REESources
Check out these excellent resources from Nebraska Extension!
UNL Crop Information
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Institute of Agriculture and Natural Resources
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***Additional Blogs from UNL***
Agricultural/Horticultural:
Nathan Mueller: Crop Tech Cafe Blog
Brandy VanDeWalle, Fillmore Co. Educator Blog
Elizabeth Killinger, Hall Co. Educator Hort Updates
JenREESources's Extension Blog 
At Ritas could part of the problem be half of the trees roots are covered by plastic from the crick?
Phil it may be since you weren’t able to apply the iron sulfate in that area last fall. That may be why we were seeing the response on part of tree and not whole tree.