upper leaves (which are normally a dark green) have gotten discolored with yellowing and blotches.
The starts in the small pot look fine, and are at a lower altitude.

 

[Loohan]

I should admit i let the plant dry out too much a couple days ago. Maybe that's all it is. Some of the most yellow leaves are on the droopy runners, whereas some of the darker leaves are at the top.

 

[Yvonne G]

The leaves will burn if they're too close to the light. I try to off-center them just a bit.

 

[ZEROPILOT]

I also use a 5.0 Reptisun. No harmful effects. I only get leaf yellowing on plants that have been over watered.

 

[Loohan]

Hmm, well this is a mint in a plastic pot, usually immune to overwatering. After i moved it to the other side of the box, it continued to die back, with most of the leaves turning crispy. Now it is starting to grow again, but mainly in the vines nearest to the light, and they are making a bee-line for the light. I expect them to get fried soon.

 

[Loohan]

Now i had to remove the SMALL pot from the enclosure, because the new mint starts are getting fried bad. In fact the one closest to the light is completely crispy and yellow now.

This is how my enclosure looked on the 23rd:



The pot is in lower right corner. But since then, it has lost much of its green color. The leaves have that same speckled fried look now as the worst leaves in my original pic on this thread.
I wonder if the tube (reptisun 5.0) puts out too much UV? Anyway, i have a spare of the same brand, and will swap them out.

 

[leigti]

Is the plants getting too hot? My leaves I have high output bulbs in my enclosure and they only leaves turn yellow are either very close to the light or directly under the heat lamp. so as they grow I have to move them around.

 

[Tom]

5.0 bulbs put out hardly any UV at all, according to my two different Solar Meters. Even just a few inches from the bulb, I barely get any UV out of them. Even the 10.0 bulbs put out very little UV. at 10-12" I only get a UV Index of 1.1 out of new 10.0 bulbs. Winter mid day sun gives me readings of 4ish for comparison. Summer sun gets me into the 7-8 range here.

For more comparison, I have a 4-5 year old MVB that gives me readings of 7.1 from 12" and through a screen. I also have Arcadia 12% HO bulbs that give me readings of 5-6 at 18-20" away.

The 5.0 bulbs I checked barely registered 0.1 at 5-6" away.

I don't think UV burn is your issue.

 

[Loohan]

Well that's strange. The larger plant has always been on the cool end of the tote. The small pot was by the CHE, but the CHE is angled away and it is not very hot where the plant was.

I have grown this mint for 20 years. I have grown in in full summer sun in Austin, TX and AR. It does fine if kept moist. I grow it outside in indirect light in recent years, because it is easier to keep moist in the summer. It never seems to mind wet, heat, shade, or light. I have not let it dry out in the tote except maybe once in the big pot weeks ago.

So if it's such a versatile plant, and it's not heat or drought, and not UV, i am baffled. I have never noticed the leaves looking like this before.

 

[Tom]

You are not alone. Plants confound and baffle many of us. Certainly me. Perhaps the plant needs more light or more UV?

Maybe @Iochroma will have some insight? or @cdmay ?

 

[Loohan]

I doubt it. I have grown in in shadier places as well as indoors behind glass (which blocks UVB at least) no problem.
Also this shows up way to fast to be UV deficiency. People grow plants indoors without UV all the time, although it's not ideal.
I am a fairly seasoned horticulturist.
Maybe there is a wide variation in output with these tubes? How many 5.0's did you test, Tom?

 

[Tom]

I doubt it. I have grown in in shadier places as well as indoors behind glass (which blocks UVB at least) no problem.
Also this shows up way to fast to be UV deficiency. People grow plants indoors without UV all the time, although it's not ideal.
I am a fairly seasoned horticulturist.
Maybe there is a wide variation in output with these tubes? How many 5.0's did you test, Tom?

I've only tested a few, but many other testers report the same thing. It is possible your bulb is an anomaly, just doesn't seem likely. Getting another 5.0 bulb and trying that out over your plant would be less expensive than buying a UV meter. Wanna try it?

 

[TortsNTurtles]

@Tom when you have tested the 5.0 tubes was it the T5ho bulbs?

