Mandevilla Plant Leaves Turning Yellow. I place mine in the garage to overwinter keep the pots on the dry side to avoid root rot and force or let them go dormant losing all their leaves. Your plant may have received too much water.
There are several causes for this problem in Mandevilla including. Waterlogged roots are a common reason for the mandevilla plant turning yellow as is dried out soil. 14092005 If the yellowing and wilting coincided with applying the fertilizer then I would suspect an overdose of that.
One might be overwatering.
Too much water can choke the roots so they dont feed the plant adequately. If it was a foliar application you could try rinsing off the leaves. Another possibility could be too little water. When leaves turn yellow it is because they are lacking in pigment chlorophyll.