Ginseng and Other Medicinal Plants Part 6

If examined early in the morning the diseased spots are of a darker green color and watery as if scalded. They dry rapidly, becoming papery and of a light brown color, definite in outline and very brittle. With the return of moist conditions at night the disease spreads from the margin of the spot into the healthy tissue. The disease progresses rapidly so that in a very few days the entire leaf succ.u.mbs, wilts and hangs limp from the stalk. If the weather is wet, the progress of the disease is often astonis.h.i.+ng, an entire garden going down in a day or two. Under such conditions the leaves may show few or no spots becoming thruout of a dark watery green and drooping as if dashed with scalding water. All parts of the top may be affected. The disease never reaches the roots, affecting them only indirectly.

Cause of the Disease.

The disease is the result of the growth of a parasitic fungus in the tissues of the Ginseng. This fungus is an Alternaria (species not yet determined) as is at once evident from an examination of its spores.

These are in size and form much like those of the early Blight Alternaria of Potato. These spores falling upon any part of the plant above the ground will, if moisture be present, germinate very quickly, sending out germ tubes which pierce the epidermis of the host. These mycelium threads ramify thru the tissues of the leaf or stem as the case may be, causing death of the cells. From the mycelium that lies near or on the surface arise cl.u.s.ters or short brown stalks or conidioph.o.r.es on the apex of which the spores are borne in short chains. The spores mature quickly and are scattered to healthy plants, resulting in new infections. Only one form of spores, the conidial, is at present known.

That the Alternaria is a true parasite and the cause of the disease there can be no doubt. The fungus is constantly a.s.sociated with the disease. Inoculation experiments carried on in the botanical laboratory this summer show conclusively that the germ tube of the spore can penetrate the epidermis of healthy Ginseng leaves and stems and by its growth in such healthy tissue cause the characteristic spots of the disease. This is of special interest as it adds another to the list of parasitic species of genus long supposed to contain only saprophytes.

Upon the general appearance of so destructive a disease, one of the first questions of the growers was "where did it come from?"

Believing that it was a natural enemy of the wild plant, now grown over powerful under conditions highly unnatural to Ginseng, I undertook to find proof of my theory. I visited a wooded hillside where wild Ginseng was still known to exist. After half a day's diligent search I obtained seventeen plants of different ages, one of which showed spots of the Blight. Examination with the microscope showed mycelium and spores of the Alternaria. Unfortunately I did not get pure cultures of the fungus from this plant and so could not by cross inoculations demonstrate absolutely the ident.i.ty of the Alternaria on the wild plant with that of the cultivated. So far, however, as character of the spots on the leaves, size and form of the spores are concerned, they are the same. This, I believe, answers the question of the source of the disease. Introduced into gardens on wild plants brought from the woods, it has spread rapidly under conditions most favorable to its development; namely, those pointed out in the earlier part of this paper.

The wind, I believe, is chiefly responsible for the dissemination of the spores which are very small and light. Not only does the wind carry the spores from plant to plant thruout the garden, but no doubt frequently carries them for longer distances to gardens near by. The spores are produced most abundantly under conditions favorable to such dissemination. During moist, cloudy weather the energies of the fungus are devoted to vegetative growth, the spreading of the mycelium in the host tissues. With the advent of bright sunny days and dry weather mycelium growth is checked and spore formation goes on rapidly. These spores are distributed when dry and retain their vitality for a long period. Spores from dried specimens in the laboratory have been found to germinate after several months when placed in water. The disease might also be very readily carried by spores clinging to the roots or seeds, or possibly even by the mycelium in the seeds themselves. The fungus very probably winters in the old leaves and stems or in the mulch, living as a saprophyte and producing early in the spring a crop of spores from which the first infections occur.

Summer History of the Disease.

Altho it is on the foliage that the disease first attracts the attention of the grower, it is not here that it really makes its first appearance in the spring. The stem is the first part of the plant to come thru the soil and it is the stem that is first affected. The disease begins to show on the stems very shortly after they are thru the soil, evident first as a rusty, yellow spot usually a short distance above the surface of the soil or mulch. The spot rapidly increases in size, becomes brown and finally nearly black from the mult.i.tude of spores produced on its surface. The tissue of the stem at the point of attack is killed and shrinks, making a canker or rotten strip up the side of the stem. Such stems show well developed leaves and blossom heads giving no evidence of the disease beneath. Occasionally, however, the fungus weakens the stem so that it breaks over. Growers have occasionally observed this "stem rot"

but have never connected it with the disease on the leaves later in the season.

[Ill.u.s.tration: Broken--"Stem Rot."]

