415 



Probably the much dread Mafuta disease of the sorghum millet 

 (Andropogon sorghum) in German East Africa belongs here. The word 

 Mafuta means oil. Honey-like excretions are found on leaves and stems. 

 These give rise to a sooty coating^. Other plants also suffer especially in 

 times of drought. 



Heart Rot and Dry Rot of Fodder and Sugar Beets-. 



The heart rot of the sugar beet should be considered as a phenomenon 

 usually related to honey dew. It is found usually in hot Julys in rainless 

 periods and is characterized by the death of the heart leaves. These have not 

 grown to half their norm^al size. The dying foliage suddenly becomes black. 

 In severe attacks the whole leaf area dies, but, as a rule, the plants develop 

 new foliage. In addition to the affection of the leaves, the body of the 

 beet is attacked by a decomposition or dry rot. The beet, near its head end, 

 has spots which can deepen as the tissues decompose, and finally destroy the 

 beet. Of greater agricultural significance in this connection is the fact that 

 a part of the non-reducing sugar disappears from the beet and another part 

 is converted into reducing (grape) sugar^. If the rainy weather sets in at 

 the right time, the dead tissue can be thrown off through the formation of 

 cork. 



If the healing process does not set in soon enough, so that a long con- 

 tinued autumnal dampness can exercise its influence on the decayed places, 

 the process of destruction of the beets, which are poorer in sugar, is also 

 continued in the storage pits. 



Most observers are incUned to seek the cause of the trouble in fungi, 

 since mycelium is often found in the diseased heart leaves*. Frank 

 especially defended the fungi theory and wished to make two species re- 

 sponsible for it : Phoma Betae, Frank^ and Fusarium beticola, Frank. 

 It is certain, however, that the first stages of the disease of the heart leaves 

 are without fungi and bacteria, and the parasites later, during damp weather, 

 occasion an advance in the destruction of the tissue. However, when the 

 beet plants are healthy, the fungi cannot attack them. Only when evapora- 

 tion is sufficiently increased and the absorption of water sufficiently de- 

 creased do the conditions arise which predispose the plants to attack by 

 fungi. 



Practical workers state that the addition of lime also in the form of 

 waste lime favors the attack of the disease. We have very instructive 

 field experiments^ along these lines in which some areas were limed, and 

 some not. Where lime was used, the beets were diseased, where there was 

 none, the crop was healthy. 



1 Busse, "W., Weitere Untersuchungen iiber die Mafuta-Krankheit der Sorghum- 

 Hirse. Aus "Tropenpflanzer," cit. Zeitschr. f. Pflanzenkrankh. 1902, p. 82. 



2 See Vol. II. p. 240. 



3 Frank, A. B., Kampfbuch. 1897, p. 131. 



4 Prillieux et Delacroix, Complement a I'etude de la maladie du coeur de la 

 Betterave. Bull. Soc. mycologique. VII, 1891, p. 23. 



5 syn. Phoma sphaerosperma, Rostr., Phoma Betae, Rostr., Phyllosticta tabifica, 

 Prill, et Del. 



6 Zeitschr. f. Pflanzenkrankh. 1895, p. 250, 1896, p. 339. 



