Guy sorry I took so long but this is the write up I did for a client, what do you think.
Willow blight is a name usually given to two separate fungal diseases occurring at the same time on willows. Separately the diseases are willow scab (Venturia saliciperda) and black canker (Glomerella miyabeana).
Both the scab and black canker fungi overwinter in diseased twigs and branches and are spread by microscopic spores during the spring and summer. Willow scab spores are produced on the under surface of dead leaves and on dead twigs, while those of willow black canker usually form on dead twigs and on twig branch cankers.
It is very helpful, as well, to rake up fallen leaves and collect dead twigs and branches on a regular basis. All diseased material must be trashed or destroyed so that infected parts do not re-infect the tree.
Willow blight is spread by light rain and mist, and gardeners should therefore not hose down or power wash their willows unless the weather is forecast to be hot and dry. Watering should only be carried out in the morning hours.
Willow blight shows up where willow trees are planted too close together, as in a shelterbelt. Crowding reduces air circulation and increases humidity within the trees, fostering ideal conditions for the blight to develop. That is not the issue with your trees but something to keep in mind.
With last summer’s road construction out side your house being on a gravel road and everything getting thickly coated in dust, led to you washing off the trees everyday this kept the crown in a wet condition that was ideal for the growth and spread of this problem.
Black canker and willow scab can be controlled through a combination of cultural and chemical treatments. Chemical treatments consist of properly timed fungicide applications(of Daconil Ultrex, in the spring I believe) to reduce pathogen infection and symptom development. Pruning out infected stems and twigs and fertilization are effective cultural treatments that will reduce disease severity and improve tree vigor.
