o4G Journal of the Depaktment of A(;i{iculture. — Dec, 1922. 



Report No. VI. 

 BOTANY AND PLANT PATHOLOGY. 



Irtiiifi (liief af Pin'sioii: Ethee M. ])()n)(;E, M.A., D.Sc. F.Tv.S. 



1. I'hint /'(if/iiil(»(/i; (iiul M jicoloji fi . — Tlie work on llic wastage in 

 export citrus fruit was continued, and tlie results of tlie investi;,vation 

 T.'ere published in Bulletin ]N^o. 1 of 1922. 



The situation with rej'.ard to citnis cankei' eradication continued 

 tj be stvtisfai-tory. Durino- the year only four trees were found 

 infected, and tliese were all on the farm Buft'elspoort, in the Rusten- 

 burg District. During 1920-21 six trees were found on three diiferent 

 farms ; on two of these no further infection occurred during the 

 following year. An extensive field experiment is being carried out to 

 test the advisability oA replanting citrus trees after three to five years 

 in orchards where infection v\'ith citrus canker has occurred. 



Certain other citrus diseases, including verrucosis and scaly bark, 

 are also under investigation. The latter disease has only been 

 observed in this country Avithin the last two years, and in certain 

 areas appears to be spreading with considerable rapidity. 



An outbreak of wart disease in potatoes (Stjnchitriutn cn(J(>})i(>- 

 ficAivi Perc.) occurred in Natal. An inspection of potatoes on the 

 farms in the affected area was organized as soon as the matter was 

 reported, and is still in progress, but the origin of infection has not 

 yet been discovered. Potatoes showing wait disease have up to the 

 present only been found on two adjoining farms in the Impendhle 

 Division, Natal. These are fortunately stock farms, and the owners 

 only grow potatoes for their own use, so it is hoped that the disease 

 has not become more widely distributed. No cases of infection were 

 reported from the farms on the Boston area, near Impendhle, where 

 potatoes f4re grown in considerable quantities. 



Investigation \\o\\ was coiisideral)ly hampered during the year. 

 Subsequent to the resignation of Dr. van der Bijl, a mycologist from 

 Pretoria was transferred to Durban for two months, and the repeated 

 absences from headquarters of the Chief of the Division and Miss 

 Thomson in connection with the botanical survey, had the effect of 

 throwing the whole of the advisory Avork on to the shoulders of the 

 remaining members of the staff. As a result, very little progress was 

 made in the investigation of citrus diseases and A-arious other fungous 

 and bacterial diseases Avhich urgently need tittention. 



In connection Avith the advisory work many diseases of doulitful 

 or obscure origin Avere reported. Some of them are likely to prove oi 

 economic importance and require investigation, but it is not possible 

 to investigate many of these problems with the present staff". In 

 particular may be mentioned two diseases of peanuts ; in one case, 

 the plants turn yelloAv and die without ajiparent cause ; in another, 

 the apparently healthy plants bear a large crop of nuts entirely devoid 

 of kernels. 