It is from the spores produced on these cankers on the stem that the leaves become infected. The disease begins to appear on the leaves some time in July and by the middle of August there is usually little foliage alive. Infection frequently occurs at the point where the five leaflets are attached to the common petiole. The short leaf stems are killed causing the otherwise healthy leaflets to droop and wilt. This manifestation of the disease has not generally been attributed to the Alternaria. The seedlings are frequently affected in the same way causing what is sometimes known as the "top blight of seedlings."

From the diseased leaves and stems the spores of the fungus find their way to the seed heads which at this time are rapidly filling out by the growth of the berries. The compact seed heads readily retain moisture, furnis.h.i.+ng most favorable conditions for the germination of any spores that find their way into the center of the head. That this is the usual course of seed head infection is shown by the fact that it is the base of the berry on which the spots start. These spots, of a rusty yellow color, gradually spread all over the seed which finally becomes shriveled and of a dark brown or black color. Spores in abundance are formed on the diseased berries.

Affected berries "sh.e.l.l" from the head at the slightest touch. This manifestation of the disease has long been known as "seed blast." If the berries have begun to color the injury from the disease will probably be very slight. The "blasting" of the green berries, however, will undoubtedly reduce or destroy the vitality of the seed.

There is a strong probability that the fungus may be carried over in or on the seed.

[Ill.u.s.tration: End Root Rot of Seedlings.]

The roots are only indirectly affected by this disease. The fungus never penetrates to them. Roots from diseased tops will grow perfectly normal and healthy plants the following season. It is in the leaves of the plant that practically all of the substance of the root is made. The bulk of this substance is starch. The destruction of the foliage, the manufacturing part of the plant, long before it would normally die means of course some reduction in the growth and starch content of the root. However, it seems probable that the greater portion of root growth is made before the blight attacks the foliage. This seems borne out by the fact that even blighted seedlings usually show nearly as good growth and bud development as those not blighted. In the case of older plants this is probably much more true as the latter part of the season is devoted largely to growing and maturing the berries. The Alternaria blight is dreaded chiefly because of its destructive effects on the seed crop.

Preventive.

The first experimental work on the control of this disease so far as I know, was carried out by Dr. I. C. Curtis of Fulton, N. Y. Having suffered the total loss of foliage and seed crop during the season of 1904, Dr. Curtis determined to test the efficacy of the Bordeaux mixture the following season as a preventive of the blight. The success of his work, together with this method of making and applying the mixture is given by him in Special Crops for January, 1906.

Extensive experiments in spraying were carried out during the past season by the Ginseng Company at Rose Hill, N. Y., under the direction of the writer. During 1905 their entire seed crop was completely destroyed by the blight. Losses from the same disease the previous season had been very heavy. During 1905 they had succeeded in saving a very large proportion of their seedlings by spraying them with the Bordeaux mixture. Encouraged by this they began spraying early in the spring of 1906, just when the plant began to come thru the ground. This was repeated nearly every week during the season, the entire ten acres being sprayed each time. On account of poor equipment the earlier sprayings were not as thoroughly done as they should have been, and some disease appeared on the stalks here and there thruout the gardens. A new pump and nozzles were soon installed and all parts of the plant completely covered. Practically no blight ever appeared on the foliage. There was some loss from "blast of seed heads" due to a failure to spray the seed heads thoroughly while they were filling out. The seed heads Were doubtless infected from the diseased stalks that had not been removed from the garden. A very large seed crop was harvested. The formula of the Bordeaux used at Rose Hill was about 4-6-40, to each one hundred gallons of which was added a "sticker" made as follows:

Two pounds resin.

One pound sal soda (Crystals).

One gallon water.

Boiled together in an iron kettle until of a clear brown color. It is probable that more applications of Bordeaux were given than was necessary, especially during the middle part of the season when little new growth was being made.

From these experiments it is evident that the problem of the control of the Alternaria Blight of Ginseng has been solved. Thorough spraying with Bordeaux mixture begun when the plants first come thru the ground and repeated often enough to keep all new growths covered, will insure immunity from the blight. Thoroughness is the chief factor in the success of this treatment. It is, however, useless to begin spraying after the disease has begun to appear on the foliage.

_To the President and Members of the Missouri State Ginseng Growers'

a.s.sociation._

Gentlemen--In response to a request from your secretary, I was sent early in August to investigate your Ginseng gardens, and, if possible, to give some help in checking a destructive disease which had recently appeared and had in a short time ruined much of the crop. Thru the aid of some of your a.s.sociation, at the time of my visit to Houston, and since that time, I have been furnished with valuable data and specimens of diseased plants.

