TEAR-STAIX CF CITRUS FRUITS. 6 



The publications cited contain practically all the more important 

 references to wither-tip tear-stain in Florida or near-by sections where 

 the round orange and grapefruit are grown in large quantities, and no 

 presentation of actual experimental data is made therein on which the 

 fungus theory regarding the cause of tear-stain is based. However, 

 it can not be denied that this theory, first stated by Rolfs, is so plaus- 

 ible that it has been accepted readily without the support of published 

 experimental data. It was not until results very strikingly incon- 

 sistent with this theory appeared in experimental spraying tests that 

 its validity was questioned, and this has led to a thorough investiga- 

 tion of the causation of the type of injury commonly known in Florida 

 as "wither-tip tear-stain." The evidence presented in this bulletin 

 indicates that Colletotrichum gloeosporioides is not responsible for 

 tear staining in Florida. If this fungus ever produces such an 

 effect, it must be extremely rare in that section. 



SPRAYING EXPERIMENTS. 



During the season of 1917, in connection with spraying experiments 

 which were conducted in a bearing grapefruit grove for the control of 

 citrus scab, it was observed that tear staining was almost entirely 

 absent from those plats that received several applications of lime- 

 sulphur solution, though it was quite prevalent where Bordeaux 

 mixture had been applied during the scab-spraying season. Since 

 this first observation, many similar manifestations of the lack of 

 control of tear-stain by copper sprays have appeared in the experi- 

 mental plats. Such a failure has been proportional to the severity 

 of rust-mite attack. 



Ordinarily the scab-spraying season in Florida begins in February 

 when the spring growth starts and extends over a period of two or 

 three months. It is followed rather closely by the period of very 

 severe attack by rust mites. The latter are usually most abundant 

 during May and June and are readily controlled by two or three appli- 

 cations of lime-sulphur solution diluted 1 to 66. With this explana- 

 tion the data in Table I can be readily interpreted. 



In general, the results of this spraying experiment show (1) that 

 tear-stain was controlled on plats 3 and 5, which received applications 

 of lime-sulphur solution shortly before the period of maximum abun- 

 dance of rust mites; (2) that tear-stain was materially reduced on 

 plat 4, which received applications of lime-sulphur solution consid- 

 erably in advance of the period of maximum numbers of rust mites; 

 (3) that tear-stain was not reduced on plats 1 and 2, which received 

 spray applications of copper mixtures. Assuming that tear-stain is 

 caused by a species of Colletotrichum or other fungus, it would be 

 reasonable to expect that plats 1 and 2 would show at least as good 

 control as plat 4. The fact that control of tear-stain was so closely 



