Salix integra ‘Hakuro-nishiki Dappled Willow’, in tree form are grafted to a compatible, strong and straight growing, upright willow trunk. There will be an obvious large lump on the top of the trunk which is the grafted part of the tree. Any shoots from the trunk or roots should be removed as quickly as possible since they are not part of the dappled willow you purchased. Pull off these shoots immediately while young, do not cut them, they will re-sprout if cut. If shoots are left to grow they can eventually overtake the grafted top, these shoots will usually have green leaves.

Hakuro-nishiki Dappled Willows require continuous pruning to maintain the desired form on the grafted part of the tree. The pruning involves cutting the TOP BRANCHES (the grafted-on part) back by 1/3 or even 1/2 every spring, and removing unsightly sprigs can be performed at any time. If you saw the graft off the trunk, you will get either a dead trunk OR the trunk will sprout into whatever kind of willow was used for the trunk. The height of the tree you buy is pretty much the height it will stay, except that the top bushy part will get bigger every year. To give you an idea of how much pruning you will need to do, dappled willows can grow ten feet tall and wide, it is a vigorous and aggressive grower, growing over two feet a year especially when young. Pruning of dappled willow can be done at any time of the year and the tree can be pruned back to any length, as it will set new growth from any wood. Ideally, it should be pruned before growth begins every year. Dappled willow can be kept wispy or airy by pruning it back hard every spring and letting it grow freely throughout the year. Always leave a little wood at the base of the limb pruned to allow for good growth, this will produce knobby growth at the base. Encourage new shoots at the base to grow and then cut out knobby growth on the old limbs from the following spring to keep the core of the bush fresh. Pruning can be performed in late fall but you lose the winter effect of the red stems. Shape your tree as follows: allow each branch to grow until it arches over to the length you desire. Prune repeatedly to the desired length every time the foliage starts to get unruly. Remember to cut the tree back harder at the beginning of following spring.

Dappled willow is relatively insect and disease free. Minimizing stress on the tree is the best way to prevent disease. Willows like water but avoid puddling or pooling water and do not allow them to dry out completely.  Provide some shelter from afternoon sun and you have the perfect growing conditions for your dappled willow.

This reference is for general pruning of a young tree and has some pictures of a weeping tree (not a willow) which may help as well.

http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2761/HLA-6415web%20color.pdf