The two most dreaded diseases affecting the root of walnut. Produced by two fungi, the first attacks the roots of the tree and the second, mainly the root collar.

Not all rootstocks are equally sensitive. Currently are being investigating more resistant rootstocks. Juglans Nigra is more resistant to Phytophthora and J. Regia is more sensitive. A rootstock that is highly resistant is Pterocarya stenoptera, currently under study, which has little affinity with some varieties of walnut. In the future, the availability of new rootstocks, will enable planting walnut trees on soils that currently are not recommended, for excessive moisture or for having previously plantations. This problem limits the use of plants from "in-vitro" multiplication because being J.Regia on its own roots are very sensitive.