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THE AGRICULTURAL NEWS. 



Api'.il 6, 191S. 



PLANT DISEASES. 



CITRUS BLAST. 



A si'cond important bacterial di>ea>e of citrus trees was 

 announced two j-ears ago as having made its api)earance in 

 California. It was found to be due to a new bacterium to 

 wbiih the name /^lu/i'riinn <i/i-(u\f<iii\iif, \^2e, was applied. 

 The affection itself received the name of Citrus I'.last. A 

 descriptive account of the disea.se in it.s recent phase is given 

 by Robert AV. Hodgson, of the I'niversity of California, in 

 the Qtttjrter/y BulUtiii of t)u State r/uiit Board of Flariihi, 

 dated January 1918, from wpich the following particulars 

 are obtained. 



Since the season of 191-3, when it was confined to only 

 two local areas, the disease has spread very rapidly and has 

 now been reported from practically all parts of the citrus- 

 producing districts of Northern and Central California. It 

 is described as having been particular!}- virulent in 1917. 



Infection is apparently confined to new spring growth 

 i.r unseasoned wood produced the pievious season, and occurs 

 mainly at the junction of the petiole and blade of the leaf. 

 Apparently a certain amount of infection also occurs at the 

 tips of the very young leaves and tender shoots. Upon 

 infection the leaf turns pale yellow, then darkens irregularly 

 in spots, and wilts in place, where it later shrivels and dries 

 still hanging to the shoots. Once established the disease 

 progresses rapidly down the shoot toward the older wood. 

 Only relatively new growth is atfected, the older limbs 

 possessing greater resistance. The young shoots ate often 

 killed back to the older wood, including a portion of the 

 bark about the base of the shoot. At these points character 

 istic lesions are formed. It is not unusual to find a branch 

 .several feet long with every node atfected in this manner. 

 If the disease is virulent and conditions are favourable, as 

 was the case last season, it may attack branches of the previous 

 season's growth as large as ^,inch in diameter, killing 

 them back for a distance of .several feet. The killed area 

 about the base of the infected leaf or .shoot varies consider- 

 ably in size, and is ordinarily more ri)- less irregular in shape, 

 frequently extending some distanie ak>ng the stem. In the 

 case of younger growth girdling may occur about the point of 

 infection with the resultant death of the shoot to this point. 

 The rapidity with which the disease spreads is remarkable, and 

 only a few days of the proper weather conditions are rei|uired 

 for serious damage to ajipear. 



The disease is only active when warm damp weather 

 during a flush of grewth supplies favourable conditions 

 for its rapid development. In California these condi 

 tions rarely occur .save in spring, and with the coming 

 of the dry season the disease becomes i|uiescent. In 

 the period which follows, the lesions often e.xude a 

 pinkish resinous gum or bacterial slime, and such lesions 

 and all the dead ti.ssues later take on a characteristic 

 dark-red colour. The dead twigs when dry are very hard 

 and tough. I)uririg the healing process wound callus is 

 rteveii'ped at the infected node.", which raii;cs the dead lesions 

 up in the form <A scab like masses. These are .sloughed 

 f>H' in the course of time, leaving very characteristic scars 

 which are visible for several years. 



What would be the form and effects of the disease in 

 a climate which perinitted it a longer period af activity is at 

 present unknown. Its effect in California is to kill back the 

 fruiting twigs first grown and so to delay the setting of fruit 

 until they are re[)laced by new growth. 



Little or nothinj! is kiKiwii as yet of effective methods 

 <>i coctrol. 



THE MOTTLING DISEASE OF CANE IN 



PORTO RICO. 



An account of this new and serious disease of sugar- 

 cane, based on an article by Mr. John A. Stevenson in the 

 /.oiiisiaiKi J'/iiiili-i\ was given in this Journal (Vol. .\^'I, p. 

 S.'^'G). In J'/nio/'atho/ooy for December 1917, the same author 

 gives a later and more complete description. 



The information as to the geogra|ihical distribution ct 

 the disease is especially interesting, and is here quoted in 

 full: 'The trouble first appeared in the Western end of 

 the island, in the region between Arecibo and Agua- 

 dilla, and in the summer of 19U) was practically 

 confined to that area. Since that time not only have it.=< 

 ravages continued in the original territory, but its boundaries 

 have been extended so as to include an area extending from 

 near Rayamon to Anasco, or appro-ximately a (luarter of the 

 island. 



'It has not been possible as yet to ascertain how long 

 the disease had been jiresent before the first report was 

 received, but certainly a year, so that as near as is now 

 known it has been active about three years. 



'The trouble is as yet confined to the upper reaches of 

 the river valleys, to small enclosed inland valleys, and 

 particularly to fields among the foot-hills. The broad stretches 

 of the coastal plain, but little above sealevel, are still free 

 of ilisease, although they are planted to the susceptible 

 varieties of cane, and form great continuous areas. The 

 greatest damage hds occurred in the rolling stretch of country 

 between Arecibo and Aguadilla, a region which suffers inucli 

 from drought. Cane culture has been abandoned on hundreds 

 of acres. 



'All observations .show an apparent tendency of the 

 disease to occur in upland fields. In its eastward progress 

 it has apparently jumped from valley to valley, some distance- 

 back from the ocean, or has appeared sporadically rither than 

 working along through the continuous coastal fields.' 



It is agreed that the monetary loss already runs into 

 hundreds of thousands of dollars. An instance is given of 

 one Central, which in spite of 3,0(i0 additional acres planted 

 last > ear, and the purchase of some thi lU-sands of tons of cane 

 from outside districts, dropped behind its previous year's 

 production by more than half a million pounds of sugar. 

 A considerable number of small planters have been complete- 

 ly forced out of cane growing in two years' time. 



The one marked and constant .sym|itom of the disease, 

 and the one l>y which it is easily recc'gnized, is the peculiar 

 mottling of the leaves, consisting of innumerable white or at 

 times yellowish si)ots and stri|ies with irregular indefinite 

 margins. The ground colour may be normal green, but 

 more often is yellow or yellowish green. 



The mottling is apparent as soon as the leaves unfold. 

 In the ratoons the second type of lesion, canker of the 

 stalks, appears. At first there are linear spots .scmiewhat 

 sunken, and brown in colour. They soon become ashen 

 or dull grey, and often coalesce to form continuous patches 

 practically covering the surface between the .joints, but 

 never cioasing the latter. They are (juite superficial. 



Not only is tliere a lack of juice in cankered canes, but 

 what does occur is of such an objectionable nature that the 

 centrals refuse to receive affected cane. 



The cause of the disease remains obscure. All direct 

 measures of control have proved useless. In rotation of crops, 

 a practice previously uiiUnown in I'orto Rico, lies the only 

 visible |>rospect of saving the sugar industry in the affected 

 districts. 



