The figures may be considered average for the two areas. One important difference is the length of time the disease is likely to be active-57 days in Georgia and 36 in Maryland. Equally important is the fact that in Georgia the disease is active 5 weeks before the time the plants are half-grown, February 7 to March 15. In Maryland this critical period is only 2 weeks long, May 1 to May 15. Again, with a warm January in Georgia, plants come up early, and the blue mold may be observed as early as January 22. February weather in Georgia typically has many cool, foggy days, which favor the spread of blue mold. In Maryland the weather after blue mold appears is typically bright and clear. The differences explain why a disease with a destructive record in Georgia is only moderately troublesome in Maryland, although practically all beds in each State are infected each year,

Conditions in South Carolina approach those in Georgia. Tennessee, Kentucky, and Pennsylvania have conditions much like those in Maryland.

When blue mold became established in the flue-cured area in 1931, the disease had behind it a long history in Australia. Control was first attempted in the United States by spraying With bordeaux mixture. It failed. An extensive investigation of fungicides was made. An effective gas treatment was announced in 1935. Benzol was the material used. Benzol vapors held in by a heavy muslin cover were effective in Australia in preventing the disease and checking its development after infection had occurred.

A modification of the benzol gas treatment, worked out in this country, substituted paradichlorobenzene, a crystalline material. It was found that the crystals, scattered over the ordinary cotton used over tobacco beds and then covered with a heavy muslin, slowly vaporized. The vapors given off controlled the disease. Between 1.5 and 3 pounds of paradichlorobenzene are needed for 100 square yards, depending on whether the weather is cool or warm and on whether the cover is well above or down close to the plants.

A good practice is to wait until the disease is at hand and treat three successive nights the first week, and then twice a week. Five or seven treatments are usually enough for the season. Gas treatment is effective but laborious and expensive. It has been largely superseded by fungicidal sprays and dusts.

A combination of cuprous oxide and cottonseed oil makes a good spray. Its effectiveness is due to the protection it gives the leaf surface and its penetration into the leaf tissues. When the infection occurs, the size of the lesions is limited and the plant suffers only a slight attack.

The new carbamate materials, of which the first was Fermate-ferbam (ferric dimethyl dithiocarbamate), are effective against blue mold. Somewhat more effective is a similar material, Dithane Z-78; or Parzate; or zineb (zinc ethylene bisdithiocarbamate). They can be used as dusts or sprays equally effectively.

In areas where mold is very destructive, it is well to begin treatments when the plants are the size of a dime. Elsewhere treatments may be delayed until mold is first reported in the locality. The recommended rates for spraying are Fermate, 4 pounds to 100 gallons of water; Dithane Z-78 and Parzate, 3 pounds to 100 gallons. In mixing, the powder should be thoroughly worked into a little water before the bulk of the water is added. One should start applications in time, apply enough material so that the leaf surfaces are visibly coated, and make applications twice a week until the plants are in the field or mold has disappeared because of warm weather.

The usual schedule is two applications a week. Depending on the season and area, 7 to 12 applications will be needed. Spraying is usually done without removing the cotton covering from the bed. For 100 square yards when the plants are very small, about 3 gallons are needed; 5 or 6 gallons are needed when plants are half-grown. If mold appears in a bed that is being sprayed, the affected spots should be sprayed with a double-strength mixture for one or two applications, or the amount of spray mixture should be increased until the spread of the disease has been checked.

Failure to control blue mold with these methods very likely is due to too late a start (after the disease is spread throughout the bed) or an inadequate application that does not coat the leaves with the fungicide. During a wet period, instead of missing an application, as often happens, one should make an extra application.

The materials recommended for spraying are equally effective as dusts.

Satisfactory dust formulations are Fermate, 15 percent; and Dithane Z-78 or Parzate, 10 percent. Talc or Pyrax (pyrophyllite) are satisfactory diluents. Fuller's earth, clays, lime, and land plaster are undesirable.

Dusting should be done when there is no wind. Early morning usually is the best time. If beds are 4 yards wide or less and the cotton cover is at least 6 inches above the ground, the dust can be applied without removing the cotton. If the bed is wide and the cotton close to the plants, one should remove the cotton.

The amounts of dust needed for 100 square yards of bed are about 2 pounds an application when plants are small and about 3 pounds when they are half-grown or larger. As with spraying, if blue mold does appear in a bed that is being dusted, the affected area should be treated heavily until the disease is checked. The regular dust schedule is two times weekly, but the leaf surface must be kept visibly coated and the protective coating must be renewed after every rain. Occasionally, because of rains, three or four applications are required in a week. Usually the total number for the entire season is 7 to 15.

Dusting takes less time than spraying, and does away with the need for carrying water. Since it requires about twice as much material, and because dusts are bought ready-mixed, their cost is greater but growers generally regard the greater convenience of dusting as more than counterbalancing the increased cost.

BLACK SHANK can spread rapidly into new areas and is a serious threat where-ever it occurs.

It almost always appears first in a low place in a field. Usually about midsummer a few plants begin to wilt. If you pull one of these plants in the early stages of the disease and examine the roots, you will find that one or more of the large lateral roots is blackened and dead. At this early stage the stalk will be free from decay or discoloration. As the disease progresses, the entire root system and the base of the stalk decay, and the plant dies. Black shank in its first year of occurrence is easily confused with other troubles like bacterial wilt.

Black shank appeared near Quincy, Fla., about 1915, but it was not identified until some years later. In 1924 the situation in the Florida shade-tobacco area became desperate, and remained so until resistant varieties could be developed. Only a type resistant to black shank is grown there.

Black shank appeared in North Carolina near Winston-Salem about 1921 and spread slowly. It was identified there in 1930, and the damage built up with increasing rapidity. Growers there tried without great success to reduce losses by using long rotations. Resistant flue-cured varieties, which became available after 1941, relieved the situation, even though they were less desirable agronomically than the best susceptible varieties.

Black shank appeared in eastern North Carolina in 1937. By 1945 it was a major problem. Within 10 years it built up to epidemic proportions. Growers whose farms became generally infested had to discontinue growing susceptible varieties. Black shank was found in central Tennessee and Kentucky in 1934. It became serious in 1951, and growers looked to the development of resistant varieties for solution to the problem.

One cannot forecast with certainty how black shank will behave in a new area. In the Florida shade-tobacco area and in North Carolina and Virginia, once a farm or field became infected it remained infected, although a rotation of 5 or 6 years might reduce the infection to a trace. There is one locality in which the disease has never persisted the flue-cured area of east Georgia where black shank has been identified twice, in 1933 and 1947. Both times the infection disappeared without any effort on the part of growers. For reasons we do not know, the disease, which spreads so rapidly in North Carolina and Virginia, has not been able to establish itself in eastern Georgia and Florida.

Black shank has occurred also since 1948 in South Carolina, eastern Tennessee, Maryland, and Pennsylvania.

A word of caution to growers in areas where black shank is a new problem: The experience in the older areas has been that during the build-up period (which has been anywhere from 7 to 15 years) growers often have had a false feeling of security. A moderate amount of rotation has worked quite well, and losses have been limited for a few years. After the epidemic stage was reached, however, rotation was less successful. It has been the same with regard to resistance in plants. In the early years even a little resistance stood up very well. After disease infection had accumulated, the need was for much higher resistance.