Dealing with Frost Damage in Ginseng

Frost damage has occurred in many areas of gardens across the ginseng growing area. The full extent of the damage and the potential for older plants to recover from the damage will not be known for a few days. At this time, it is critical that gardens containing frost damage are sprayed with protectant fungicides for both Alternaria and Botrytis. Alternaria is already showing up within the canopy (Figure 1) and Botrytis will grow on any damaged tissues in this humid weather. Botrytis spores are virtually everywhere in and around a garden, so disease can show up rapidly throughout a garden. Both Alternaria and Botrytis are relatively weak pathogens that will be much worse when the plant is weakened. It is important to avoid overhead irrigation under these conditions to reduce foliar disease issues. Moderate drip irrigation on the other hand can keep the plants as healthy as possible without promoting additional disease.

Figure 1. Alternaria lesion on a 4-yr old stem.

Seedlings with frost damage usually do not recover. Affected seedlings collapse on the straw and usually quickly turn papery and brown (Figure 2). Other seedlings are still standing erect but with a weakened, droopy appearance (Figure 3). Seedlings that emerged first and were closer to full expansion had less damage than newly emerged plants.  Some seeds are still emerging through the straw, so it best to wait until these emerge before making decisions on whether to continue to maintain the crop or to reseed.

Figure 2. Seedlings collapsed onto the straw as a result of frost.

Figure 3. Weakened seedlings still standing several days after the frost. It is unknown how well these will recover.

2-yr old plants also have major damage in some areas. Normally frost damage causes kinking of the stem above the straw, and plants can somewhat recover by turning back upwards towards the light. In some areas, such as one of our research plots, the plants are turning brown and will not recover (Figure 4). After a few days it will become apparent whether any plants will recover from this damage. If plants do not recover, it may be worth it to remove the shade in the worst areas to kill off any remaining plants that may linger and harbour disease. This would avoid having to apply pesticides for foliar disease, slugs and insects all season, although fungicides for root disease would need to continue. 2-yr old plants with top growth killed will come back from a secondary bud next year, but will likely be smaller than they would have been this year because of the extra energy required to produce another top.

Figure 4. 2-yr old research plot severely damaged by frost.

Older gardens have extensive kinking in some areas (Figure 5). Many of these will likely turn towards the light, but the canopy will appear twisted and uneven. Plants with kinked stems will not have the same yield increase this year as healthy plants. The biggest risk to these plants is foliar diseases within the twisted canopy that could destroy the canopy if protectant fungicides are not applied. While the canopy architecture has changed significantly, the same sprayer settings/nozzles should still work because the canopy is now more open and will allow fungicides to penetrate into the interior. Drop arms should still be used to get penetration of the canopy from the side. It is best to check the effectiveness of any spray with water sensitive papers placed in different areas of the canopy, and monitor the crop carefully to ensure disease is not spreading.

Figure 5. 3-yr old ginseng with extensive kinking.

In gardens intended for seed production, the developing seed head is often killed if the stems have kinked. The seed heads can remain green but will not develop or will quickly turn brown (Figure 6).

Figure 6. A seed head on a frost damaged plant. This will likely not develop due to the stem damage.

About Sean Westerveld

Ginseng and Medicinal Herbs Specialist, OMAFRA
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