Impact of non-fumigant nematicides on reproduction and pathogenicity of Meloidogyne enterolobii and disease severity in tobacco

Authors: ALAM, MD - Clemson University; KHANAL, CHURAMANI - Clemson University; ROBERTS, JOSEPH - Clemson University; Rutter, William

Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2023
Publication Date: 6/5/2023
Citation: Alam, M.S., Khanal, C., Roberts, J., Rutter, W.B. 2023. Impact of non-fumigant nematicides on reproduction and pathogenicity of Meloidogyne enterolobii and disease severity in tobacco. Journal of Nematology. 55(1). HTTPS://DOI.ORG/10.2478/jofnem-2023-0025.
DOI: https://doi.org/10.2478/jofnem-2023-0025

Interpretive Summary: The guava root-knot nematode (GRKN) is a highly virulent nematode that has been spreading across the southeastern US, where it infects most cultivated crops. Several different pesticides are commercially marketed to help manage root-knot nematodes in tobacco growing operations, but their effectiveness can vary depending on the nematode species present in the soil. No one knows how well the maximum allowable application rate of these pesticides can control GRKN on tobacco roots. In this study, two pesticides (Oxamyl and Fluensulfone) were fount to significantly reduced the number of GRKN eggs and juveniles, while also reducing the amount of nematode galling on the plant roots. However, neither application significantly improved above ground plant growth compared to controls. A third pesticide (Fluopyram) did significantly enhance plant shoot growth and reduced nematode galling, but showed only a modest reduction in nematode eggs and juveniles. The last pesticide (Majestene®) showed no effect on GRKN or plant growth. In summary, three of the four pesticides tested in this study reduced the numbers of GRKN in the soil and reduced the root galling caused by this nematode. Follow up studies need to be conducted in GRKN infected fields to confirm these results. The results of this research could help tobacco growers and extension agents in the southeast make informed decisions about how to manage GRKN in the field.

Technical Abstract: Studies were conducted in a growth room environment to evaluate the impact of non-fumigant nematicides at their maximum allowed rate on the reproduction and pathogenicity of M. enterolobii as well as on disease severity in tobacco. Treatments involved three non-fumigant chemical nematicides (oxamyl, fluopyram, and fluensulfone), a biological nematicide derived from Burkholderia, and a non-treated control. Oxamyl and fluensulfone significantly suppressed the nematode reproduction relative to the control, with oxamyl suppressing 50% of eggs and 88% of J2, and fluensulfone suppressing 71% of eggs and 86% of J2. Fluopyram also suppressed nematode reproduction, although not at a significant level, with the suppression being 26% and 37% for eggs and J2, respectively. The disease severity assessed as a measure of gall index was also significantly reduced by the application of non-fumigant chemical nematicides. The most significant reduction of disease severity was achieved by the application of fluensulfone (64%), followed by oxamyl (54%) and fluopyram (48%). Except for fluensulfone, which significantly reduced the root biomass, none of the nematicides significantly impacted root and shoot biomass. The biological nematicide did not significantly affect nematode reproduction, pathogenicity, and disease severity. Results from the current study suggest that the non-fumigant chemical nematicides are promising tools for managing M. enterolobii in tobacco. However, further studies on efficacy improvements are needed as complete suppression of the nematode was not achieved with the use of the maximum allowed rate.