Hello Kathleen,

     From the picture you have sent , I believe you may have Hemlock Wooly Adelgid. It would be best for you to contact a good tree service or An Arborist for treatment of all four trees . 

     Please see the link below for more information.

 https://extension.psu.edu/integrated-approach-to-hemlock-woolly-adelgid-mitigation

Hello Kathleen.

     I am glad to hear you are having a professional look at your trees. In part answer to you question about fertilizer, it is best to fertilize in the early spring before new growth begins. You will want to use a slow release fertilizer and you can spread it beneath the trees keeping the fertilizer about 4 inches away from the trunk of the tree. You will also want to use a fertilizer lower in nitrogen. It has been found that more nitrogen may increase the infestation of scale and adelgid.

     I will defer to you arborist or plant professional as to the correct mixture of fertilizer. Since it appears you have a heavy infestation the professional may wish not to apply nitrogen at this time.