Phytophthora Root Rot Information Sought for New Soil Microbe Research Project

  • Apr 01, 2019

Dr. Mike Coffey, Professor of Plant Pathology, UC Riverside, is working on a project to test for which microbes in avocado soils suppress Phytophthora root rot using a model greenhouse system and he needs the help of California avocado growers. If you are a grower in Ventura or Santa Barbara Counties, Dr. Coffey would like to talk with you to better understand what has and has not been working with respect to Phytophthora root rot management.

He would like to understand what your root rot management practices have been on mature trees and replants. Specifically, do you prune root rot trees along with any chemical control programs? If so, how do you time the pruning — prior to or simultaneous with chemical application — and what chemical treatments are you using? How long have you been treating the same trees? Have you observed any loss of treatment efficacy over time? What other practices do you integrate into your Phytophthora management program — irrigation modifications, mulch application, fertilizer/nutritional programs, etc.?

With respect to replant trees, what rootstocks are working well for you? Do you plant replant trees on mounds? What chemical program do you use for replants and is your replant program successful? 

In some cases, researchers have noted that avocado trees do well despite the presence of Phytophthora. Traditionally such situations, especially where individual trees are involved (sometimes referred to as escape trees), have been attributed to better drainage at that site, or a more resistant root system. However, Dr. Coffey’s research project will examine whether the soil microbes, in these situations, are more suppressive of Phytophthora. If that were the case, identifying and harnessing those microbes might lead to a more effective treatment, especially where replanting is involved.

Therefore, Dr. Coffey is especially interested in speaking with growers who have observed areas of their grove where trees do well despite the presence of Phytophthora and thus they seldom do any treatments. He also is interested in reports of any trees that appear superior in their tolerance to Phytophthora.

If you would like to help Dr. Coffey with this project, please reach out to him. He can be reached at

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