Chapter 12: Foliar, seedling, and root disorders

In Chapter 11: Overview of Disease Management reviewed cultural methods for preventing diseases from occurring in the garden. It also discussed industry contacts that Northwest growers can turn to for accurate disease diagnosis and management.

In this chapter we shall review the different classes of ginseng pathogens and review how to identify them and control them with suitable fungicides.

Ginseng pathogens can be grouped into 3 categories. The following table provides an over view of the foliar, seedling, and root rot pathogens that reduce productivity of North American ginseng.

Foliar pathogens	Seedling pathogens	Root rot pathogens
Botrytis cinerea, Alternaria panax, Phytophthora cactorum	Rhizoctonja solani, Fusarium sp., Pythium sp.	Phytophthora cactorum, Cylindrocarpon sp.

Above ground foliar leaf blights can be attributable to Botrytis, Alternaria, and occasionally Phytophthora (Phytophthora cactorum). Seedling pathogens that contribute to damping off include Pythium, Rhizoaania, and Fusarium. Below ground root rot is generally attributable to either Phytophthora, or Cylindrocarpon. Accurate diagnosis and management depends upon growers carefully reviewing the signs, predisposing factors, and chemical alternatives inherent to each category.

Foliar diseases
Growers will generally find foliar leaf disorders don't show up until the leaves are fully developed. During garden walking, individual plants will be noted, as opposed to large blocks. The plants that are most susceptible are the ones that are growing together densely.

Botrytis blight
Of the foliar disorders affecting ginseng in areas west of the Cascades, Botrytis leaf blight (Botrytis cinerea) is the most common. The cool, cloudy weather, with abundant spring rainfall, sets the ideal conditions for pathogen spread. Botrytis has a long history of causing crop losses in red raspberries, blackberries, strawberries, greenhouse bedding plants, and flowers. Botrytis cinerea overwinters in the debris and surrounding vegetation near the ginseng garden. In the spring the fungus begins to grow and release spores knows as conidia, which can be carried by the wind and rain to infect developing eaves, and occasionally flowers.

The characteristic symptoms on leaves include water soaked, concentric lesions, which start at the leaf tips and proceed back along the leaf mid rib (see Fig. 1). Unlike Alternafia or Phytophthora, the plants do not wilt. Where plant growth is dense, the pathogen can easily spread from one plant to the next. With advanced decay, the leaves can shrivel (see Fig.2), as with Phytophthora leaf blight. If the roots are examined, they will appear normal.

The best way to reduce Botrytis infections ftom beginning is to ensure that the garden receives sufficient air movement, to dry the foliage during the day. Seeding rates should be reduced in new beds to reduce plant density. Gardens established by transplants have considerably less infection, as there is more air movement between the plants.

The fungicide Rovral is efficacious against Booyfis if applied early when the plants are first emerging. The Rovral label lists Alternaria panax, and not Botrytis cinerea. Northwest berry growers have found that Rovral does very well on Botrytis flower blight, and fruit rot. Note though, that they are concerned about developing resistant strains of Botrytis and therefore tank mix Rovral with Captan (Captan is not registered on ginseng). Wisconsin growers have already seen resistance to Rovral in their battle with Alternaria blight. Northwest growers will need to be sure that that don't develop resistant isolates of Botrytis with continual use of Rovral

Botrytis fungicide	Application notes
Rovral 4F (flowable iprodione), Rhone Poulenc Ag Company	Apply as a foliar spray using 1.5 to 2.0 pints per acre. Make the first application when conditions become favorable for disease development. Use sufficient water (10 gallons at least) to attain thorough coverage. Do not apply more than 5 times per season. Do not apply within 36 days of harvest. When used with in an Alternating Program with copper hydroxide products (Kocide or Champion) apply 1.0 to 1.5 lbs./ac Rovral on a 14 day basis when used with copper hydroxide
Rovral 50 SP (soluble packets)	Apply 2 packets per acre; follow remaining directions as above. When alternated with copper hydroxide, use only one 1 packet per spray tank

Alternaria leaf and stem blight
Alternaria blight caused by Alternaria panax, is the most common disease of ginseng throughout the world. It has been isolated in ginseng growing in eastern Washington, but not in areas west of the Cascades. Alternaria blight is exacerbated by high humidity during the summer growing season and thus is a major problem in Wisconsin and Ontario. The low relative humidity during the summer months in western Washington and Oregon plays a major role in preventing this major disease from beginning. In British Columbia the need for summer irrigation leads to a flare up of this disease. BC growers also know that Alternaria can survive very well in the straw mulch that is applied to the gardens.

