Ginseng Crop Update – May 19, 2016

In most areas frost did not occur over the weekend. However, the cold weather itself may cause some minor damage to ginseng. In general, the stems will still be intact, but the leaves may be distorted or the tops may not fully extend. Until the tops fully expand, it is not known how permanent the damage will be.

Some older plants show leaves curled in toward the vein (Figure 1). In the past these symptoms have been attributed to either cold injury or glyphosate damage. It is possible that glyphosate applied this spring did not break down as fast as it normally does on the straw because of the cold weather and the plants were injured as they came through. This has been noted before for late fall applications. It is also possible that it is just cold injury affected a certain stage of plant development. It is unknown if these plants will recover and fully unfold.

160519 Figure 1
Figure 1. Patchy plants with curled leaves are showing up in several older gardens.

Most fields were covered with frost cloth, which would have moderated temperatures under the cover somewhat over the weekend.  However, high winds while the cloth was on the field caused some physical damage to leaves, especially where the cloth broke loose and flopped around over the canopy. There may also be some distortion caused by the cold spell in early April in areas where plants would have emerged from the soil below the straw at that time (e.g. south facing slopes, very sandy and dry areas).

All of this potential stress on the plants, along with higher humidity under the covers, could lead to an outbreak of both Botrytis and Alternaria as the temperature warms. The disease pressure will likely not be as severe as if a frost has occurred. However, a failure to catch initial infections now could lead to a major outbreak if warmer and more humid temperatures come next week. Apply a protective fungicide for both Alternaria and Botrytis as soon as possible after frost covers are removed. It is also important to scout fields regularly to ensure infections haven’t been missed by the fungicide applications.

Conditions have been too cool and dry for foliar Phytophthora to be an issue so far. That could easily change as soon as wetter weather occurs. Root infections of Phytophthora or other root diseases will likely be the cause of any wilting symptoms noted so far. During emergence, tops are highly susceptible to foliar Phytophthora, so it is important to ensure plants are protected before rainfall occurs, especially in gardens where root Phytophthora is known to be present.

About Sean Westerveld

Ginseng and Medicinal Herbs Specialist, OMAFRA
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