If your trees have lost all of their leaves but there are still patches of green leaves on them, they are most likely under attack by mistletoe.
Mistletoe is a parasite that slowly kills trees.
How It Spreads: The mistletoe is dependent on birds dispersing its seeds. Birds feed on the fruits (drupes) of the mistletoe. The seeds are sticky and attach themselves to the birds. The birds dislodge the seeds by rubbing against other trees. Mistletoe is not very host specific and can be seen growing on a wide variety of trees and shrubs.
Mistletoe with leaves are considered to be only partial parasites because they manufacture their own carbohydrates through photosynthesis, but they still depend on host trees for water, minerals, protein, inorganic ions, sugars, amino acids, and hormones from the tree’s xylem and phloem.
Reality Decoded 
Interesting… the things you never knew you needed to know.
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I know what you mean.
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I prefer step fungus.
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Wow
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I was under the assumption that mistletoe was also poisonous to humans?
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It is toxic if eaten but can be medicinal if processed correctly
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Ok, yeah, thats right. Interesting for sure.
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Interesting.
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Eek.
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