The fungus attacks all parts of the ginseng plant. Leaves will show circular light brown lesions surrounded by yellow hallow (see Fig. 3). During humid or wet weather, the lesions will become darker, while in dry weather they become papery dry (see Fig. 4), and may fall out. The yellow halo helps distinguish this pathogen from either Botrytis or Phytophthora leaf blight. Leaf stock stems will display lesions 1/4" to 2" long (see Fig. 5). With further development, the lesion develops into velvety mat of dark spores. Finally, as the lesions circle the stems, the leaf stalks collapse and the foliage dies.

Chemical control involves the use of tank mixes of copper compounds (Kocide, Champion) and Rovral. Fungi including Botrytiss cinerea, can build up resistance to Rovral. Tank mixing with copper compounds helps reduce the threat of developing resistant isolates.

Alternaria fungicides	Application notes
Kocide DF, 61.4% copper hydroxide, Griffen Corporation Kocide DF, 61.4% copper hydroxide, Griffen Corporation	Use as a tank mixes with Rovral. Combine 2.6 pounds of Kocide or Champion with 2 lbs. of Rovral 5OW in 100 gallons of water. Apply in the spring at 7 day intervals until warm weather begins (generally first half of June). Apply at least 8 hours before an expected rain shower. Thorough coverage is very important. Alternana blight is worse in dense canopies of 2, 3, and 4 year old ginseng. Use of a spreader sticker is strongly advised to keep the copper on the plants.
Champion WP, 77% copper hydroxide, Agtrol Chemical Products	Same as above

Phytophthora leaf blight
The leaf blight phase of Phytophthora cactorum, is the foliar version of the disease that also attacks the roots. The leaf blight phase is not commonly seen. Lesions first to appear as green black wifted areas of the leaves. The leaf margins can become papery thin and transparent (See Figure 6). Plants infected wilt in clumps (see Figure 7), as associated with the loss of root
function.

Unlike Alternaria spores, which are carried by the wind, Phytophthora spores can only be transported by water. A driving rain can carry the spores (known as zoospores) up from the mulch onto the leaf tissue. Spores can also be carried by machinery moving through the field. The disease can spread from one plant to the next if the foliage stays wet for several hours.

Cultural control for this disease includes planting on raised beds to improve drainage, ensuring that the prevailing winds currents are not obstructed by vegetation, and limiting traffic through the beds when the foliage is still wet.

For chemical control Oregon and Washington growers can use the fungicide Alliette. This compound will help control both the foliar leaf blight phase of Phytophthora cactorum, as well as the root rot stage. It will also suppress Alternapia leaf blight.

Phytophthora leaf blight control	Application notes
Alliette WDG, (water dispersible granules), Fosetyl Al, Rhone Poulenc	Apply 5 lbs ./100 gallons of water in the spring when conditions become applications on 7 day intervals until warmer weather develops (mid-June west of the Cascades). Do not tank mix with copper compounds as leaf phytotoxicity can occur.
Alliette WSP (water soluble packets)	Apply 5.0 lbs./100 gallons of water (equal to 5 packets of product). Follow the remainder of the use precautions as above

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Seedling pathogens
There are a group of pathogens including Rhizoctonia solani, Fusarium sp., Pythium, and Phytophthora can cause a seedling disorder known as damping off in which first year plants collapse in the spring and soon die off.. Upon examination of the young plant, after it has been dug up, no root will be evident. Death occurs during the first 2 weeks of emergence of the garden.

