The loss of the industry standard fumigant Telone C-17 (dcp+chloro) in 2011 left growers uncertain of how well the alternatives would work for the control of soil-borne nematodes and fungi in ginseng. In 2010 a trial was established in a commercial ginseng field to compare the alternative fumigants metam-sodium (as Busan 1236) and chloropicrin (as Pic-Plus) to dcp+chloro. The fumigants were applied under ideal conditions according to the label. This included irrigation ahead of time to ensure good soil moisture, rolling or packing immediately behind the fumigator and a small amount of irrigation afterwards to ensure a good seal of the soil surface. This trial pre-dated the requirements for tarping of chloropicrin, which is now required for all broadcast applications.

A seedling assessment conducted at the end of the 2011 growing season showed considerable damage from root lesion nematodes (Pratylenchus penetrans). The nematodes caused constrictions along the taproot containing rust-coloured vertical lines (Fig. 1). Metam-sodium plots had the least damage from root lesion nematodes at the time, while chloropicrin and dcp+chloro provided intermediate control, significantly higher than the unfumigated plots but lower than metam-sodium. As a result, total yield of seedling roots was also maximized by metam-sodium.

Figure 1. Constrictions on a ginseng seedling root caused by root lesion nematode feeding.

Final berry and root yield results from the end of the 2013 growing season are presented in Table 1. Due to high variability in the plot, there were few statistically significant differences among the treatments. Marketable yield was consistent for all three fumigants. While they were numerically higher than the unfumigated control, there were no statistically significant differences. Similar results were shown for total root yield, berry yield and weight per root. A higher proportion of the roots were pencil shaped in metam-sodium treated plots (Table 1), probably due to less nematode damage in the seedling year.

Table 6. Effect of fumigation on total and red (ripe) berry yield, total and marketable root yield, weight per root and percent pencil shaped roots at final harvest in August, 2013.

^z 1,3-dichloropropene + chloropicrin.
^y Numbers in a column followed by the same letter are not significantly different. NS = not significant.

The root lesion nematode damage identified in the seedling year was still present on the roots. However, there did not appear to be any new damage, suggesting that root lesion nematodes may only damage roots in the seedling year when they have no alternative hosts in the field. The roots had grown out of the constrictions, leaving only the rust-coloured vertical lines, which were stretched out as the root grew (Fig. 2). Other rusty root symptoms were also present on the root, likely the result of fungal pathogens. Fusarium was the primary fungus isolated from roots with rusty root symptoms, and has been identified as a cause of rusty root in previous research. This damage was more prevalent in one area of the field where root lesion nematode damage in the seedling year was less severe. Observations in the different areas of the trial suggest that metam-sodium had higher yield in areas where root lesion nematode damage was most prevalent, while chloropicrin and dcp+chloro had higher yield in areas with more fungal disease. This could suggest that the two alternative fumigants have different effects on the two main pathogen types, but further research is required.

Figure 2. By the third year, the former constrictions are no longer present, but vertical rust-coloured lines remain (just below crown) or the root forks (lower portion).

The results of this study suggest that the alternative fumigants can provide comparable control of nematodes and soil-borne pathogens to dcp+chloro when applied properly with good soil moisture and a good seal of the soil surface. However, the choice of the alternative product may depend on what pathogens are present in the soil at the time of fumigation. Additional research into biofumigants and the effects of tarping on the efficacy of fumigants is continuing.

This project was funded by a Farm Innovation Program grant to the Ontario Ginseng Growers Association. It was a collaborative effort between Dr. Sean Westerveld and Dr. Melanie Filotas, OMAF and MRA; Carl Atkinson, C&R Atkinson Farms Ltd.; and Dr. Catarina Saude, University of Guelph.