^54 



THE AGKIUULTUIIAL SEWS. 



Au.iUST 10, 1918. 



PLANT DISEASES. 



A MARKET DISEASE OF CITRUS FRUITS. 



In Pli\tifathi,lu,i_\\, Vol. VllI, No. -J, (_). T. Wilson, of 

 the University of Cincinnati, gives an account of a hitherto 

 undescribed disease common on Florida-grown limes on sale 

 in the Cincinnati markets. The matter has local interest 

 inasmuch as an afl'ection identical in the peculiar characters 

 described has been met with now and again, by the present 

 ■writer, on West Indian urange.s imported into Barbados. 



The aft'ected fruit is recognizable by the presence of 

 surface areas more or less discoloured, which are 8n]i>oth in 

 comparison with the normal surface, the colour varying from 

 a deepened yellow to copper colour, with the margin of the 

 *pot mostly brownish. Upon opening a diseased fruit an 

 abnormal odour can be detected. A distinctive fungus is 

 found in the fruits so affected. It has been cultivated by 

 "Wilson, and the disea.se reproduced in inoculated limes. 



When the fruit is surface-sterilized and left for develop- 

 ments, no soft rot takes place, but it gradually dries up and 

 becomes mummified, the e.xterior blackening, and the con- 

 tents being converted into carbonaceous material mainly 

 constituted of dense black mycelium. In this condition the 

 fruit may be kept for months, if jjrotected from scavenging 

 insects, and, according to W^ilson, the mycelium retains its 

 ■vita.ity. Xo fructification has been observed by Wilson, nor 

 <lid the present writer succeed in several attempts to induce 

 spore formation. 



" W^N. 



POWDERY MILDEW OF ROSES. 



Several requests have reached this Office recently for 

 information as to the control of rose mildew. At this time 

 of the year, when new shoots are put out freely, and may 

 develop under conditions of considerable atmospheric humid- 

 ity, the trouble is especially common. The young shoots and 

 leave.-< are externally invested with grayish-white mycelium 

 and conidia, which give them a powdered appearance; the 

 leaves are more or less discoloured and crumpled. 



Certain types of ro.se, especially the ramblers, are very 

 susceptible to the disease, and the best way of avoiding the 

 trouble is to grow others mor.j resistant, of which there are 

 «nough and to spare. It may, however, be effectively con- 

 trolled, on plants which are otherwise in good condition, by 

 the u.se of flowers of sulphur. This material may be diluted 

 about one-third with powdered air-slaked lime if desired. 

 According to recent writers in America, some advantage has 

 been gained by using a mixture of 90 parts of sulphur and 10 

 parts of arsenate of lead. The powder .should be dusted on 

 in the early morning, while the foliage is damp, a day being 

 chosen which seems likely to afford hot sunshine without 

 showers. This treatment is much more effective than the 

 use of Bordeaux mixture, and avoids any unsightly deposit 

 on the leaves. 



SEED TREATMENT AND ANGULAR 



LEAF-SPOT. 



In view of the importance to cotton growers of 

 angular leaf spot and the related boll-rot due to Backrium 

 mithacearuiii, a paper on the similar spot of cucumber, 

 caused by linderiiim lachrymans, with reference to the 

 effects of seed treatment, has considerable local interest. 

 Information as to the means by which B. malvacearum is 



carried over from season to season is lacking, and pending 

 the needed investigation some analogy with the cucumber 

 disease may be assumed. 



W^ W. Gilbert and M. W. Gardner, in Phytopatliology, 

 Vol, VIII, No. .5, give particulars of large scale tests of the 

 theory that overwintering may take place on the seed. Seed 

 was surface sterilized by various means, the mo9t satisfactory 

 of which proved to be immersion for five minutes in corro- 

 .sive sublimate (mercuric chloride) 1:1, OOc, followed by fif- 

 teen minutes washing. Trials were made on whole fields, 

 some in which diseased cucumber crops had been grown the 

 previous year, others with clean soil. The use of treated 

 seed in infested soil, and of untreated sr'ed in clean soil led 

 to the appearance of the disease in July, and its destructive 

 prevalence by August 1. In fields planted with treated seed 

 on clean soil, the disease made only a belated appearance at 

 a few isolated points, from which it slowly spread, but 

 never attained to destructive prevalence. As all the ground 

 was cultivated by the same workmen, the authors suggest 

 the possibility of such infections as did occur on the latter 

 fields having started from infective material conveyed on 

 implements or clothing. 



The conclusions to be drawn from the experiment are 

 these: that infestations may arise from infested soils or from 

 infested seed; that surface sterilization of the seed removes 

 the latter .source of infection; and, in general, that crops 

 grown from treated seed planted in clean soil should remain 

 free of the disease, except so far as it is incidentally intro- 

 duced from outside during their development. 



The practice of treating cotton seed with corrosive sub- 

 limate appears to have largely fallen into disuetude in these 

 i.slands. It is probable that the benefits which may in some 

 cases be obtained are worth the amount of trouble which the 

 treatment entails. 



W.N. 



STUDIES OF LEGUMINOUS PLANTS. 



The results of preliminary studies by X. Gangulee oq 

 some aspects of nitrogen fixation in certain leguminous plants 

 suitable for green manuring in Poona, recorded in the Pooiia 

 Agriciiltuml College Afagaziiie, 8 (1917), receive reference in 

 the Experiment Station Record for June 1918. From these 

 results it appears thf^t the experiments were planned to 

 study the following points; At what stage of growth nodule 

 development and, hence, nitrogen fixation begins; the iiuan- 

 titj of nitrogen fixed in the whole plant at various stages of 

 growth; the proportion of nitrogen fixed at various stages 

 of growth normally occurring above and below the ground, 

 the latter being only available with ordinary cultivation for 

 an increase in the permanent fertility of the land; and the 

 influence of available potash, phosphoric acid, and lime on 

 nodule development, and their effect on the quantity of 

 nitrogen fixed in the whole plant at various stages of growth. 



As certain of the plants experimented with are at 

 present grown in the West Indies for green-dressing purposes, 

 a summary of the conclusions arrived at in connexion with 

 these is given below. 



Dolielios I.ahlab (bonavist bean) began nodule forma- 

 tion about fifteen days after germination, chiefly on the 

 primary roots. Nodules formed on the smaller roots except 

 at the extreme ends, but gradually disappeared as the plant 

 approached maturity, with a few large nodules (about the 

 size of a pea) remaining on the larger roots. The nitrogen 

 in the plant gradually increased from 21 percent, in the 

 dried seedling to froni VI to 39 per cent, in the dried plant 

 at the flowering stage. The portions above ground con- 