Damping-off fungi are generally weak pathogens. While they are always present in the soil, their numbers are exacerbated under conditions of cool moist soil. Control of damping off begins in the spring, during the first few weeks of April, as the ginseng plants are first coming up. It is advisable to keep the shade panels furled for at least 2 weeks in order to allow the beds to warm up and dry out. Fears of sun damage are lessened at this time since the sun's rays are still quite weak.

Another important consideration is to ensure that a perched water table is not formed during the preparation months. If the ground is disced late in the summer, when soil moisture is lacking, a 'plow zone' will form which will impede soil moisture drainage to the lower depths of the soil. The only recourse on these soils with a 'hardpan layer' is to run a sub soiler through where the beds will be places. Soil texture has a key role here. Poorly draining sites will potentially suffer more damping off.

There are fungicides that will help fight against these pathogens. Ridomil 50W and Ridomil Gold EC, manufactured by Ciba Geigy Crop Protection, are both registered on ginseng. Ridomil should be applied in March, as the plants are starting to come out of dormancy, in order to protect the developing tissue.

Ciba also markets Apron 50W, which has the same active amount of metalaxyl, for use on ginseng seeds to help protect them against damping off .

Damping-off fungicides	Applicaton notes
Ridomil 5OW, metalaxyl, CIBA GEIGY	Apply either pre plant or post plant to help control damping off. Use 2 4 lbs./treated acre. Incorporate with irrigation (rainfall will substitute for irrigation).
Ridomil Gold EC	Apply 3/4 pint/acre in a drench with at least 100 gallons of water

See protectant fungicide	Application notes
Apron 50W	Apply .5 to 1. 0 ounces per 100 lbs. of seed prior to planting

Phytophthora root rot
The pathogen Phytophthora cactorum can lead to serious root rot on primarily 3 and 4 year old stands. This disease is all too common in poorly drained portions of the ginseng garden. The first sip of this disease is a cluster of wilting plants. When the roots are dug up for examination, they will have a beige interior, as opposed to a bright white color. The root will fell rubbery, as opposed to crisp. A field test to determine the presence of this disorder is to squeeze the suspect roots. Roots with a creamy consistency are clearly infected. There may be a pungent odor as well. While roots may appear normal at harvest, during the drying phase obvious gray black discolorations on the roots will be clearly evident.

Cultural prevention of root rot begins during the preparation months leading up to planting. Clearly, raised beds and excellent tilth are the keystones of prevention. Low areas of the field will either need to tiled (see Chapter 3: Site Preparation) or simply not planted to ginseng. Soil fumigation has not been found effective. Sanitation in existing fields is important. Diseased plants should be dug up and removed, as well as their neighbors within a 1 foot radius. Spray a 10% bleach/water solution onto boots, and shovels used to dig up the un healthy areas. Pressure wash the lugs of the tractor that traverses a rot infested area. Purchase seed from a grower that has had healthy ginseng plants.

For chemical control, both Ridomil 2E, and 5OW can be used as soil drenches as previously outlined for the prevention of damping off.

Rusty root
Rusty root is referred to as a form of root rot where small, raised, reddish brown areas (see Figure 8) appear on the surface of harvested roots. These scaly lesions are generally only on the surface of the root. The above ground leaves and stems generally look fine. In the Northwest rusty root first shows up on 2 year plants, on the shoulder or upper portions of the roots. In 3 and 4 year old plants it spreads further down the length of the root.

There has not been a definitive answer to the causes of rusty root. The pathogens Cylindrocarpon and Fusarium may be responsible. Plant nutrition may play a part as well. One consolation: during the drying phase, many of the rusty lesions seem to dry out leaving the dried root perhaps marketable. Certainly any rusty roots can be dried and used for capsules and powdered products.

Organic ginseng production
There are growers trying to produce organic ginseng in western Washington. In order to prevent excessive disease development in their gardens they have situated their beds on sandy ground of excellent tilth. Lime sulfur, and Bordeaux mixture, can be used to reduce the incidence of Botrytis leaf blight. As for market prices, fresh root may return $20/lb. In order to become certified organic, growers will need to contact the Washington State Department of Agriculture in Olympia, WA. Contact Miles McEvoy, at 360/ 902-1924 for further information.