Question
I have a cottonless cottonwood tree that I planted 3-4 years ago. It grew wonderfully and looked gorgeous until last August (2009) when it became "sick" with some type of disease that caused 60%-75% of the leaves to turn brown and die (the entire crown and 2/3 of mid-level and  bottom branches). The tips of the smaller branches and twigs actually turned brown/black and are dead.

This year it has so far produced no leaves whatsoever on any branches that were affected last year. What do I do? Will it continue to die? Will it recover? It's already 15-20 ft in height.

I was told to spray it with dormant oil this spring but bad and  windy weather held me off and now what leaves are present are too big to allow spraying. I'm not sure the dormant oil would have helped anyway since no leaves have appeared. I'd hate to have to start all over again with a new tree. Any advice would be greatly appreciated.

Answer
 
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Trees - Cottonwood tree

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Expert: Jim Hyland - 8/4/2009

Question
We have lived in Eugene, OR for four years.  Our cottonwood tree has rust spots this year that started end of June- beginning of July, 2009.  It is now dropping yellow, rust covered leaves all the time.  The tree had rust spots when we moved in but the tree had not been properly watered for some time, nor fertilized.  We remedied that, and she has grown several feet. Is this rust a problem to the tree's health? Can we do something to get rid of it?  FYI: she gets her leaves in mid-March, ahead of all the other cottonwoods in the area, and we use Ringers natural fertilizer on the lawn and the tree absorbs it also. We had a rainy spring, and have just had a couple of weeks with above average heat. We could use your help, this is worrying us.  Thank you!

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Answer
Sounds like cottonwood leaf rust. Yellow or orange pustules, containing spores, form on the under-surface of the leaves in midsummer. All rust diseases need two different hosts species to complete the life cycle. The orange pustules (uredia spores) are the summer reproductive state of the fungus. They are followed by dark brown pustules (telia spores) which develop in fall and winter. Her in the South, the alternate host (larch) is not present in the forest, and the fungal life cycle is reduced to the urediaurediospore cycle only. There I would think there are conifer species growing in the area that would act as the alternative host. Some families are immune to rust infection and disease-free trees or groups of trees often occur in the midst of other heavily infected trees. That maybe why one tree is infected and the other is not. Treatment in a yard situation is to rake the fallen leaves and destroy them cutting down the amount of spores which may reduce the amount of yellowing next year. The extent of the yellowing will depend on the weather when the spores from the conifers are germinating (damp cool weather are ideal for the spores).
If the majority of the leaves are effected for several years the rust can cause some growth loss. These is not a fungicide that can be used to prevent the disease.--the removing of the leaves and destroying them will reduce the spores for next year.

Here is a web link to more information on Cottonwood Rust:
http://www.for.gov.bc.ca/hfp/publications/00198/Cottonwood_leaf_rust.htm