Chapter 13: Insect management

In relation to other vegetable root crops, such as carrots and potatoes, cultivated ginseng has very few insect pests. None of the pests reviewed below contribute to any significant damage in ginseng gardens.

Slugs
Cultivated ginseng is highly susceptible to slug damage in the spring, as the weather stays cool and damp. The characteristic ragged holes in the leaves (see Figure 1) and the trails of mucus are the characteristic signs of slug feeding. Slug damage does not however appear on the roots below the soil surface. A moderate amount of slug feeding on developing leaves probably has very little effect on eventual root yield. Most slug feeding occurs at night; finding them during the day is difficult.

The Pacific Northwest is home to a great number of different slug species. Some of the more common include the small gray garden slug (Agriolimax reticulatus, see Figure 2, with permission from Ohio State University), the large spotted garden slug (Limax maximus), and the black greenhouse slug (Milax gagates, see Figure 3, with permission from the University of Nebraska). All of these species thrive in areas of moist ground and low sunlight, exactly the conditions common to the ginseng garden in the months of April, May and June. When warmer weather returns, slugs stop their feeding frenzy.

Slugs are hermaphrodites, that is every one of them are capable of laying eggs. The small, round, pearl-like white eggs will be found in sheltered areas in the soil. Eggs can hatch within 2 weeks. The greatest egg laying activity occurs in late summer after the first fall rains. The gray garden slug will also lay eggs in the spring. Slugs can live for as many as 12 months.

Control
By using sawdust to mulch their ginseng beds Northwest growers have greatly reduced slug populations. The drying action of the sawdust repels the slugs from entering the garden. Where straw is used on ginseng, slug damage can become overwhelming. Woods cultivated ginseng is more prone to slug damage, as sawdust is often not used for mulch. Growers should delay pulling the shade panels over the beds in April to give the garden time to dry out. Keep the area surrounding the garden tilled or covered with sawdust to discourage slugs from crawling into the garden.

Bait can be used in ginseng gardens to attract and kill the feeding slugs. Metaldehyde, the specific chemical used in baits since the 1930’s, paralyzes slugs for about 48 hours. If conditions are moist however, up to 100% of the population has been found to revive and crawl off! Keep pets, and children out of the garden after slug bait applications. Some growers have tried covering the slug bait beneath small pieces of plywood, with one corner resting on a stone, to keep the bait drier and fresher.

Slug control product	Application notes
Deadline Bullets, containing 4% metaldehyde, manufactured by Pace International, 500 7th Ave. S, Kirkland WA, 206/ 827-8711	Broadcast 20 to 40 pounds over the top of the beds. Do not contaminate the ginseng roots. For best results apply in the evening. Especially beneficial, if applied following a rain shower. Baiting has been found to be considerably more effective in the fall to kill mature slugs and prevent them from laying eggs. Young slugs are harder to kill in the spring.

Wireworms
Of the most damaging soil-dwelling pests in Northwest agriculture wireworms are considered some of the worst as they feed on a wide variety of annual crops. The yellow-brown, shiny slender larvae (see Figure 4) of adult click beetles (see Figure 5) have been found feeding at the base of young ginseng leaf stalks. The most important species are the Pacific Coast wireworm (Limonius canus), and sugarbeet wireworm (L. californicus). Larvae mature in the soil, at a depth of from 12”-24”. They rise to the soil surface in the spring as the soil temperature increases rises above 50 F.

After pupation the adult click beetles continue to live in the soil. On seedlings, a close examination of the base of the leaf stalks will show a frayed, ragged section of the stem. With enough damage the leaf stalks have been found to collapse. Fortunately the damage has been spotty and limited. The wireworms will travel deeper into the soil when the soil temperatures rise during the summer.

In British Columbia the recommendation for ginseng growers is to determine the presence of wireworms during the preparation of ground prior to shaping beds for seeding. This is done by placing white cooking flour as a bait 4” into the soil with a small trowel. There should be 10 bait stations for each acre of ground, placed at random. If 2-3 wireworms are found feeding per bait station 4 days later, there may be reason to consider controlling the pests.

The only registered pesticide for this pest on ginseng is Diazinon. It has to be sprayed on the ground before planting and then tilled under in the top 4-8” of the soil.

Wireworm insecticide	Application notes
Diazinon 4 Spray, containing 48% diazinon, manufactured by Wilbur Ellis	Use 3-4 quarts per acre broadcast just before planting and incorporate into the top 4-8”. Use at least 10 gallons of water in the spray tank.

Nematodes
Two different species of soil nematodes should be considered for ginseng. The root-knot nematode (Meloidogyne hapla), and the root lesion nematode (Pratylenchus penetrans) have both been found in northwest ginseng gardens. Nematodes are microscopic worms that feed in or on the exterior of plant roots, leading to a reduction of plant vigor.

The previous crop before ginseng plays a role in nematode population dynamics. Alfalfa can serve as host for both root-knot, as well as root lesion nematodes. Grasses have been found to be a suitable host for root lesion nematodes. As ginseng stays in the ground for at least 4 years nematodes have a chance to increase their populations. The symptoms of root-knot nematode feeding on ginseng roots are the presence of enlarged, tumor like swelling on the fine root hairs (see Figure 6). Dr T. Vrain, nematologist (vraint@em.agr.ca), with Pacific Agri-Food in Summerland British Columbia reports that root lesion infestations can adversely affect cultivated ginseng.

Threshold levels for both species of nematodes have been set. If root lesion nematode populations exceed 100 per 100 cc of soil, when sampled in late summer, soil fumigation prior to planting is suggested. For root-knot nematodes, the population threshold is only 1 per 100 cc of soil.

In western Washington berry producers have had a considerable amount of experience dealing with root lesion nematodes. On this perennial crop high enough populations have been found to result in plant stunting. The highest population of lesion nematodes will be found in fields that were once planted to perennial horticultural crop as berries, orchard crops, or ornamentals. The best recommendation for horticultural crop producers is too collect soil samples in late summer for nematode testing. If the populations are high enough, soil fumigation is often recommended.

Potato growers have learned that if they grow a crop of either of oats (cultivar 'Saia') or cereal rye (cultivar 'Wheeler') for 2 years that will nearly eliminate root-knot nematodes and reduce root lesion populations significantly. Ginseng growers could take this finding and apply it to their gardens as well. As explained in Chapter 3: Site Preparation cereals sown before planting ginseng can help considerably to enrich the soil tilth.

If nematode levels are still fumigation can be considered. The fumigant Telone II is the most commonly used product for areas west of the Cascades. Fumigation with Telone II will cost approximately $500 per acre. Broadcast fumigation will control wireworms as well. It will not have any effect on soil pathogens or weed seeds.

Fumigant	Application notes
Telone II, containing 1,3-dichloropropene as the active ingredient, manufactured by DowElanco	Have Telone II custom applied pre-plant broadcast to weed, debris, and clod-free soil in early September by the use of injection equipment. Wait 2 weeks, or once the odor or the fumigant has dissipated, before seeding or planting a crop. Once ‘clean’, fumigated soil should not be re-contaminated with planting stock or soil from gardens known to have a history of nematodes.