???Forest disorders???

[caveman]

In just a few weeks, my students will be traveling to Kentucky to participate in the National FFA Forestry Contest which will be held at Bernheim Forest.  While trying to learn to identify the disorders on their list, they (and myself) are having difficulty determining the difference between these three.
1.  Sun scald
2.  Chemical damage
3.  Air pollution

Is there a reliable indicator to determine, by looking at the foliage, which of these three cause certain characteristics in leaves?
Thanks,
Caveman

[WDH]

I cannot be any help on this one. 

[beenthere]

I would doubt one could tell... albeit if the person setting up the test thinks he/she knows how, then best to find out what they perceive to be the difference.   ;D

[Texas Ranger]

In just a few weeks, my students will be traveling to Kentucky to participate in the National FFA Forestry Contest which will be held at Bernheim Forest.  While trying to learn to identify the disorders on their list, they (and myself) are having difficulty determining the difference between these three.
1.  Sun scald
2.  Chemical damage
3.  Air pollution

Is there a reliable indicator to determine, by looking at the foliage, which of these three cause certain characteristics in leaves?
Thanks,
Caveman

The only sun scald I have seen is in the cambium, not leaves.  With the exception of japanese maple.  Texas sun plays havoc with exposed portions of crown, a product of the heat, I think.

I had one case of chemical damage, I could not swear there was anything other than needle caste, yet it was a release of a silicon product that drifted into a plantation.

Air pollution. Never saw a case.

In all, I have not a clue.

[mesquite buckeye]

Sunscald on leaves can be seen in milder cases as bleaching. The leaves that are shaded by other leaves will be greener where overlapping leaves protected them. This is generally reversible.  More severe cases will show up especially on drought stressed plants. Leaves on the sun exposed side of the tree will actually get sunburned. This is quite common on citrus in Arizona. Sunscald is fairly common on thin barked branches that get exposed to sun, especially during hot weather. This is a heat injury, as previously stated. It will be most obvious on the south and upper sides of branches up to several inches in diameter. The bark frequently is actually killed by this. Often the problem gets exacerbated by excessive pruning or following a defoliation event.

Chemical injury, particularly meaning herbicide injury will often be expressed as chlorotic (yellowing) new leaves and often as defoliation and death of branches and roots, as well as the intervening bark on the side of the tree where the offending chemical was applied. Superficially this can look like a trunk sunburn, but the alignment of damaged plant parts is distinctive, as well as the trunk bark death is not confined to only south or southwest facing directions.

I have not  seen pollution injury, except in photos, but it has to get pretty nasty to get them. Think LA in the sixties. What I have seen is sort of blotchy burnish injuries that look a little like some of the bacterial leaf blights.

Hope this helps.

[WDH]

As far as air pollution, a number of trees in the higher elevations in the Great Smokey Mountains have been killed by acid rain.

[caveman]

Thanks a lot.  The knowledge of the folks who frequent this forum never ceases to amaze me.
Kyle

[Texas Ranger]

Sunscald on leaves can be seen in milder cases as bleaching. The leaves that are shaded by other leaves will be greener where overlapping leaves protected them. This is generally reversible.  More severe cases will show up especially on drought stressed plants. Leaves on the sun exposed side of the tree will actually get sunburned. This is quite common on citrus in Arizona. Sunscald is fairly common on thin barked branches that get exposed to sun, especially during hot weather. This is a heat injury, as previously stated. It will be most obvious on the south and upper sides of branches up to several inches in diameter. The bark frequently is actually killed by this. Often the problem gets exacerbated by excessive pruning or following a defoliation event.

Exactly what I have seen on the off site Japanese Maple.

[Autocar]

We have alot of herbicide posining around here and the leaves will only show the veins and the rest of the leaf is a off color or the edges will curl up and they almost feel like leather. Ive been cutting dead white/swamp/bur oak for the last eight to ten years. Yesturday I looked at 51 swamp white oaks averaged 300 plus feet to the tree and out of the 51 there was only 7 that was alive. Every landowner asks me whats killing them I can't come up with a answer so this past week I pulled soil samples and took them to a lab that test soil. Maybe this will give me a answer.

[mesquite buckeye]

Do you know which herbicide was used?

Generally with herbicide injuries we are talking about soil active chemicals or sometimes spray drift with things like 2,4, D.

Roundup injury to trees is uncommon except with sloppy spraying practices and small trees.

Generally herbicide injuries have the chlorosis thing in common. However, each herbicide will have somewhat different specific symptoms.

[Autocar]

I don't know the names of any of them but the one they spray just before they no till soybeans in and it raises out of the ground at night and drifts it hammers red buds and young anything. Then the other they spray corn with and it will turn the leaves brown and they just dry up. Around here they spray with planes helicopters and big four wheel spraying rigs. Wind dosen't make the co-ops much difference when you complain there answer is we have thousands of acres to get done and only have a small window to get it done. Anymore I get upset but just turn my back on all of it. You can only hit your head against a wall so long then I throw the towel in. Are county and Mercer cty has the highest cancer cases in the state I believe, and its all big agriculture around here don't know if thats why but worth looking into I think.