10 The Bulletin. 



Symptoms. — The leaves turn yelloAv and then brown, becoming dry 

 and dropping from the plants; these are often stunted in growth. It 

 usually occurs in certain sections of a field, all plants in the area showing 

 the condition, which shades off at the borders of the area. The disease 

 is distinguished from wilt by the absence of any discoloration of woody 

 part of the stem, and from root-knot by the absence of the galls. _ Red 

 spider injury to the leaves is frequently called "red rust," and is an 

 entirely different trouble. 



Cause. — This disease is not caused directly by any organism, although 

 certain weak fungi may establish themselves on the already weakened 

 leaves, and perhaps hasten their destruction. The proper functioning 

 of the leaves is deranged through unfavorable soil conditions. These 

 may be: (1) lack of water; (2) lack of drainage; (3) lack of food ma- 

 terial, especially potash, and (4) lack of humus. The trouble prevails 

 mostly on light sandy soils, particularly in places where there is a good 

 chance for teaching. Prolonged drouths after heavy rains are apt to 

 develop "rust" prominently on soils of the types indicated. 



Control. — Try to determine which ones of the factors enumerated 

 seem to be responsible. Humus may be added in the form of stable 

 manure or of green crops turned under. Use potash and phosphoric acid 

 as a fertilizer at a rate of something like 300 to 800 or more pounds to 

 the acre to supply the plant food deficiencies. Drain wet lands. Deep 

 preparation of the land and frequent shallow cultivations will help to 

 lessen the trouble. 



COTTON WILT. 



Distribution in North Carolina. — This disease is known to occur in 

 Anson, Davidson, Duplin. Johnston, Lenoir, Mecklenburg, Moore, Nash, 

 Pitt, Richmond, Robeson, Scotland, and "Wayne counties. It is prob- 

 ably in small areas in each of these as yet. 



Plants Affected. — Cotton and okra. 



The disease is known also as blackheart and blackroot. 



Symptoms. — The leaves may wilt suddenly, or may turn yellow slowly 

 and drop. Affected plants are usually somewhat stunted in growth, and 

 bolls may be poorly formed. On cutting across the stem dark brown dis- 

 coloration of more or less of the wood can be seen. Many of the roots 

 are blackened or dead. It may appear at any time after the cotton is 

 about eight inches high. 



Cause. — The fungus, Fusarium vasinfectum, enters the roots from 

 the soil, grows upward in the sap tubes, discoloring and clogging them, 

 and producing the wilt symptoms. 



Dissemination. — The fungus can live in the soil for a number of 

 years and may be transferred in even small amounts of contaminated 

 soil. Light sandy soils offer conditions best for its development. A 

 stable may harbor the fungus in the manure for a long time if once con- 

 taminated. Spores are produced on the surface of dead stalks in the 

 field, and some of these may become lodged in the lint, and remain in 

 the fuzz of the seed. But on the whole the chances for seed to act as a 

 carrier seem rather slight. 



Infection is through the root system in practicallv all cases, and is 

 greatly favored by nematode injury to the roots. There is apparently 



