Table of Apple Rootstock Susceptibility to Phytophthora spp.

Apple Phytophthora root, crown, or collar rot has caused extensive death of apple trees in many eastern orchards during the past two decades. It often occurs on trees between 3 and 8 years of age grown on Malling-Merton 104 (MM.104), MM.106, and, to a lesser degree, MM.111 rootstocks. The disease often affects low areas of orchards having heavy, poorly drained soils, but it can affect all orchard sites if trees are first infected in the nursery. This table illustrates susceptibility of numerous apple rootstocks to Phytophthora spp.

Apple rootstock cultivar Phytophthora resistance rating*
Bud.9 R
C-G 210 R
Geneva 11 MR
Geneva 16 MR
Geneva 30 R
Geneva 65 R
Mark (MAC.9) MR
M.104 HS
M.106 HS
M.111 S-MR
M.2 MR
M.26 S-HS
M.27 MR
M.4 MR
M.7 S
M.7a S
M.9 MR
Ottawa 3 R
P.2 R
P.22 R
Seedling MR
*R = resistant. No control needed.

MR = moderately resistant. Specific control needed under high disease pressure.

S = susceptible. Control usually needed where disease is prevalent.

HS = highly susceptible. Control always needed where disease is prevalent. These cultivars should receive first priority when control is required.

(Note: Because a number of Phytophthora species cause root, crown, and collar rot, it is difficult to make absolute statements about the relative susceptibility of different rootstocks to these diseases.)

See Phytophthora root, crown, and collar rot for more information.

References and Resources

Fruit Disease Focus article by Dr. Wayne F. Wilcox.

Anonymous. 1997. Introduction to the Oomycota (Water Molds). University of California Museum of Paleontology.

Ellis, M. A. 1997. Phytophthora Root and Crown Rot of Fruit Trees. The Ohio State University Extension Factsheet HYG-3029-95.

Teviotdale, B. L., and Gubler, W. D. 1995. Phytophthora crown and root rot. UC Pest Management Guidelines, University of California Statewide Integrated Pest Management Project.

Prepared by A. R. Biggs, K. D. Hickey and K. S. Yoder