Hi Geraldine,

It is hard to say for sure if the tree will make it. Once established, canker is hard to control--especially on the trunk. (If it is located on a branch, for instance, you can often cut off the branch). If the canker has damaged more than 1/3 of the trunk circumference, it doesn't look good for the tree. My suggestion would be to give it some time and see if the tree shows signs of recovery and that the canker doesn't grow. The bacteria that causes cankers is in the soil naturally. Trees become damaged with canker when they are weakened for some reason. The treatment you mentioned for rust in the grass may have contributed to weakening of the tree. I would suggest mulching the area surrounding the tree and making sure that it is watered properly. Weeping willows don't respond well to drought, but you also don't want the ground too wet, as moisture--especially sprinklers spraying on the trunk and canker--could cause the problem to get worse. The tree should be watered deeply when the top 2-4 inches of soil has dried. Let me know if you have anymore questions. I would give the tree a few months to see how it does.