14: 



THE AGEICULTUEAL NEWS. 



May 5, 1917. 



PLANT DISEASES, 



CITRUS DISEASES IN CUBA. 



The difficulties which undoubtedly existed, to students 

 •o! citrus literature, in comparing; the citius diseases of Florida 

 and (.'alifornia with each other and with those of the West 

 Indies, have been considerably le.-isened by the publication 

 of a paper by H. S. Fawcett in which .--uch a comparison is 

 -made as a result of studies in the States referred to and of a 

 visit to Cuba and the Isle of I'ines. (Bulletin 262, University 

 ■of California Agricultural Experiment Station.) The author 

 points out that in some cases different names are apparently 

 teing used for the same disease, and in other cases, the same 

 SDnme is being u.^ed for different diseases. 



A.s being of most direct interest to West Indian growers, 

 the author's account of the diseases met with in Cuba is here 

 Teproduced. 



Hal di yoni.ma or 'foot r^il', as it typically occurs in 

 riorida on old seedling orange trees, and a few cases of 

 3)sorosis (California scaly bark) were seen. Diplodia gumm- 

 ing, due to Z))'/)Zf«f/'( vi'tahiuis, in which fair sized branches 

 •were killed back was probably the most common of the gum 

 diseases. It was seen in nearly ever}' locality visited. This 

 Tnay pos.-^ibly be the disea>;e spoken of under 'twig gummosis' 

 fcy W, T. Hcrne in Bulletin 9 of the Cuban Experiment 

 -Station. Grapefruit (pomelo) trees seemed especially sus- 

 ceptible to this trouble. The same fungus was also found in 

 nearly every locality in decaying pomelo fruits. A gum 

 .disease on the trunks of lemon trees was also fairly common, 

 "but it appeared to take a different form from either the 

 J'ythio.cysitisox Botrytis gam\ao?Ai in California or foot rot in 

 Tlorida. There appeared to be a large amount of exudation 

 of gutn with a small amount of killing of bark. The outer 

 'Tjark was killed ahead of the inner, somewhat like the 

 "Botiytis form, but the Botrytis fungus was not found in it 



The mo.st serious form of gum disease in I'uba common 

 on heavy soils, appeared to be the Pythiac>/$tis gummosis. 

 lieginning at the base of the trunk the bark was killed for 

 *ome distance above the ground with the exudation of consider- 

 -able gum. This form in most cases resembled closely the 

 Pythiacysiis (brown rot) gummosis, as it occurs in California 

 on heavy soils. It is strongly .su.spected that this may be 

 -only one form of mal di gonima. The bark was killed rapidly 

 =clear through to the wood and had the characteristic 

 odour of bark killed by Pythiacystis; from specimens of suih 

 bark from a grapefruit grove at Santiago de las \'egas, 

 cultures of Ppthiacystis riiropJuhora were obtained. As 

 ii culture of Pythiacystis was also obtained from similar 

 specimens on the Isle of Pines and also at Palmetto, Florida, 

 it would seem that this fungus is the causal agent in that 

 ;j)articular type of gummo.sis there as well as in California. 



Scab or Verrucosis i (Jladosporium citri). Probably next 

 dn importance to the gum diseases, was scab, especially on 

 ^'rapefruit. During yi^ars when the moisture and growth 

 jconditions are favourable for infection by the scab fungus. 

 SI great deal of trouble is experienced from this disease. It 

 ^ittacks the young fruits, just as they are growing most 

 "Jivpidly. The off bloom or •.June bloom' fruit is most apt tn 

 In be infected seriously. Thr- leaves also may be contorted 



and warped out of shape by it. The copper sprays (Bordeaux 

 and ammoniacal copper carbonate) have been used successfully 

 in preventing it, but the increa.se of .scale insects due to 

 killing off the fungus parasites of the insects is so rapid 

 that many growers hesitate to spray with these copper 

 fungicides. Lime sulphur is being tried out and is 

 reported to have given good results. 



Wither tip of Limes {Gloeonporhim Linutticolum).. 

 Withertip of lime trees, the same as occurs in South Florida, 

 appeared to be a prevalent and serious disease throughout 

 the Island. It blights the new growth as it comes out and 

 interferes materially with the setting of young lime fruits. 

 This is the disease which Jlr, liny Clausen of the University 

 of California, determined to be due to a fungus resembling 

 but apparently '_uite distinct from the CoUetotrichum 

 gloecspoiiouhs, which is associated with withertip of other 

 varieties of citrus in both Florida and California. 



Blossom eml rot of Persian limes. Wherever the 

 Persian limes were found, there was a certain amount of 

 a firm rot at the 'iilossom' or stylar end of the fruits. This 

 appears to be the same as has been observed in Florida and 

 in one case in California. It appears first as a whitish, 

 sunken patch around the stylar end. This patch remains 

 firm and does not, as a rule, soften much as in some other 

 kinds of decay. The cause is as yet unknown. It would 

 appear to be due to an organism of some kind. A fungus 

 resembling Colletotrichuniffloeosporioidesvias found commonly 

 in the spots, but was not determined to be the cause of the 

 trouble 



Diplodia rot ( Diplodin nalahnsis). A decay, especially 

 of grapefruit, which begins at the stem end and slowly rots 

 the fruit was quite common. (The 'stem end rot' due to 

 Phomopsis ct<ri was not seen,) Cultures made from such 

 fruits at various localities showed the Diplodia fungus to be 

 present. This aside from bhie molds appeared to be the most 

 important decay. The same fungus has alread}- been men- 

 tioned in connexion with the Diplodia gumming in branches. 

 In some places considerable tear streakins, probably due to 

 the withertip fungus, was also seen. 



Leaf Spot, due to an Alga (Mycoidea parasitica). 

 A certain amount of damage appears to be due to a species 

 01 alga attacking the leaves, producing a wart-like growths 

 This is not known to be present on citrus in either Florida or 

 California The damage from any one spot is negligible, but 

 when the leaves become covered with spots they are weakened 

 and fall off. It has not usually been considered serious 

 enough to use any methods of prevention in Cuba. Any 

 fungicide would probably prevent it. 



Dark Greasy Spot ('Black Melanose'), Although the 

 true Melanose appeared to be absent from Cuba and the Isle 

 of Pines, a dark, greisy spot sometimes called in Florida 

 'Black .Melanose', was very common, especially on grapefruit 

 leaves. The writers observation would lead him to say 

 that this dark, greasy spot increases in prevalence and effect, 

 as one passes from the northern to the southern part of 

 Florida, -and is even more prevalent in Cuba and the Isle of 

 Pines. The spots have a dark, slightly raised, greasy 

 appearance, suggestive of a mass of dark grease under 

 a transparent epidermis. Their development on leaves 

 in Cuba is much more definite than in most parts 

 of Florida and would strongly suggest the eff'ect 

 of some organism. This would be suspected even more 

 strongly since the discovery by Mr, H, E. Stevens in Florida, 

 that the true .Melanose is due to P/tomopsis citri, the same 

 fungus as causes stem-end rot. 



