Evaluating the Potential of Cover Crops to Mitigate the Impact of Phytophthora in Macadamia Orchards

Project Overview

Project Type: Farmer/Rancher
Funds awarded in 2021: $24,574.00
Projected End Date: 12/31/2023
Host Institution Award ID: G357-21-W8613
Grant Recipient: Island Harvest Inc.
Region: Western
State: Hawaii
Principal Investigator:
Andrew Trump
Island Harvest Inc.


  • Nuts: macadamia


  • Crop Production: cover crops
  • Pest Management: cultural control
  • Production Systems: organic agriculture

    Proposal summary:

    The Hawaii macadamia industry had a farm gate value of $48.8 million dollars in 2019-2020, making it one of the highest value crops in the state of Hawaii (USDA NASS 2019). But in recent years macadamia farms in Hawaii have experienced devastating tree losses due to soil-borne root infections of Phytophthora spp. As farmers in Hawaii both replant and manage existing orchards, sustainable approaches to combat the impacts of Phytophthora root rot are needed. 


    This project will evaluate the potential for integrating cover crops in existing orchards and prior to replanting orchards to mitigate the incidence and effects of Phytophthora root rot on macadamia nut trees. It is well known that incorporating cover crops into farming systems can improve soil structure, add soil organic matter, provide nutrients, and encourage soil microbial diversity. However, research on the efficacy of establishing cover crops in perennial orchard systems with minimal disturbance to soil health so as to maximize soil-borne pathogen suppression is needed. Island Harvest Inc., operating over 700 acres of orchard, plan to demonstrate the use of an AerWay overseeder to plant two cycles of cover crop mix in their orchards to prove the concept of conservation tillage cover cropping system could lead to the mitigation of Phytophthora root rot hampering the macadamia industry in Hawaii statewide. The results of this project will be disseminated to macadamia nut growers through the University of Hawaii extension publications, field days, and workshops at Hawaii Macadamia Nut Association meetings.

    Project objectives from proposal:


    1. Quantify the mitigation of Phytophthora incidence and severity when integrating cover crops in macadamia orchards


    1. Quantify other soil health benefits of integrating cover crops in macadamia orchards


    1. Estimate the economic return of controlling Phytophthora using cover crops


    1. Educate macadamia farmers on using cover crops as a method for sustainable cultural control of Phytophthora.
    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.