By Sean Westerveld and Melanie Filotas, OMAFRA
A trial was established in 2011 in a commercial ginseng field to examine the impact of different types of straw on ginseng growth and susceptibility to pests. Rye and wheat are considered to be allelopathic on some plant species, which means they emit chemicals that restrict the growth of susceptible plants. Preliminary studies in the past have suggested that under certain conditions, rye straw or the volunteer rye plants may cause damage to ginseng roots. We also wanted to determine if these straws or volunteer grains may influence pest populations in the soil, either by introducing pests to the field, or by promoting their growth.
We tested four treatments:
- Rye straw with the volunteer rye allowed to grow until April of 2012, when it was killed off by a glyphosate application (Figure 1).
- Oat straw with the volunteer oat allowed to grow for the fall of 2012, which then died over winter.
- Wheat straw with the volunteer wheat allowed to grow until April of 2012, when it was killed off by a glyphosate application.
- Wheat straw with the volunteer wheat killed off shortly after emerging in the fall of 2012.
Figure 1. Volunteer rye in ginseng killed off by a glyphosate application in April 2012.
Note: Glyphosate application is not permitted in the fall because evidence suggests that it can damage the ginseng as it emerges the following spring. This treatment could be replaced by a Venture application in the fall, following by a glyphosate application in the spring before ginseng emergence.
Ginseng was allowed to grow under standard commercial practices for the summer of 2012 and assessed for yield and damage on September 19, 2012.
Table 1. Effect of type of straw and volunteer grain on ginseng seedling root health after one year of growth.
| Straw | Volunteer Grain | Total root weight (g/m2) | Weight of undamaged roots (g/m2) | Percent Undamaged | Percent with root constrictions |
| Rye | Rye | 60.5 az | 22.7 a | 39 a | 42 ab |
| Oat | Oat | 73.4 a | 23.3 ab | 30 a | 59 a |
| Wheat | Wheat | 84.2 a | 31.8 ab | 36 a | 54 a |
| Wheat | None | 94.2 a | 48.5 b | 54 b | 29 b |
z Numbers in a column followed by the same letter are not significantly different at P=0.5, Fisher’s Protected LSD Test.
The results do not show any significant allelopathic effects of wheat or rye on ginseng growth. While the rye treatment had the lowest total root weight, there were no significant differences among the treatments. The primary symptom of pest damage in the trial was root constrictions (Figure 2), which also occurred in our fumigation and cover crop trial last year. Root lesion nematodes have been confirmed as the cause of these symptoms based on pot experiments conducted over the summer. The results show that the wheat straw treatment with the volunteer wheat killed off in the fall had significantly lower damage from root lesion nematode than the three treatments in which the volunteer grain was allowed to grow. While total root weight was not significantly different among the treatments, it was numerically highest in the wheat with no volunteer wheat treatment. There were no differences among oat, wheat and rye straw in damage to nematodes or any other pests.
Figure 2. The most common symptom of pests in the trial was root constrictions caused by root lesion nematodes.
Rye, wheat and oat are all susceptible to root lesion nematode. The results of our trial last year confirmed that fumigation by Telone, the fumigant used in the current trial as well, is not 100% effective in controlling nematodes. Any nematodes that remain in the soil will be seeking a host plant to feed on over the fall. All three of these crops may serve as a host, along with any susceptible weeds that emerge over the fall. When the wheat was killed off shortly after emergence, it is possible that the root lesion nematodes died off. In the other three treatments, the nematodes could have survived and even multiplied during the fall, and emerged the following spring to damage the germinating ginseng.
The results of the trial are preliminary and more data analysis is required. In addition, it is not known if the roots will eventually grow out of the nematode damage. We have to continue to track the results for another two years. However, the results suggest that killing off the volunteer grain in the fall soon after they sprout, may reduce nematode damage to the ginseng. It is not known if this could have other implications, such as causing more straw erosion over the winter or increasing frost and freeze damage.
