In the photos below, you will see seven successfully grafted trees before (left) and after (right) pruning. As you look over the photos, take note of a few things. First, the sprouts that are growing from the stock below the graft union have leaves with a reddish coloration. In sharp contrast, the leaves growing from Kanza scions are light green in color. Red pigmentation of emerging leaves is characteristic of juvenile pecan tissue. The leaves growing from the Kanza scions originate from sexually mature tissues in the bud stick and are fully green.
The second thing I noticed about these trees is that vigorously growing stump sprouts seem to inhibit the growth of buds on the scion. Trees 5 and 6 had so much rapid shoot growth coming from below the graft that the buds on the scion were barely sprouting. And remember, all these grafts were made on the same day using Kanza scions.
The differences in scion growth we see in the field are most certainly due to the natural variation in seedling rootstocks. Some rootstock trees will callus over a scion faster than others. Better and faster callusing will allow the scion greater access the the rootstock's energy reserves resulting in enhanced scion growth.
Some rootstocks seem to produce more stump sprouts than others. Rapidly growing shoots produce plant horomones that retard the growth of other buds on the tree. This is why it is so important to prune off stump sprouts.
I grafted over 100 trees this year. Looks like I'll spend a few more days pruning off stump sprouts.