Giant Willow Aphids causing mayhem

Poisoned willows after four years

The honey dew excreted by the Giant Willow Aphid is causing a black soot like substance to form on all the under story plants. This is causing concern as it would be expected to effect the ability of the under story plants to thrive due to substantially reducing their ability to photosynthesize.
We have decided to bring forward our plan to poison off all the willows. The under story seems well enough established to compete with any annual weeds that may grow when the ground is exposed to sun light.
Once dead the willows take about four to five years before they start to fall down so during this time they will still give a certain amount of protection to the under story.

Soot like substance on the under story plants compared to a normal
fern leaf