ARS | Publication request: Eradication of Rotylenchulus reniformis from a volcanic cinder medium using steam sterilization

Submitted to: Nematropica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 11, 2012
Publication Date: N/A

Interpretive Summary: Reniform and burrowing nematodes are regulated quarantine pests. Nurserymen in areas where these nematodes exist must follow strict certification requirements in order to export to markets where the pests are not established. Recent rejections of interior foliage shipments from Hawaii to California were found to be caused from contamination of volcanic cinder by reniform nematodes. Historically cinder has been free of plant parasitic nematodes and utilized by certified nurseries as potting media. To resume shipments of potted plants, Hawaii growers are now required to steam sterilize cinder before use. Trials were conducted to test the efficacy of 2 steam treatment systems, one using a 2.2 cu yd capacity steam cart and the other an innovative modification to a dump truck bed using a manifold and a large capacity steam generator. Packets of cinder were inoculated with reniform nematodes and infected sweet potato roots. The packets were placed in various locations throughout the media and monitored with temperature probes during the sterilization process. No live nematodes were recovered as long as the steam completely diffused through the cinder. It was confirmed that steam treatment is an effective method of disinfesting volcanic cinder of plant parasitic nematodes. Shipments of interior foliage plants have resumed without incident since adopting this sterilization technique.

Technical Abstract: In Hawaii, reniform nematode, Rotylenchulus reniformis, damages many agricultural crops and disrupts plant trade because of the regulations imposed against this pest by the state of California and other national and international markets. Nurseries in Hawaii must follow strict certification requirements to export potted plants to these markets where R. reniformis is not established. Mined volcanic cinder, utilized as a potting medium, may contain reniform nematode and needs to be disinfested for use by nematode certified nurseries. Two steam treatment systems of different capacities were evaluated for their efficacy to disinfest the cinder of R. reniformis. The low capacity system consisted of a portable steam generator connected to a steam cart with a media volume of 1.68 m3. The large capacity system consisted of a dump truck bed modified with an intake manifold and steam distribution pipes connected to a large capacity steam generating boiler to sterilize a 24.5 m3 load of media. Packets of nematode-infested cinder containing R. reniformis-infested roots of Ipomoea batatas were buried in various locations and different depths in the cinder contained in the two steaming systems. Temperature probes were placed inside or adjacent to the packets and observed during the sterilization process. The steam did not penetrate and distribute in the medium at a consistent rate in both steaming systems resulting in cold spots. These were identified and monitored to ensure that treatment time was sufficient to reach target temperature throughout the medium mass. Once the steam was evenly distributed both systems were successful at eradicating all live R. reniformis.