Ginseng Gnawing 101 - Cut Stems and the Creatures that Cause Them

Late spring is the time of year when ginseng growers and garden walkers start seeing evidence of seedlings that have been cut as they emerge through the straw. With cut stems we often think of cutworms, but there are actually a variety of creatures that can cause similar symptoms in ginseng. Here's a quick review of each and how to distinguish between them.

Cutworms are perhaps most commonly associated with cut stems. Cutworms are the immature stages of a family of night-flying moths called noctuids. Cutworms are variable in appearance but are usually dull grey to brown with darker markings, and are often hairless and greasy looking. They tend to curl into a "C" when disturbed. Cutworms spend their days in soil, emerging in the evening to feed on stems (and sometimes leaves) of ginseng crops. Cutworm damage can be distinguished by their habit of severing plant stems like a knife (Figure 1). The upper portion of the stem falls over and is often distinguishable by the severed leaves lying upside-down on the straw.

Slugs are soft-bodied, slimy animals (essentially snails without a shell) which are more closely related to clams than insects. They move relatively slowly and as they move they secrete a layer of mucus, called a "slime trail". They prefer cool, wet areas (such as under straw mulch) and are most active at night. In older gardens, slugs will chew holes in leaves, berries and taproots. Cut stems are typically seen in seedling gardens. Unlike cutworms, which chew directly through the stem, slugs chew vertical holes in the side of the stem (Figure 2). Seedlings will not be completely severed, but rather bent over. Additionally, you may see evidence of a slime trail near feeding sites.

Mice will also chew on stems and exposed roots of ginseng. With mice, you often see elongated areas of chewing along the length of the stem (Figure 3), and like cutworms they can sever the stem. If you suspect mice, look for tunnelling beneath the straw, which is characteristic of mice as they move along the length of the beds.

Millipedes are only sporadic pests in ginseng, however on occasion they will attack seeds and emerging seedlings. Millipedes have elongated, hard bodies and range in colour from white to grey-black. They tend to coil up when disturbed, and can be distinguished from the other insects described here by their many legs, which run down the length of their body (typically there are two pairs for each body segment). As seedlings begin to extend above the straw, millipedes will chew them off where they break through the soil. Millipedes will chew anything that emerges, and not just the stem, so you will see a wider range of damage than with the other pests described (Figure 4).

No discussion of feeding on ginseng stems would be complete without mentioning grubs! Grubs do not technically cut stems, however they do feed on young ginseng roots in seedling gardens. Grubs in ginseng are usually the immature stage of the European chafer, a common beetle pest of turf and other crops in Ontario. Grubs have six legs with a C-shaped white body, dark head and darkened tail end. As they feed, the young plant is drawn down into the straw, so in contrast to cutworms the upper part of the plant is not left above the straw (Figure 5). Damage is most commonly seen in 2 year old gardens as circular empty spaces in beds, however at this point the grubs are typically not present in the garden.

Ginseng growers are most commonly focused on disease, however seedlings are also susceptible to damage by a variety of animal pests. When you see evidence of damage, it is important to properly identify the culprit, because control measures will vary with each one. For information on control options, refer to OMAFRA Publication 610, Production Recommendations for Ginseng.

Figure 1 - Typical cutworm damage on a ginseng seedling. Note that the top of the plant has been cleanly cut and is lying beside the stem.

Figure 2 - Slug damage to ginseng seedlings. Note that the stem has only been partially chewed and not completely severed (as with cutworms).

Figure 3 - Mouse damage to ginseng stem. Note the severed stems with long, elongated areas of chewing.

Figure 4 - Millipede damage to ginseng seedlings.

Figure 5 - This seedling has been pulled into the straw by grubs.

Related Links:

• Publication 610, Production Recommendations for Ginseng