Weeping Willow

While the tree is bare and you can see the frame, train young willows to a single central leader with wide branch crotches. Remove crossing limbs and any branch that is getting heavy on a narrow, poorly formed attachment, and lift the skirt for clearance underneath as the canopy drapes. Willow breaks either at the crotch, where the branch collar forms poorly, or through the wood itself, which is simply weak - so snow and ice loads split limbs that were never given a strong attachment.

Cut the year's rods during the dormant season, any time after leaf fall and before growth starts, roughly November through March depending on your zone. Cut as close to the ground as possible, and cut the stool every single year rather than letting rods stand a second season. Go carefully for the first couple of seasons so you do not uproot young plants. Cornell is explicit that willow grown for weaving has to be harvested every year so the rods stay pliant and unbranched. First-year rods are often too short to weave and are better used to expand the planting; by the second season the stool should give plenty of supple rods in the 4 to 9 foot range.

Set willows out as soon as the soil is frost-free in spring. Dormant cuttings can be collected any time over winter and held in moist sand or sawdust in a cool spot until planting (Cornell Small Farms, https://smallfarms.cornell.edu/2013/06/willow-a-new-old-crop/). Choose a low, wet spot and keep the tree well away from water lines, sewer laterals, septic fields, wells and foundations. NC State Extension warns that this tree's shallow, invasive root system 'can create havoc on your sewer and water pipes,' and rates the tree high-maintenance for breakage of its weak wood, spreading roots and leaf litter — so a bad location becomes a demolition bill on a tree that UF IFAS puts at only about thirty years of life.

On a tree with a history of spring twig dieback, spray myclobutanil when the new leaves first appear, and repeat at 10 to 14 day intervals while spring weather stays wet. Shut off overhead irrigation and open the canopy so foliage dries faster. Venturia saliciperda infects only young, expanding leaves, then travels down the petiole into the twig and girdles it - older leaves and twigs resist it. The fungicide has to already be on the leaf before the first spring rain splashes spores onto it.

Weeping willow wants soil that stays very moist and will happily take occasional flooding and standing water. Water deeply whenever a dry spell sets in rather than letting the tree ride it out. Extension guidance for willow blight puts drought watering at the centre of control: a willow that goes dry sheds its leaves and loses the vigour that holds off scab, black canker and the canker fungi, all of which take hold on weakened wood.

Check leaf undersides for small raised pustules, 1 to 2 mm across, orange or brown. If rust returns year after year, the answer is genetic: replant with resistant varieties and grow them in a mixed stand rather than escalating to fungicide. Melampsora leaf rust is the most damaging disease of shrub willow and moves fastest through cool, moist summers, which is why northern plantings get hit hardest. Resistance is under strong genetic control, and a mixed stand puts resistant plants in the way as a physical barrier to spore movement.

When small shiny black beetles and their grub-like larvae start skeletonizing the leaves, spray Bacillus thuringiensis var. san diego with ultrafine horticultural oil, timed to the young larvae. Expect to repeat as the next generation hatches. The beetle runs at least two generations a year and the overwintered adults do not all emerge at once, so one spray leaves eggs and late arrivals behind - and Bt only kills larvae that are still young.

Prune out and dispose of twigs carrying dark sunken cankers, and rake up and remove fallen leaves and twigs rather than leaving them under the tree. Get the leaf litter out before spring growth begins. Willow blight is scab and black canker infecting the same tree at once, and both fungi overwinter on the fallen leaves and infected twigs sitting under the canopy - that litter is the spore source that reinfects the new leaves next spring.