Vol. hi. No. 57. 



THE AGRICULTURAL NEWS. 



199 



DISEASES OF PLANTS. 



Citrus Trees. 



Mr. P. H. Rolfs ill Bulletin No. 52 of the Bureau of 

 Plant Industry (United States Department of Agriculture) 

 gives an account of some diseases of citrus fruits and trees 

 caused by Cofletoirif/mta ijloeosporioides. 



The fungus Las long been known to be the cause of 

 ' withertip ' on orange and lemon twigs, and the same fungus 

 causes a ' leaf spot ' of these and other citrus trees. It is 

 now shown by Mr. Rolfs that this fungus is also the cause of 

 the 'anthracnose' of lime (lowers and young fruits of lime 

 and lemon twigs, also of 'spot' of ripe lemons and ' canker ' 

 of limes. 



With the lime, infection usually occurs at the axil of 

 the leaf and the fungus then cuts off the stem, so that the 

 upper part falls over and either hangs down or drops off. 

 Gum, in such cases, is quickly formed at the wound and the 

 fungus does not spread down the twig. The fungus may 

 also enter by the terminal bud or by the leaves, in which 

 case the tip dies back for a distance or even as far as the 

 main trunk (wither-tip). The flowers may also be attacked, 

 in which case the disease may prevent any fruit being 

 formed on a tree. Young fruits may also be infected and 

 when this happens a large percentage of it falls. 



With the orange, the leaf is the first point attacked and 

 spots of various kinds are produced. From the leaves the 

 fungus spreads to the young twigs and gives rise to wither- 

 tip. The fruit of the orange, apparently, is not attacked. 



The following account of the treatment of lime trees 

 shows what can be done by remedial treatment for this 

 disease : — 



'During the past year experiments performed by- 

 Mr. if. S. Burbank, of Cocoa-nut Grove, Florida, at the Red 

 ilill fruit farm, with a view to protecting lime trees from 

 the attacks of this fungus, brought out some interesting 

 results. One tree under observation had been producing 

 limes for a number of years in a most [irolific manner, 

 but during the three years preceding 1902 the crop had been 

 a total failure, owing to the attacks of Colletotrichum gloeos- 

 porioides. Spraying with Bordeaux mixture was begun in 

 September 1902 and was continued at intervals as thought 

 advisable, and in less than a year the disease had been 

 almost entirely subdued, and the tree bore a heavy crop of 

 fruit. Other trees were also treated, as well as trees in 

 other groves, with good results.' 



In a small orchard, especially a young one, cutting out 

 diseased twigs and picking diseased leaves reduce the 

 disease considerably or may even eradicate it. The picking 

 and pruning must, however, be done thoroughly and at 

 frequent intervals. 



Thorough cultivation and manuring are of great value 

 in reducing the amount of damage done by the disease, and 

 also will reduce the probability of infection. 



Tobacco. 



In Bidktin No. 51 (Part 1) of the Bureau of Plant 

 Industry (United States Department of Agriculture), by 

 Mr. R. E. B. McKenney, a preliminary account is given of a 

 wilt disease of tobacco. 



The disease is apparently due to a fungus similar to 



those that cause wilt in cotton, water melon, tomato, etc. 

 It is a species of Fusarinni (^Neocosmospora). 



The disease does not appear until the plants have made 

 about one-thivd of their growth. The first sign is the sudden 

 wilting or drooping of one or more of the leaves ; this 

 wilting is permanent and is followed by a withering of these 

 leaves. Generally this is followed by wilting and withering 

 of all the leaves of the plant. Later, the base of the stem 

 blackens and rots and at the same time the roots will be 

 found blackened and often soft and ' mushy.' 



The Fumrium is a soil fungus and gains access to the 

 plant by the fine roots. 



Nothing can be done to save a plant once it has been 

 attacked, so that all methods must be preventive. 



Tobacco should not be planted on an infested field for 

 a period of five to eight years, as the Fusdviuni is capable of 

 living in the soil for that length of time. 



All care should be taken to prevent fresh fields becoming 

 infected. For this purpose all diseased plants should be 

 burned on the field where they are grown, and tools used on 

 an infected field should be cleaned. None of the diseased 

 tobacco should be mixed with manure or compost heaps. 



It is to be hoped that this disease will not appear in 

 tobacco grown in the West Indies, but if it does, prompt 

 efforts on the lines suggested above should be made to 

 exterminate it. 



English Potato. 



The diseases of this plant are not of so great interest to 

 West Indians as are those described above. Still a short 

 account of a disease which is widely distributed in the 

 United States may be of interest. It is fully described in 

 Bulletin No. 55 of the Bureau of Plant Industry (United 

 States Dei»artment of Agriculture) by Messrs. Erwin F. 

 Smith and Deane B. Swingle. 



This disease is also due to a Fusarium. The fungus 

 attacks mainly the underground stems and roots and is 

 characterized by a l)lackening of the vascular bundles. 



The disease in the tubers nearly always begins at the 

 stem end and is shown Ijy a browning or blackening of the 

 vascular bundles. Externally the tubers now appear quite 

 sound. The dark stain finally grows on to the eye end of the 

 tuber. The parenchyma may remain sound and white for some 

 time, or it may become yellowish and finally shrivelled, 

 greyish brown and hard, or it may break down with other 

 soft rots. The disease contiimes in stored potatos, especially 

 when they are stored in warm rooms. As precautionary 

 measures, no diseased tubers should be planted ; they should 

 be used early in the season ; they should not be thrown on the 

 compost heap ; infected land should be rested for some years. 



Spanish Needle. In a paper in the Bulletin of the 

 Jamaica Dejxirtinent of Agriculture on 'Jamaica Fodders,' 

 to which reference was made in the Agricultural News 

 (Vol. II, p. 409), Mr. Cousins gives the results of an analysis 

 of Spanish needle (Bidens leucantha) and mentions that it 

 has slight purgative projierties and is useful as a medicine 

 for horses in poor condition or suffering from worms. In his 

 note on the use of thymol for worms in horses (see Agri- 

 cultural N'ews, Vol. Ill, p. 157) he recommends that a feed 

 of Spanish needle be given after the administration of the 

 thymol. Again, we find ilr. Barclay in the note on rabbit 

 diseases published on p. 203 of this issue, recommending this 

 plant for feeding to rabbits suffering from constipation or 

 diseased liver. Stock owners would therefore do well to make 

 use of this very common plant. 



