and Magazine of the Ceylon Agricultural Society.— April, 1910. 



373 



BACTERIAL BLIGHT IN COTTON. 



(Bacterium malvacearum.) 

 Notes by J. Stewart J. McOall, 

 Director of Agriculture, Nyasaland. 

 This bacterial disease of cotton is by far the 

 worst euemy of Egyptian cotton cultivators in 

 Nyasaland, and in the past season has reduced 

 the output of several estates by at least 60 

 per cent. The disease was first noticed by the 

 writer in April, 1909, infecting ratoon cotton 

 on the late Oceana Consolidated Oo.'s Estate, 

 Kaorabi, Chiromo, and judging from corres- 

 pondence on the subject the ultimate cloeing 

 up of the said company's interest in Nyasaland 

 may be largely attributed to the ravages of this 

 disease. Later in the season the writer observed 

 it in several localities including Port Herald, 

 Chiromo, Maperera, M'piiubi and Liwonde. 



Bacterium malvacearum is prevalent in the 

 south-eastern States of America, and was largely 

 responsible for the repeated failure of all at- 

 tempts to cultivate Egyptian cotton in this 

 section of the cotton belt. 



Egyptian and Sea Island cottons are peculiarly 

 subject to it, but varieties of American Upland 

 cotton have developed such a high degree of re- 

 sistance that one might presume Bacterium mal- 

 vacearum is an American disease : it is compara- 

 tively rare in Egypt. 



Symptoms of the Disease.— The bacterial 

 disease is found on different parts of the plant 

 producing various symptoms and receiving var- 

 ious names, such as black arm, boll spot, black 

 rust, angular leaf spot, &c, depending on the 

 point of attack. The disease first appears on 

 the leaves where it produces the characteristic 

 angular leaf spot, first watery green and ulti- 

 mately reddish black in colour. The distribution 

 of the diseased angle spots on the leaves is irre- 

 gular, but most numerous along the veins and 

 more especially towards the base close to the 

 petiole by which it enters the branches. It 

 rapidly causes the leaves to shed and the bacteria 

 may also gain entrance to the branches through 

 the leaf scar, ultimately producing irregular dark 

 lesions on branches and giving rise to the name 

 black arm . Once the disease has entered the crop 

 it spreads with wonderful rapidity throughout 

 the field ; in a short time the young branches 

 carrying the flowers and bolls wither and die, 

 the crop turning black and leafless as if attacked 

 by frost. In Nyasaland the bacteria seldom pro- 

 duce boll rot, but sometimes a plant mildy at- 

 tacked by angular leaf spot is also attacked by 

 anthracnose fungus, the latter gaining entrance 

 through the bacterial spots or lesions and 

 rapidly causing boll rot. Fortunately for Nyasa- 

 land the two diseases have practically no facul- 

 tative relationship as anthracnose on the Shire 

 river is rare in comparison with parts of the 

 American cotton belt. It is a fact worth recording 

 that boll rot caused by anthracnose is more fre- 

 quently met with in the highlands, and thus 

 bears out the experience of American investi- 

 gators who consider that the severity of attack is 

 largely in relationship to the rainfall, always being 

 worst in districts with a heavy rainfall. Speci- 

 mens of diseased cotton from Nyasaland exam- 

 ined by Prof. Orton of the Bureau of Plant 

 Industry, Washington, U. S. A., were found to 



contain a Fusarium in connection with the bac- 

 terium, but those fungi are generally considered 

 saprophytic and therefore in no way responsible 

 for the disease, but simply living on the diseased 

 tissues of the plant. 



Local Observations. — At the commencement 

 of Egyptian cotton cultivation on the Shire river 

 it was the general practice to sow cotton at the 

 advent of the rains in November or December. 



This cotton always looked well until March or 

 April when it went off suddenly in patches; 

 some gardens being complete failures after giving 

 promise of large crops. This going offwas gene- 

 rally attributed to cold or wet, and no doubt they 

 were predisposing causes as it was generally after 

 rain that the crop began to show symptoms of 

 disease. On making an extensivesurvey of the 

 entire Egyptian crop in the districts already re- 

 ferred to, the writer found the severity of the di- 

 sease to be subject to the following conditions: — 



la Situation of cotton garden ; II. Time of 

 sowing ; III. Variety of cotton grown. 



I. Situation of Cotton Garden. — It was 

 noticed that cotton gardens at or below the 

 level of high river mark were most severely 

 attacked. Everyone who has cultivated cotton 

 knows that a cotton plant is very sensitive to 

 stagnant water, and can withstand drought far 

 better than excess of moisture. Many sections 

 of the land bordering the Shire river are un- 

 suitable for Egyptian cotton cultivation on ac- 

 count of adverse soil conditions such as un- 

 suitable texture, lack of aeration, acidity, etc., 

 and therefore the writer does not recommend 

 planting Egyptian cotton except in free alluvial 

 soils with good natural drainage. The severity 

 of attack is controlled to a great extent by the 

 health of the plant at the season when the bac- 

 teria is sporing ; this explains why weak cotton 

 growing in wet low lying hollows is first at- 

 tacked and why the disease always seems to 

 spread from such centres. 



II. — Time of Planting. — The natural time of 

 sowing in countries with distinct dry and wet 

 seasons is the commencement of the rains, but 

 this is not always practicable and Egyptian 

 cotton on the Shire river is a case in point. 



At the commencement of cotton cultivation in 

 Nyasaland planters naturally sowed in Novem- 

 ber and December, but with discouraging results 

 asa large percentage of the cotton died off with 

 this disease. After experimenting it was found 

 that January and February sown cotton al- 

 though not producing such large plants, gave 

 a better return, as it was seldom severely 

 attacked by disease although growing in the 

 same gardens. The disease in both cases 

 always appeared in April and May indicating 

 those two months as the sporing season for 

 the bacteria on the Shire river, unfortunately 

 the very time when the plants may be checked 

 in growth as it is the beginning of the dry 

 season. When two crops of the same kind, 

 growing on the same soil present marked 

 difference of resistance to the same disease, 

 we can only attribute the greater degree of 

 resistance of the younger plants to their 

 more robust state at the time of attack. 

 It is undoubtedly the case that a plant which 

 has produced flowers and bolls profusely is 

 weaker in its vegetative parts than a plant 



