THE AGRICULTURAL ISTEWS. 



March 10, 1917. 



PLANT DISEASES. 



CITRUS CANKER IN SOUTH AFRICA. 



Miss Ethel M. Doidge, Mycologist to the Union 

 Depanment of Agriculture, South Africa, gives an account, 

 in Scieyu-e Bulletin No. 8 of the Department, of the 

 origin and hi.story of citrus canker in that country. 

 In 190.5-6 a number of grape-fruit trees were imported 

 from Florida and planted in the Govei'nment Experi- 

 mental Orchard at Warnihaths, in the Transvaal. When the 

 trees began to bear in 1908, a few spots were noticed on the 

 fruit, and in the wet summer of 1908-9, the disease began 

 to spread with incredible rapidity and went right through 

 the orchard. Vigorous remedial measures were applied and 

 the trees were repeatedly sprayed with ammoniacal copper 

 carbonate. In spite of this, the whole lemon and orange 

 crop of 1909 was too unsightly to sell. In liUO the trees; 

 were pruned and sprayed with Bordeaux mixture, which 

 checked the disease at once. The new growth was healthy, and 

 the 1911 fruit crop free from di.sease Spraying was repeated 

 in 1911 and 191l', and nothing more was seen of the disease 

 until 191(1, when slight infections were noticed on a few 

 grape fruit trees. 



This success of Bordeaux spraying is in direct contrast 

 to the recorded Florida experience, but agrees with the Texas 

 experience described by Grossenbacher (Phytopathrjlogy, 

 VI, p. 29). 



A few other Transvaal orchards have been found to be 

 affected, and in each case the disease can be traced to the 

 importation already referred to. 



Miss Doidge has established, by cultural method.s, the 

 identity of this causative bacterium with Pseudornovas citri, 

 Hasse, now accepted as the cause of the Florida outbreak. 



The story is not without its moral for West Indian 

 planters in general. So far as this particular di-sease is 

 concerned, the legislative action taken should be sufficient, 

 provided that the regulations made are carefully enforced. 

 A number of citrus plants imported from Florida before 

 the existence of this disease was known have been examined 

 at the Dominica Gardens by the writer, and have shown no 

 sign of infection. 



A COLLAR DISEASE OF PIGEON PEAS. 



Mr. J. C. Moore, Superintendent of Agriculture, firenada, 

 has forwarded a report by Mr. Malins-Smith on a disease of 

 the pigeon pea bush, Ctijantis indicus, which has caused 

 somewhat .serious losses in the island of Carriaeou. The 

 disease has a scattered distribution but is held to be 

 responsible in some areas for the death of as many as fifty 

 trees to the acre. 



A number of specimens have been forwarded for 

 examination, and from these it would appear that the seat 

 of the affection is in the stem and roots in the neighbourhood 

 of the collar. Several fungi were present on the specimens, 

 but of the.se the only one which appeared to be quite 

 general, and to be most closely associated with the lesions 

 found, is an Ascomycete which forms a black stroma through- 

 out the bark of the affected regions, and produces very 

 numerous perethecia and pycnidia in the outer bark. 

 The perethecia occur in dense clusters, more or less united 

 towards the base, and have rather long necks which project 

 through cracks in the outer bark. As the latter weathers 



away the perethecia themselves become exposed. Both 

 pyenospores and ascospores are ejected in white tendrils. 

 The former are oval or oblong, the latter are somewhat 

 irregular in outline but tending to be coffin-shaped Both are 

 unicellular and hyaline. The wood becomes filled with 

 dark coloured hyphae which give to it a slaty grey appearance. 

 Some of the thicker stems were split radially and fluted, owin" 

 to the development of longitudinal ribs of new wood on 

 the surviving sectois of previously diseased stems. It would 

 seein that the disease is one that only makes headway 

 at certain seasons. Inoculation experiments will be made 

 with the fungus when the conditions appear more suitable 

 than they are in the present dry weather. 



As the di.-<ease is present mainly or entirely in peasant 

 holdings, an attempt is being made with the aid of a grant of 

 £10 from the Grenada Government t ■ reduce the 

 prevalence of the disease by digging up and burning the 

 affected plants under official supervision. 



Stem or root diseases of pigeon pea are rather frequent 

 in the.se islands, but so far as is known to the present writer 

 they have been sporadic in their occurrence and have received 

 little attention. It is desirable, now tint the subject has beerk 

 brought to notice, that the occurrence of any cases should be 

 re]iorted to this Office for investigation. 



POISONING A COCO-NUT PALM. 



Reference has been made in this Jnurnal (Vol. XV, 

 p. 254) to the poisoning of trees with sodium arsenite, and 

 particulars given of a method of application which has been 

 adopted with success in the case of the ordinary (dicoty- 

 ledonous) lype of tree. 



The writer recently had occasion to test the eff'ect of 

 the poison on a well grown but almost barren coco-nut palm 

 some twenty years old. With a 1-inch auger a hole was bored 

 slanting downwards into the base of the stem, penetrating 

 about two-thirds of the diameter. About li oz. of sodium 

 arsenite was introduced the hole filled with water, and 

 plugged. The water was renewed two or three times in the 

 next few days. At the end of one week the expanded leaves 

 had assumed a reddi.sh colour: in two weeks all the leaves 

 were obviously dead, and towards the end of the third week 

 the central column, including the bud, came to the ground. 



There has been some dispute, in discussions, of the 

 effects of coco nut root di.seases, as to whether the rotting 

 of the bud obsir\ed in many cases was to be considered as a 

 consequence of the root trouble, or of an infection with 

 the bud-rot disease. 



It is noteworthy that in this poisoned tree the soft 

 tissues about the base of the central column became invoked 

 in a putrid soft n>t, and this so quickly, that in less than 

 three weeks the whole heart came away. The weather during 

 the period was very dry and windy, and the tree was in an 

 exposed position There can hardly in this ca.se be any 

 question of infection with a special bud-rot organism, since 

 the di.sease is quite unknown in Birbados. 



Excepting the leddening of the outer leaves, the genend 

 appearance of the tree was exactly that described as typical 

 for the form of bud-vot disease which first affects the heart. 

 The experience emphasizes the need for caution in attributing 

 this type of failure to the pre.sence nf the specific bud-rot 

 disease. Apparently the infectious nature of that affection is, 

 in the present state cif our knowledge, the inly distinguishing 

 feature on which reliance can he placed. 



W.N 



