Proceedings of the South & East African combined agricultural, cotton, entomological and mycological conference held at Nairobi, August, 1926

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Monograph

Identifikator:: 1738588467

URN:: urn:nbn:de:zbw-retromon-115043

Document type:: Monograph

Title:: Proceedings of the South & East African combined agricultural, cotton, entomological and mycological conference held at Nairobi, August, 1926

Place of publication:: Nairobi

Publisher:: East African Standard

Year of publication:: 1926

Scope:: VI, 337 Seiten; Ill.

Digitisation:: 2020

Collection:: Economics Books

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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part IV. Etomology & Mycology

Collection:: Economics Books

2. ENCLOSURE TO PART 1V. ~ We seem to be somewhat in the dark as to which of the fungi and ‘bacteria are true wound parasites, and which merely saphrophutes, although several can no doubt be relegated to the latter category. The position appears to be that there is a fungus and bacterial complex associated with certain forms of internal boll disease, distinct from the diseases caused by Bacillus malvacearum and Phytophthora (Soft Rot), and that so far experiment indicates that this complex is dependent upon a breach in the carpel to obtain access to the interior of the boll. The composition of the complex appears, however, to be far from uniform. Furthermore, no definite distinction appears to have been established between lint staining and obvious boll rot, and the two lesions are commonly described under the same heading. All this is unsatisfactory in one particular, namely that it commonly leaves the investigator without a means of identifying a given form of staining or discoloration in a specific manner. To give an example, the small plots of cotton at the Agricultural Experiment Station, Salisbury, show practically 100 per cent. stained lint this season, and on one at least of these plots, which has been under close observation, the agency of Dysdercus or other sucking insects large enough to pierce through the carpel may, it is thought, definitely be ruled out. Moreover, the stained bolls in most cases afford no indication whatsoever of any perforation of the carpel nor does the distribution of the stain show any relation to a hypothetical puncture. It is located at the bases of the locks, all of which are involved. The lint is adherent to the carpels at the base and a portion tends to remain behind when the lint is picked in the ordinary way. Apart from this the bolls have not opened properly, and most of the lint in the opened bolls remains compacted. ; The crop has been very slow in maturing, the elevation at Salisbury being probably too high for successful cotton culture in most seasons. On general considerations one would be inclined to attribute the condition of the cotton to physiological causes, but the staining answers well to the description of this trouble as shown to be transmitted by Dysdercus. It is here that the lack of a means of specific identification of the disease transmitted by Dysdercus is felt. Reports throughout the Colony are to the effect that staining is extremely prevalent this season, and heavy losses are anticipated. Dysdercus spp. have certainly been very prevalent on many farms, and in many cases have clearly attacked the stained bolls previous to opening. At the same time the season has been an abnormally wet one, and the plants have suffered to a considerable extent on this account. In the light of experience at Salisbury caution appears to be indicated in attributing all this staining to Dusdercus. It is also noted that Mr. H. C. Sampson in his report to the Empire Cotton Growing Corporation, 1922, describes lint staining in Nyasaland in a way which i$ in agreement with experience in Southern Rhodesia, and does not suggest Dysdercus as the cause in all cases. The influence of the season in reference to the trouble is also emphasized by Mr. Sampson. Moreover, the connection between Dysdercus and boll diseases does not appear to be clearly recognised in the South African Union, if one may judge by Mr. G. C. Haines’ paper read before the conference of entomologists at Pretoria last year. Dysdercus in point of fact has been regarded as a minor pest =d40

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