Natural Problems of Globe Willow Trees
Globe willow (Salix matsudana Navajo) is not a weeping willow, but has a round, upright growth habit and a single trunk. Globe willow is native to China, but adapted to the Great Lakes region and desert southwest United States. With a height and spread of 40 feet at maturity, globe willow is one of the first trees to green up in spring. Unfortunately, like most willows, it is notoriously short-lived and prone to a host of naturally occurring problems.
Brittle Wood and Short Life
Plant globe willows for their beauty, but don't get too attached to them. Like other members of the Salix family, globe willow is naturally short-lived, reaching maturity at 30 years and declining after that. Its brittle, soft wood grows fast and is prone to storm damage and splitting at branch crotches. Careful pruning to reduce weight in the canopy can help extend its life. Keep in mind that pruning wounds themselves can invite disease and fungus.
Disease and Fungus
Be on the lookout for bark diseases in globe willow. One of the worst is slime flux disease. Symptoms include a smelly, frothy slime that oozes from branch bark. The ooze is from bacterial activity inside the branch, which forces sap out under pressure. There's no cure for slime flux. All you can do is make sure the tree gets enough water, and prune away the dead and diseased wood wherever you can. Clean pruning tools after use to avoid transmitting disease to other trees.
Cytospora canker also affects globe willow, especially in stressed trees. This fungus attacks twigs and branches, and can even move back into the trunk, killing the tree. The only remedy is to cut out all the diseased wood, keep the soil moist and aerated, and fertilize each spring with 10-10-10 fertilizer to increase nitrogen and reduce stress.
Keep an eye out for bugs on leaves and trunks. Giant willow aphids can attack twice a year, in spring and fall. As they feed on bark and twigs, they exude a sticky substance called honeydew. Sometimes mistaken for ticks due to their large size, giant willow aphids are easily killed by the insecticide imidacloprid.
Insects that feed on other trees, like spider mites, tent caterpillars, grasshoppers and horn worms, also feed on globe willow, but aren't likely to kill one unless their numbers are huge. Weigh environmental concerns before spraying any number of commercial insecticides to kill these insects. You will also likely kill beneficial insects in the process.