It sounds like you did not water in the plants adequately if this happenned between October and now. It is common to get desication in late plantings of evergreens. Did you flood the holes after burying the root balls most of the way? Or did you do have moist plants and moist ground and just plant them? It is all about getting out any air voids in the soil by mudding them in when you plant broad leaf evergreens late. If you do not do that, the root ball will not draw in water from the surrounding soil. They desicate or stress and are subject to pests and diseases.