Hot Water Drench Treatments for the Control of Radopholus similis in Rhapis and Fishtail Palms

Abstract

Exporters of potted nursery stock face strict quarantine regulations against the burrowing nematode, Radopholus similis. Currently, there are no treatments approved by quarantine authorities to disinfest plants of R. similis. Interceptions of the nematode lead to significant economic loss and curtailment of trade, therefore hot-water drench treatments were investigated for quarantine utility. Drenches with 50 °C water were applied for 10 to 16 minutes to two economically important palm species, rhapis (Rhapis excelsa) and fishtail (Caryota mitis). Plants were inoculated with 5,000 mixed life stages of R. similis and allowed to establish for 14 weeks before drench treatments. In rhapis, a moderately good host to R. similis, a 16-minute hot water drench had high efficacy, achieving 99.6% mortality. In fishtail, a poor host, all treatments longer than 10 minutes at 50 °C eliminated R. similis from the plants. Probit regression estimates of the LT99, were 16.9 and 10.3 minutes respectively. However χ2 goodness-of-fit tests were significant (χ2 = 21.136, df = 3, p < 0.0001) for rhapis. Since most observed values were between the 95% fiducial limits, this suggests that the large χ2 value was caused by variability in response or insufficient repetitions rather than an inappropriate model. A χ2 statistic could not be computed for fishtail because poor host status led to variances that were nearly equal to zero. The high efficacy of hot water drenches for the control of R. similis is approaching the Probit 9 standard of 99.9968% mortality required for approval as a quarantine treatment.