Probably the greatest threat to the survival of walnut trees is a root rot, probably a phytophthora fungus. It is not unusual for orchardists on heavier soils to lose a few trees. We had a reminder recently that even older trees are vulnerable. It appears that several trees in the Lincoln University trial block may be suffering from root rot. They are still alive, but may not survive. We have lost trees to this disease in that block before. It is a reminder not to over irrigate. Walnuts do not like wet feet. In our anxiety to maximise growth and influenced, perhaps, by so many dairy and cropping farmers pouring water on throughout the summer we can easily be tempted to over do the water.