Project: 2007-03. Report - Management of Phytophthora in radiata pine seedlings (2007–03)
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Date: 2008 Author: HortResearch Publication: Report Project reference: 2007-03 Report is available online |
Executive summary:
BACKGROUNDBlock 4 at Te Ngae nursery has recently suffered losses among Pinus radiata seedlings due to Phytophthora root rot. The purpose of this project was to investigate chemical and biological options under controlled environmental conditions for their ability to control root rot of P. radiata seedlings, caused by Phytophthora cinnamomi. This project complements FRST funded studies conducted at Te Ngae nursery where various integrated programmes are being evaluated for their ability to manage root rot under field conditions.
SUMMARY
A series of four pot trials was conducted to evaluate selected chemical products and a biological agent, as potential alternatives to metalaxyl to control Phytophthora root rot caused by P. cinnamomi in Pinus radiata seedlings. Two soil treatments, Trichoderma and humatelime, and one foliar treatment, Foli–R–FosŪ, were evaluated alone and in combination in order to identify potential additive benefits with regard to disease control. Treatments were applied
to the soil and/or to seedlings before transplantation of seedlings into potting mix that was infested with P. cinnamomi. Seedlings were maintained in conditions that were highly favourable for the development of Phytophthora root rot for the duration of the experiment. RidomilŪ Gold MZ (a.i. metalaxyl) completely suppressed root rot when applied to infected potting mix at a rate of 460 mg/L or higher. However, when applied at concentrations approximating the recommended field rate (33 mg/L), RidomilŪ Gold MZ was not effective and disease incidence reached 65% after three weeks compared with 85% in the untreated control. Trichoderma and humate–lime, whether applied alone or in combination, did not control root rot. Foliar application of Foli–R–Fos alone reduced root rot incidence by up to 60%, but the efficacy of this treatment was not consistent among experiments. Combination treatments involving Foli–R–Fos with humate–lime or with Trichoderma generally resulted in lower disease incidence than the component treatments applied alone. Although the differences in disease incidence were not statistically significant, there is an apparent trend indicative of an additive benefit that merits further investigation.
The treatments under investigation in this study were also evaluated in FRST funded trials at Te Ngae nursery between 2006 and 2008. In each season, root rot symptoms developed
following root pruning suggesting a link between this activity and root infection. RidomilŪ Gold MZ provided moderate control (8% seedling mortality) when applied one week after
root pruning, but was ineffective (21% mortality) when applied at seedling emergence. Poor control at emergence was attributed to dilution or degradation of metalaxyl during the period between application and root pruning. The most effective treatment was Foli–R–Fos, which reduced mortality from root rot to 0.14% when applied at fortnightly intervals commencing one month before root pruning (seven applications). Results of the field trial study have been
prepared for publication and extracts from the manuscript can be found in Appendix 1.
Tony Reglinski
The Horticulture and Food Research Institute of New Zealand Ltd
HortResearch Ruakura
Private Bag 3123,
Waikato Mail Centre
Hamilton 3240
NEW ZEALAND
Tel: +64–7–959 4430
Fax: +64–7–959 4431
Fax: +64–3–904 7301
Email treglinski@hortresearch.co.nz
Report is available online
