Low-input management practices for container Ericaceous nursery crops

Low-input management practices for container Ericaceous nursery crops

Summary

A project was established to compare the benfits of using natural versus commercial mycorrhizae in producing azalea plants under two fertilizer rates with and without phytophthora inoculation of the plants. Two nursery sites were selected in south Jersey where nursery growers were involved at each step of the project from preparation of the proposal to evaluation of the propsed system at end of the season. The same project was duplicated at the Rutgers research station at Cream Ridge, NJ. Two azalea cultivars, ‘Delware Valley White’ and ‘Silver Sword,’ were grown in two substrate media mixes (bark-based and peat-based) and fertilized at two fertilizer rates (standard grower’s rate and half the rate) of Nutricote 17-7-8 with four replications and watered with overhead irrigation. Plants were inoculated with either source of mycorrhizae at planting and grown throught the growing season at all sites. Plant dry top and root biomass were determined at harvesting. Root subsamples were collected to assess percent mycorrhizal colonization and percent infection of roots by phytophthora in each treatment.

Preliminary results showed that the addition of natural mycorrhizae at half the rate of fertilizer enhanced top dry biomass of SS plants when grown in peat-based media versus those inoculated with commercial inoculum. Additive effect of using natural mycorrhizae was observed at both fertilizer rates when compared to treated plants with fertilizer only. The addition of mycorrhizae to ‘DVW’ plants did not enhance top biomass but an increase in plant biomass was pronounced in all treatments that were grown in peat-based medium in comparison to those grown in bar-based medium. Root biomass was higher in plants inoculated with natural mycorrhizae than those inoculated with commercial inoculum especially when grown in peat-based medium for both ‘SS’ and ‘DVW’.

In this study, ‘DVW’ plants were more sensitive to phytophthora infection than ‘SS’ plants especially when grown in peat-based medium versus those in bark-based in all treatements. The addition of natural mycorrhizal inoculum at half the fertilizer rate enhnced root biomass and reduced percent infection with phytophthora.

More work is underway to determine tissue nutrient content and mycorrhizal colonization and effect of mycorrhizal inoculum source and rate of fertilizer on sustainability of ericaceous tested plants.

Objectives/Performance Targets

We conducted a comparative study that assessed the impact of commercially-available ericoid mycorrhizal inoculum and naturally-occurring inoculum on plant growth and its quality, the combined benefit from using mycorrhizal fungi and fertilizer rates below industry standards, and the tolerance of plants to disease caused by the water mold pathogen Phytophthora cinnamomi. As a result, we anticipated to develop a feasible, cost effective, and environmentally friendly low-input production system for ericaceous plants.

The objectives of this study are to assess: a) plant growth, b) top and root biomass, b) plant nutrient content, c) extent of root colonization by mycorrhizal fungi from commercially available and natural sources (both before and after overwintering), d) root and crown rot incidence and severity, e) impact of chlorination on mycorrhizal colonization, and f) the economic feasibility of using the proposed sources in producing high quality plants.

Accomplishments/Milestones

We have succeeded in establishing the research projects and involving the nursery growers in this project. Many components of this project were accomplished and questions were addressed in relation of source of mycorrhiza and effect of fertilizer rate and phytophthora inoculation on plant quality. Another set of plants are still grown and overwintered in hoop house at research station to evaluate the mycorrizal colonolization after overwintering with plant biomass. In the coming few months results on mycorrhizal colonization will shed the light on the use of the system for ericaceous plant production.

So far, we have accomplished 80% of the proposed project and we intend to follow up on the project with other proposed projects based on the findings to fine tune the adoption of the sustainable system.

Impacts and Contributions/Outcomes

This project shed the light on understanding the compounded effects of using different growing media and fertilizer rates that could affect plant biomass and to sustain phytophthora colonization in ericaceous plants. Learning about the mycorrhizal colonization percent in each treatment will aid in identifying the benefits of using mycorrhizae from tested sources.

Information on this project was presented at two local presentations and one national presentation. The preliminary results were presented recently at the Annual New Jersey Landscape and Nursery Conference and attended by over 65 people from New Jersey, Pennsylvania, New York, and Maryland.

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