Are these potted plants? The soil is composted cow manure alone? or mixed in with regular potting soil? If it's straight composted manure I would repot immediately into plain potting soil and water thoroughly, and allow to dry out between waterings.

T

i grew a 3ft avocado tree from a pit. it was doing great while i lives in california then i moved out to nebraska and within days all the leaves fell off and died and now the tree just sits there looking like a skeleton. when i 1st got to nebraska it was below freezing so i kept it in the garage, then it looked like it died now the temp is up and iwater it and it gets tons of sun everyday and still nothing. and also all over the tree, like on the branch times there is some sort of white powdery stuff. what is that? did my tree die? or isthere something i can do for it???