DISEASES OF LIME AND OTHER CITRUS TREES 209 



at the base and are situated on a compact black stroma. In 

 cultures the latter species forms a black stromatic pellicle, a 

 feature absent from cultures of the parasite. The conidia are 

 more pointed than those of C. glceosporioides, with less tendency 

 to be constricted in the middle. The conidia when fresh are 

 markedly less granular, with a less distinct nucleus. The 

 measurements of the two fungi are about the same, the conidia of 

 the parasite being 14-18x6-7 microns, the conidiophores 

 20-30 X 5 microns. 



Control. 



A disease of this description could be readily controlled by 

 spraying, were it not that the flushes of new foliage and the 

 blossoming of the lime are liable to be scattered and erratic. 

 There are, however, fairly well-marked times of maximum 

 production, which vary from place to place, but are pretty 

 constant for any particular locality. By spraying at these 

 times it may prove possible to save a paying proportion of the 

 fruit, and it should be noted that it is just as important to save 

 the shoots as the blossom, since it is upon these that the next 

 crop of flowers is formed. 



From information regarding field studies of control made on 

 behalf of the U. S. Department of Agriculture, kindly supplied 

 by H. P. Fulton, it is learned that a careful spray schedule 

 applied at the time of blooming and early setting can be used 

 with success, though whether the crop will justify the expense 

 is doubtful. An early cleaning-up spray before the blossom 

 comes is probably desirable. " The first fruit spray should be 

 made as soon as enough petals have dropped to allow for coating 

 a reasonable setting of fruit. This would be when the bloom is 

 perhaps one-half to one-third advanced. Later spra3^s will 

 depend upon the progress of the bloom and on weather conditions 

 which may favour the disease. In a general way two or three 

 later applications at intervals of one to two weeks are necessary." 



Burgundy or Bordeaux mixtures are the most effective as 

 sprays, but have the disadvantage, where scale insects are con- 

 trolled by fungus parasites, of killing out the latter and so 

 inducing scale infestations. This action is much less marked 

 with lime-sulphur solution, which nevertheless gives satisfactory 

 control of the disease. The best results have been obtained 

 with commercial lime-sulphur diluted at the rate of about one 

 in 30 to one in 40, care being exercised not to use the greater 

 strength when the temperature is high. For this reason spraying 

 is best done in the cool of the morning or evening. The adoption 

 of a copper spray in the first instance, with the use of lime-sulphur 

 for succeeding sprayings, the combination found desirable for 

 citrus scab in Porto Rico, may be the most satisfactory system 

 to adopt. When no trouble is anticipated from scale insects 

 copper sprays may be used throughout. 



