TOBACCO DISEASES AND THEIR CONTROL. 



39 



Control. — Measures to prevent this disease are not as yet satisfac- 

 torily worked out. Land likely to yield the disease should not be 

 used for tobacco. If such soils must be used, it is probable that 

 proper drainage, subsoiling, and cultivation conducive to good tilth, 

 together with well-balanced fertilization, will be very useful in 

 preventing it. 



SAND-DROWN. 



Description. — A blanching or chlorosis, especially of the lower 

 leaves of tobacco plants grown on very sandy soils during seasons of 

 excessive rainfall, has long been known as sand-drown. This disease 

 occurs particularly in the tobacco districts of North Carolina, but 

 also may be found in the sandy soils of other States, as in the Con- 

 necticut Valley. This trouble is most likely to be confused with 

 another nutritional symptom fairly common in tobacco and known 



Fig. 21. — A badly frenched field of tobacco. This disease is commonly characteristic 

 only on certain types of soil or under certain soil conditions. 



as potash hunger or potash starvation. Potash hunger may occur, 

 however, on almost any type of soil and under quite variable condi- 

 tions of rainfall. The blanching in potash hunger is usually more 

 localized in small areas, quite yellow in color, and sometimes over- 

 cast with bronze or copper colors, together with crinkling or curl- 

 ing of the leaves. Sand-drown is characterized, on the other hand, 

 by more or less complete and uniform blanching until the leaf 

 is practically white in late stages except for the midrib and veins, 

 which retain their color (PI. XV). The blanching usually starts 

 at the tip of basal leaves, proceeding downward along the margin 

 and inward between the veins toward the midribs. Crinkling and 

 curling are not common, but occasionally local areas die out, as in 

 the case of potash hunger or leaf-spot diseases. 



Cause. — Sand-drown has recently been shown to be due to a short- 

 age of magnesium in the soil or in the fertilizer used. Most soils 