The summer of 1904 was marked by a very abundant rainfall. The shade of the arbors kept the soil beneath them moist, if not wet, for several weeks at a time. This moist soil, rich in humus and other organic substances, formed an exceedingly favorable place for the growth of fungi. Gardens under dense shade with poor drainage, suffered the greatest loss. All ages of plants were attacked and seemed to suffer alike, if the conditions were favorable for the growth of fungi.

Symptoms of Disease and Nature of the Injury.

Between the first and the fifteenth of May black spots having the appearance of scars appeared on the stems of the Ginseng plants. All ages of plants were attacked. The scars increased in number and grew in size, sometimes encircling the stem.

The first indication of injury was seen when one leaflet after another turned brown; from them the disease spread down the petiole to the main stalk. Other stalks were attacked so badly that they broke off and fell over before the upper portions had even become withered. After the loss of the top from this disease the crown of the root was liable to be attacked by fungi or bacteria, causing decay. I found little of this in the gardens at Houston. The greatest loss caused by this disease lies in the destruction of the seed crop.

I have succeeded in isolating and studying the fungus which causes this disease. The fungus belongs to the genus Vermicularia and occurs on a number of our common herbaceous plants. I found it near Columbia this autumn on the Indian turnip. The fungus lives beneath the epidermis of the Ginseng plant; breaking the epidermis to form the black scars in which the spores, or reproductive bodies, are produced. The spores when ripe are capable of germinating and infecting other plants.

Treatment.

Fortunately this disease can be effectually checked by the use of Bordeaux spraying mixture.

Damping-off Disease.

Another source of loss was in the damping-off of young plants. The fungus which causes this disease lives in the surface layer of the soil and girdles the plants at the surface layer of the ground, causing them to wilt and fall over. The trouble can be largely avoided by proper drainage and stirring the surface layer, thus aerating and drying the soil.

The Wilt Disease.

By far the most destructive and dangerous disease remains to be described. It made its appearance about the first week in July, causing the leaves to turn yellow and dry up; the seed stem and berries also dried up and died before reaching maturity. This was the disease which caused the greatest loss; whole plantations often being destroyed in a week. Neither the Bordeaux spraying mixture nor lime dust seemed to check its ravages.

I have succeeded in isolating the fungus which is the cause of this destructive disease and have grown it in the laboratory in pure cultures for nearly five months. Cultures were made by sc.r.a.ping the dark spots on diseased stems with a sterile needle and inoculating sterilized bean pods or plugs of potato with the spores sc.r.a.ped from the stem. In two or three days a white, fluffy growth appears on the bean pod which rapidly spreads until it is covered with a growth which resembles a luxuriant mould. I have also isolated this fungus and made cultures from the soil taken from diseased beds.

The fungus belongs to the genus Fusarium and is probably identical with the fungus which is so destructive in causing the wilt of cotton, watermelon and cowpeas, and which has been carefully studied by Smith and Orton of the United States Department of Agriculture.

Treatment.

It will be seen from this brief description of the fungus that it is an exceedingly difficult disease to combat. Living from year to year in the soil it enters the plants thru the roots and spreads upward thru the water-conducting channels. It does not once appear on the surface until the plant is beyond recovery. Obviously we cannot apply any substance to kill the fungus without first killing the plant it infests.

There is but one conclusion to be drawn, viz.: That application of fungicides will not prevent the wilt disease.

There are, however, two methods of procedure in combating the disease: First, the use of precautions against allowing the fungus to get started; second, the selection and breeding of varieties which will withstand the disease.

From the very first the arbor should be kept free from all possible infection by the wilt fungus.

Gardens should be small and located some little distance apart, then if one becomes infected with the disease it can be taken up before the disease infests a larger territory. If the roots have reached merchantable size they had best be dried and sold, since they are likely to carry the disease when transplanted. If they are transplanted they should be carefully cleaned and reset without bruising.

Proper drainage is very necessary for a successful Ginseng garden. It is advisable to locate the garden on a gentle slope if possible. In all cases the ground should be well drained.

The belief of many that the death of the Ginseng was due to the wet season was without foundation, because the fungus develops best in soil which is continually moist and shady. This also accounts for the well-known fact that all rots, mildews and rusts are worse in a rainy season than in a dry one.

[Ill.u.s.tration: The Beginning of Soft Rot.]

Ample ventilation must also be provided in building the arbor. Many arbors are enclosed at the sides too tightly.

The material used for mulching should be of a sort which will not contaminate the garden with disease. Some fungi will be killed if the ground is allowed to freeze before putting on the mulch.