 

[Loohan]

Well, yeah, i swapped it out with my spare (which is new) an hour or so ago. But i am reluctant to put the small pot back yet. For one thing, i will probably get more damage on a delayed basis anyway, even with it out.
Maybe i will put a small pot of oregano in just to see what happens. I don't have a big choice of plants this time of year.

 

[Tom]

@Tom when you have tested the 5.0 tubes was it the T5ho bulbs?

No. Just the regular 5.0 tubes. 24" and 48".

 

[TortsNTurtles]

@Tom when you have tested the 5.0 tubes was it the T5ho bulbs?

Thanks

 

[Loohan]

5.0 bulbs put out hardly any UV at all, according to my two different Solar Meters. Even just a few inches from the bulb, I barely get any UV out of them. Even the 10.0 bulbs put out very little UV. at 10-12" I only get a UV Index of 1.1 out of new 10.0 bulbs. Winter mid day sun gives me readings of 4ish for comparison. Summer sun gets me into the 7-8 range here.

For more comparison, I have a 4-5 year old MVB that gives me readings of 7.1 from 12" and through a screen. I also have Arcadia 12% HO bulbs that give me readings of 5-6 at 18-20" away.

The 5.0 bulbs I checked barely registered 0.1 at 5-6" away.

I don't think UV burn is your issue.

Tom, what kind of meters were used? Are you familiar with this info:
http://www.uvguide.co.uk/phototherapyphosphor-tests.htm

(quote)
The lower UV wavelengths of sunlight (around and below 300nm) are much more biologically active than the higher wavelengths (up to 320nm). It is these lower wavelengths which enable vitamin D3 synthesis, and in general, the lower the wavelength of UV light, the greater the potential for damage to skin and eyes, too.

Could these lamps have a higher proportion of their UVB in these lower wavelengths, making their UV light more photobiologically active - i.e. "stronger" - than sunlight?

Broadband UVB meters, such as the Solarmeter 6.2, measure the entire UVB range (280 – 320nm) and give a readout of the total UVB irradiance in µW/cm². They cannot give any indication of what percentage of the total UVB is in the more biologically active, lower wavelengths. Therefore, a simple comparison of the readings from a broadband meter from the sun and from a lamp with "stronger" UV light could be misleading as regards the potential of the lamp to cause cell damage, photo- kerato-conjunctivitis, or, for that matter, to enable the synthesis of vitamin D3.

(end quote)

Also, Staten Island Zoo tested these bulbs:
http://blogs.thatpetplace.com/thatr...uvb-lamp-product-review-part-ii/#.VPG-cMtVK1E

 

[Tom]

I have both the Solarmeter 6.2 and the Solarmeter 6.5. Most people used to use the 6.2, but many have switched to the 6.5 because it measures the narrower band of UV that is specifically needed by our tortoises. I usually measure these bulbs with both meters. The 6.5 gives us the "UV index" measurement instead of micro watts per square cm.

 

[Loohan]

I have both the Solarmeter 6.2 and the Solarmeter 6.5. Most people used to use the 6.2, but many have switched to the 6.5 because it measures the narrower band of UV that is specifically needed by our tortoises. I usually measure these bulbs with both meters. The 6.5 gives us the "UV index" measurement instead of micro watts per square cm.

Hmm, the 6.5 is what they also used in that article i linked
http://www.uvguide.co.uk/phototherapyphosphor-tests.htm
which says they got an index of 2.3 off the Reptisun 5.0. I don't see that they specify at which distance that is, but it does say "recorded with the UV Index Meter at the distance at which the Solarmeter 6.2 reads exactly 100 µW/cm² of total UVB." My little brain is getting overloaded.
But the gist of that page is that these bulbs do put out wildly excessive amounts of UV in the narrower band of UV that is specifically needed by our tortoises. Measured with the same meter you have.
Of course the article is 8 years old and the bulbs may have been modified since.

And i do have an aluminum reflector, and my mint plants have responded as if they were getting fried.

 

[weldorNate]

Plants that get sun burnt turn white. I did it to my spider plant last summer had it in my room by the window during the winter then took it out when it got nice here for some real sunshine and put it in direct sunlight and most of the leaves all turned white. It is doing good now again. The plants I have in my enclosure is directly under my uv light and don't have any problems.