The primary reason that pecan grafts fail is poor collection and storage of scion wood. It is important to collect scion wood or the cultivars you wish to graft during the dormant season. This is usually late January to early February.
Scions should be cut to length and stored in a moist (NOT WET) material such as moist cedar shavings or wet paper towels or newsprint that has had all the water squeezed out.
The scion wood should then be labeled to the correct cultivar and stored in sealed plastic bags and kept in a refrigerator. Do not allow the scion wood to freeze. This will keep the wood fresh and dormant until spring arrives and grafting can begin.