Citrus Growers Forum

igor.fogarasi · Posted: Thu 25 Aug, 2011 3:18 pm

while observing the tree i noticed that majority of older leaves look sort of washed out, with a orange colored blush.
i guess they shall turn green soon, as i noticed it happens when the tree is exposed to strong direct sunlight with the temperatures beyond 35.
today, mercury nudged 42C (108F) here in Novi Sad, while real feel temperature was more than a couple of degrees higher.
what am i worried about is that one of them apparently got more yellowing (it's not a real yellowing, it's more like orange to olive-brown gradient).
i assume it might be a kind of sunburn?

what do you guys think it could be?

best regards,
igor

P.S. and no, it's not an advert (AstraZeneca) as you might probably think... Smile

igor.fogarasi · Posted: Sat 27 Aug, 2011 4:21 pm

anyone?
i am not able to decipher what might cause the brownish yellowing shown on the picture above.
could there be more to it than meets the eye? Rolling Eyes

i'm seeking for answer.

best regards,
igor

Millet · Posted: Sat 27 Aug, 2011 4:27 pm

Yes, it looks like sunburn, but the damage is rather slight. The two leaves shown in your photo, and other ones on the tree like them, would still be able to supply photosynthates (the trees food) to the tree. - Millet (508-)

gdbanks · Posted: Sun 28 Aug, 2011 12:17 am

some leaves on my trees are looking like that, though worse. they are also growing new leaves. so i have not been concerned with it. we have been having long hot days here in Texas.

been hoping for a tropical storm to come through.

_________________
looking for cold hardy citrus

http://www.goodreads.com/user/show/6122668-glenn-banks-dds

danero2004 · Posted: Sun 28 Aug, 2011 2:22 am

I don't know if by saying "sunburn" means also intense heat and not only an intense UV rays , but I had this behaviour when the trees were on my windows sill and the leaves that were near the window glass were receiving too much heat . All the leaves were hit by the sun but only those near the glass had that type of "sunburn"

So I say too much heat and not intense UV rays , or both .

gdbanks · Posted: Sun 28 Aug, 2011 4:11 am

i thought glass blocked UV rays.

_________________
looking for cold hardy citrus

http://www.goodreads.com/user/show/6122668-glenn-banks-dds

igor.fogarasi · Posted: Sun 28 Aug, 2011 7:24 am

thanks all for elaborating on this issue!

@danero - i guess you're correct with the assumption. i've also experienced different behaviors of citrus trees in different parts of the backyard. it could be due to vast amount of reflected heat the tree gets. although i keep the pots along with other trees and plants in order to lessen the heat reflection.

@Millet - so you say i should've left those two leaves? i thought leaf or two wouldn't hurt the tree, considering pretty dense foliage for a dwarf orange tree. i didn't know that tree can still leverage even if its leaves have experienced slight to moderate sunburn.

Evaldas · Posted: Sun 28 Aug, 2011 9:06 am

gdbanks wrote:

i thought glass blocked UV rays.

That's true.

danero2004 · Posted: Sun 28 Aug, 2011 2:57 pm

All depends on the type of glass , maybe they reflect the sun UV rays , but the inner layer of glass gets pretty hot in summer days

Stoddo2k11 · Posted: Sun 28 Aug, 2011 9:14 pm

danero2004 wrote:

All depends on the type of glass , maybe they reflect the sun UV rays , but the inner layer of glass gets pretty hot in summer days

Standard glass only blocks about 25-50% of UVA rays while blocking most all UVB.

UVB (315-280nm) - penetrates fewer levels of skin but causes more tanning and skin reddening, strongest in summer months.

UVA (400-315nm) - penetrates deeper into skin but does not cause sunburn, UVA is same strength year round and is 95% of UV radiation reaching Earth.

UVC (280-100nm) - doesn't reach Earth's atmosphere because of the ozone layer but even slight exposure can cause sunburn and prolonged exposure if fatal, 99% of higher is blocked by ozone.

As Danero mentions the type of glass affects the UV exposure. Glass that is tinted, glazed, or coated absorbs more UVA (but allows more UVB through). Also, windshields and many commercial buildings use layers of plastic between glass (which absorbs more UVA).

So, even though we don't see sunburn damage from standard glass it is still a risk to us because of its affect on skin cancer. How Citrus leaves respond to this I don't know. Perhaps if the ozone layer is destroyed then plants won't survive either?

danero2004 · Posted: Mon 29 Aug, 2011 3:45 am

Unless they all are going to adapt to this weather

Yes my windows glasses are glazed with something that is call silver...(layer) and it is LOW-E , is good for the winter when much of the heat from inside stays in . But in the summer the glass is very warm