in my MI.... most yellow damage... is winter damage ... and some of it doesnt real 'show' until the following summer.. when the heat.. aka water stress happens ... and much of the damage is freeze drying winter winds ....

i know nothing about TX and conifers... if you can track down a conifer collection... or arboretum ... a visit might help you ..

sunburn can be caused by many things.. not necessarily sun itself ... damage occurs to plant tissue when under water stress .. or lack thereof ... hot drying winds ... etc ...

perhaps its too simplistic.. to simply say.. the tissue sun burned ... it would be more correct to ask.. why was the tissue damaged .. causing it to look like it was burned ...

i figured of i just kept typing.. something would come to mind.. i guess i will have to mull this .. and look it up.. i will report back.. if i come up with anything ....

ken

good article mostly pointing toward winter damage... but gives some good reasons why tissue damage occurs ... which you can then interpret toward TX ....

https://laidbackgardener.blog/2015/11/24/preventing-winter-damage-to-conifers/

Thanks Ken. Let me clarify my question a bit. Is there some biological reason why yellow varieties of conifer are more prone to sunburn vs the standard green variety of the same tree? For example I've read that the Gold Rush variety of Dawn Redwood can burn in full hot southern sun yet the standard Dawn Redwood does fine in hot TX sun.

Hi Ash, Its not quite that simple with conifers.
For example, some are yellow year round......
Some flush yellow in the spring and green up in the summer....and some are green all spring and summer until it gets cold and then turn yellow, gold, etc...

Picture from, https://www.coniferkingdom.com/yellow-gold-conifers/ As you can see, they mention that the yellow varieties can burn. On another site about the Maupin Glow (https://plantlust.com/plants/10238/calocedrus-decurrens-maupin-glow/), they go out of their way to point out that it doesn't burn with, "This bright yellow columnar plant will not sunburn." So, there appears to be something about yellow varieties of conifers that are prone to burn vs their standard, wild green varieties. Would love to know why this is, for example does the green protect against UV better than lighter colors like yellow? Just pure curiosity on my part since I keep seeing sunburn/won't sunburn against yellow conifers.

Greetings. I agree with alley_cat. I would only add that cultivars of a species more susceptible to winter burn, such as Picea orientalis, will also be more likely tp experience winter burn. P. o. ‘Skylands’ would be an example of this. I don’t mean to imply the gold foliage doesn’t play any role, but there’s already a tendency for winter burning.

In my experience, summer sunburn does exist. I think the best example of it can be seen in variegated forms when one of the colors is yellow. Before these plants are established, the yellow foliage will burn and drop, while the green foliage is unaffected. I do think that with enough watering, summer sunburn can be avoided in most cases.