Last week we discussed what fumigants are and how they work. We also presented a summary of recent research that evaluated the effect of metam sodium on tomato yield. Our conclusion from that research was that metam sodium is not an effective tool for improving yield associated with root rot and vine decline under field conditions. In this article, we'll review research results from older research in Ontario, as well as peer-reviewed research from locations outside Ontario.

Previous Ontario research results

The late Dr. Ron Pitblado, who worked as a College Professor at the Ridgetown College of Agricultural Technology and later Ridgetown Campus of the University of Guelph, conducted research on metam sodium in processing tomato fields from 1989 to 1991. We dusted off Dr. Pitblado's industry research reports from that time and summarized the results in Table 1. Metam sodium was applied using standard industry practices at the time, which are quite similar to the practices in use today. The target pests were root lesion nematodes and the fungal pathogen Verticillium dahliae. Dr. Pitblado also found results with metam sodium to be inconsistent. For example, in 1990, all 5 sites that had pest levels above the treatment threshold responded with a yield increase following fumigation. However, of the three test sites evaluated in 1991, none produced a yield response to fumigation, even though all three were above threshold for both target pests.

Table 1. Summary of results of research conducted by Dr. Pitblado on processing tomatoes in Essex County, Ontario, 1989–1991.
Year and number of sitesTarget pestEffect on pestEffect on yield
Year: 1989
6 sites		Root lesion nematodeReductionNot measured
Year: 1990
5 sites at pest threshold(s)		Root lesion nematode, Verticillium dahliaeNot measuredIncrease at all 5 sites
Year: 1990
5 sites below pest threshold(s)		Root lesion nematode, Verticillium dahliaeNot measuredNo effect at 4 of 5 sites
Year: 1990
31 sites (10 at pest threshold levels)		Root lesion nematode, Verticillium dahliaeReduction with pooled data, but not at all individual sitesNot measured
Year: 1991
3 sites (all at pest threshold levels for both pathogens)		Root lesion nematode, Verticillium dahliaeNot analyzedNo effect at any site, possibly because of poor Verticillium control

Research results from other locations in North America

Research results from other locations in North America are also inconsistent. Table 2 summarizes results where metam sodium was applied using soil injection methods, whereas Table 3 summarizes results using other applications methods.

Table 2. Summary of research results on the effectiveness of soil injection-applied metam sodium at reducing soil pest populations or increasing tomato yield at various locations in North America.
Location (source)
Target pest		Application methodReduced disease?footnote 1Increased yield?footnote 1
Florida (McGovern et al., 1998)
Fusarium oxysporum f. sp. radicis-lycopersici		Injection chisel, 6 per bed, 4-in chisel spacing, 8-9 inch depth0 of 2 sites0 of 2 sites
Florida (Csinos et al., 2002)
Rhizoctonia solani, Pythium spp., Fusarium spp., Aspergillus spp., Penicillium spp. and others		Injection chisel, 6 per bed, 12-inch spacing, 8-inch depth + sealed with polyethylene filmReduction in pathogen populations in soil at 3 of 3 sitesNot measured
California (Hartz et al., 2005)
Verticillium dahliae, Fusarium spp.		Injection shanks, 4 per bed1 of 1 sites with V. dahliae0 of 2 sites
Table 3. Summary of research results on the effectiveness of various metam sodium application methods at reducing soil pest populations or increasing tomato yield at various locations in North America.
Location (Source)
Target Pest		Application methodReduced disease?Increased yield?
Florida (McGovern et al., 1998)
Fusarium spp.		Drip chemigation0 of 2 sites except in one case where high rate reduced severity but not incidence0 of 2 sites
Florida (McGovern et al., 1998)
Fusarium spp.		Pre-bed spray1 of 1 sites reduction in incidence but not severity0 of 1 sites
Florida (Csinos et al., 2002)
Rhizoctonia solani, Pythium spp., Fusarium spp., Aspergillus spp., Penicillium spp. and others		Spray-till + plastic mulch3 of 3 sites reduced pathogen population in soil, depending on days of film coverNot measured
Florida (Gilreath et al., 2004)
Fusarium oxysporum f. sp.radicis-lycopersici, various root-galling nematode species		Spray-till + plastic mulch1 of 2 sites for F oxysporum; 2 of 2 sites for nematodes2 of 2 sites
Florida (Csinos et al., 2000)
Rhizoctonia solani, Pythium spp., Fusarium spp., Aspergillus spp., Penicillium spp. and others + ring, root-knot, stubby-root, and spiral nematode		Spray-till + plastic mulch2 of 2 sites reduced pathogen populations in soil; 0 of 1 sites reduced root-knot nematode population but not damage; 1 of 1 sites reduced root-knot nematode damageNot measured
North Carolina (Sydorovych et al., 2008) Verticillium dahliaeDrip chemigationIncrease in financial returns compared to fumigation with MeBr (6-year study)-
North Carolina (Sydorovych et al., 2008) Verticillium dahliaeSpray-tillFinancial returns equivalent to use of MeBr (6-year study)-
Florida (Locascio et al., 1997)
Rhizoctonia solani, Macrophomina phaseolina, Fusarium spp., root-knot nematode		Drip chemigation2 of 3 sites for fungal pathogens; 1 of 2 sites for root-knot nematode damage2 of 3 sites
Florida (Locascio et al., 1997)
Rhizoctonia solani, Macrophomina phaseolina, Fusarium spp., root-knot nematode		Spray-till + plastic1 of 3 sites for fungal pathogens; 0 of 2 sites for root-knot nematode damage0 of 3 sites

So, why the inconsistency? We will discuss factors that can contribute to inconsistent results with fumigation in Part III of this series, which will appear in a future issue of Hort Matters newsletter.

References

  • Csinos, A.S. et al. 2000. Methyl bromide alternatives in tobacco, tomato and pepper transplant production. Crop Protection. 19:39-49.
  • Csinos, A.S. et al. 2002. Application and crop safety parameters for soil fumigants. Crop Protection. 21:973-982.
  • Gilreath, J.P. et al. 2004. Soil fumigant evaluations for soilborne pest and Cyperus rotundus control in fresh market tomato. Crop Protection. 23:889-893.
  • Hartz, T.K. et al. 2005. Mustard cover crops are ineffective in suppressing soilborne diseases or improving processing tomato yield. HortScience. 40:2016-2019.
  • Locascio et al., 1997. Fumigant alternatives to methyl bromide for polyethylene-mulched tomato. HortScience. 32:1208-1211.
  • McGovern, R. J. et al. 1998. Evaluation of application methods of metam sodium for management of Fusarium crown and root rot in tomato in southwest Florida. Plant Dis. 82:919-923.
  • Sydorovych, O. et al. 2008. Economic evaluations of methyl bromide alternatives for the production of tomatoes in North Carolina. HortTechnology. 18:705-713.