94 



THE AGRICULTURAL NEW?. 



M.a 13, 1915 



FUNGUS NOTES. 



INVESTIGATION OF CITRUS DISEASES 

 IN FLORIDA. 



Mycological investigations in Florida during I'.MI were 

 described in the Agri ultural Newt, Vol. XII, p. 398. The 

 present article, based on the Report of the Agricultural 

 Experiment Station, for the year ending June 30, 1913, 

 reviews a continuation of the work previously recorded. 



Hitherto in Florida, the work of principal interest to 

 i West [ndies has been the campaign against the Citrus 

 white i1\ let ritri), bj spraying with the spores of 



entomogenous fungi parallel with the campaign against the 

 froghopper in Trinidad. This work h..- been continued in 

 Florida with interesting results, which will be given later in 

 this article. As well as this work just mentioned, the reporl 

 under review refers to several new lines of investigation. 

 The first one deals with the control of die-back by Bordeaux 

 mixture 



Die-back oi Citrus trees is a malady supposed to be due 

 to physiological causes. The reason for testing the effect 

 of Bordeaux depended on the circumstance that there is 

 evidence from practice and experiment, that this spray has 

 a stimulating effect on plant tissue* The tree, were sprayed 

 thoroughly with Bordeaux of 5:5:50 strength, twice during 

 the spring of 1912. Within ten days after spraying with 

 Bordeaux mixture, the trees wen' sprayed thoroughly with an 

 ecticide in order to control the scale insects, which 

 experience has taught will greatly increase in numbers 

 alter the use of copper sprays on account of the killing 

 of the entomogenous fungi, which hold the scale insects 

 in control. On the whole, the treatment was found to be 

 effective: Bordeaux mixture appears to be a useful spraj 

 f or the control of die Lack: but its benefits were some 

 what hidden by a decrease of the disease due to natural 

 causes. The effect of the insecticide used after the Bordeaux 

 is marked by the lack oi anj great increase of scale over that 

 existing before the experiment was started. 



Turning to another section of the report, we find an 



mtol hi interesting piece ot vyprkon the gumming of 



Citrus produced bj chemicals. It is worthy of observation 

 that in the die-back investigation, the stimulating effect of 



poisons in -small doses was the lerlying principle; in the 



e of the effect of chemicals on gumming, it is the morbid 

 effect of poisons that is taken into account. To continue, 

 scune twentj eight different organic and inorganic chemicals 

 were placed beneath the bark, oi in holes in the trunk, or 

 were painted on the surface of the bark. The production of 

 gum was coincident with the injury caused bj the 

 chemical. The most copious production of gum was caused 



bj copper sulphi 1 the other salts of the hea^ \ metals 



interesting in view of the beneficial effects of copper in 

 the form oi Bordeaux mixture and the injury extended 



lr the point ol it ertion in the bud or stock, to the upper 



branches. The injurj caused by the other compounds was 



confined to the regi f insertion. The amount oi gum 



formed in this case was small im production wa 



ociated with the pla bet al injury. En all ca 



the gum Was of th' l "' 1 '- 



i ..,,,,_ now to the campai ;ainst Citrus '• 



(see Agricultural Ntws, Vol. \ll, p. 398) tic general results 



■ ,.,i undei review were about tic -aim as 

 repi 1 9 1 2. It ha i furl her esl ver, 



thai moist wi ditions markedly increase the efficit 



of the MicrOCera fungUft On tilt -Una hand, mere wetting 



of the leaves with water free from spores had no effeel on 

 the increase oi Microcera. Tic- following summary of th 

 investigation is reproduced from the reporl in full: — 



'1. Natural mortalitj of white fly is caused mostlj bj 

 Microcera ( Fusai iura > as show n bj : 



'(a) The bodies of .98 per cent, of such natural mortal 

 ity victims, or pieces thereof, yielded Microcera when grown 

 in suitable culture media: 28 per cent, being pure colonies ot 

 Microcera. 



•iin No other fungus was obtained even hall 

 frequently. 



'(c) Except in very unfavourable weather, spraying 



with a suspensi f the spores ol Me n cera caused a marked 



rise in the natural mortality. Microcera could always be 

 recovered from these dead I u vae. 



'(d) Spraying or dipping with a suspension ol spon 

 from a pure culture on sweet potato caused fully as marked 



an effect as similar Spraying, or dippings in a suspension "I 



victims of natural mortality. 



\e) The period between spraying or dipping and the 

 appearance ol the marked increase in dead larvae corresponds 

 closely with the tine- required for Microcera to develop in 

 artificial medi i. 



'2. It is possible, by spraying with Microcera, toinci 

 natural mortality among white fly, but such increase is only 

 temporary . 



■:; Microcera grow, best 'luring periods ol high humid- 



it\ but not too high temperature. 



•1. It is not as thorough in its work as the brown fungus 



or even the led Aschersonia; that is, it is less virulent. 



•o. It acts much more quickly than either of the others 

 '6. It is so universally present in groves that spraying 

 it alone into tree, is not as important lor the grower as it is 

 to spray the red, and especially tic- brown fungi. NYvertlm 



less, in spraying either the red or the brown fungus, it is an 

 excellent idea to add Microcera. 



'7. For spraying purposes artificial cultures of Micro 



on sweet potatoes are to be preferred to th.' victim, of natural 



mortality, because a much larger number ot spores gel in sus- 

 pension from artificial culture.' 



The last invi stigation of interest to the West ludie., des 

 cribed in this report, i^ that dealing with Melanose, a malady 

 which affects the leaves, stem,, ami fruit, of nearly all 

 varieties of citrus. It is caused bj Phomopsis citri, Fawcett, 



and occur, in tic \\ est Indies. The results obtained as to the 



effeel oi fungicides in preventing Melanose infection are of 



some considerable importance. The following fungicides v 

 used: (1) lime-sulphur, ("_') Bordeaux mixture. (.'!) amino 

 in... ..! solution of copper carbonate. The first seemed 

 to prevent infection completely, but caused more or less 

 injury to the foliage by burning or scalding the edges 

 of th.' leaves, or by producing yellowish blotches or 

 spots on tic surface. While Bordeaux mixture did not 

 entirel) prevent infection, th.- amount ot spotting was s. 



small as to be eon, id. -red negligible \'" injury to the 



foliage resulted from the use ol Bordeaux mixture. In the 

 i i - of the third fungicide there was some infection, but not 

 enough to be worth considering from a practical point of view 

 In one of the experiments with ammoniacal copper carbonati 

 there resulted .. sligln burning ot the foliag 



[n Concluding this review, attention may be called t. 



an .. .in in the Reporl i lial scab ol .an us becami 



increasingly troublesome during the year. The disease hen 



referred to wa, .fail. tie,, the new canker. 



w. \ 



