10 BULLETIN 924, TJ. S. DEPARTMENT OF AGRICULTURE. 



which had been isolated from an injured grapefruit leaf. The 

 spores were washed off the twigs and mixed with those from the 

 culture tubes. This wash water, which was clouded with fresh viable 

 spores, was used in saturating wads of absorbent cotton, which in 

 turn were placed on the fruit. The inoculated fruit was covered 

 with two or three layers of waxed paper for 48 hours. At the 

 expiration of this time the paper and wet cotton were removed and 

 the fruit left unprotected. To serve the purpose of a control, other 

 fruits were similarly treated, except that the cotton was wetted 

 with sterile water. These inoculations gave negative results. 



Similar inoculation tests were made during the fall of 1919, using 

 as inoculum a mixture of a number of strains of Colletotrichum gloeo- 

 sporioides isolated from typical tear stains on grapefruit and from 

 dead grapefruit twigs, as follows: 



On October 20, 1919, on almost fully grown grapefruit; on October 27, on grapefruit 

 showing faint yellowing ; on November 7 , on grapefruit approximately one-half colored ; 

 on November 15, on grapefruit almost fully colored; and on December 3, on mature 

 grapefruit. This test was repeated during the late spring, summer, and fall of 1920, 

 using mixed inoculum from the same strains of Colletotrichum gloeosporioid.es. Inocu- 

 lations were made on May 15, on grapefruit averaging 1 inch in diameter; on May 31, 

 on grapefruit averaging \\ inches in diameter; on June 15, on grapefruit averaging 

 If inches in diameter; on June 30, on grapefruit averaging 2-fg inches in diameter; 

 on July 15, on grapefruit averaging 2h inches in diameter; on July 30, on grapefruit 

 averaging 3 inches in diameter; and on November 1 and 6, on grapefruit just be- 

 ginning to color. 



The results of all these tests were negative. Not the slightest 

 symptom of tear-stain in any of the fruits inoculated during 1919 

 could be detected as late as February, 1920, when the crop was har- 

 vested. The fruit inoculated during 1920 was free from tear-stain 

 when final observations were made in November. 



Observations were made to determine the frequency of association 

 of tear-stain with dead twigs that might harbor Colletotrichum or 

 other fungi. Unsprayed groves with more than the average propor- 

 tion of dead wood present w T ere examined carefully during the past 

 four years. Among the properties inspected in Florida 4 are in Lee 

 County, 10 in Polk County, 2 in Hillsboro County, 3 in Pinellas 

 County, 3 in Osceola County, 10 in Orange County, 2 in Volusia 

 County, 4 in Brevard County, 3 in St. Lucie County, and 4 in Dade 

 County. The data obtained indicate that dead twigs, spurs, etc., are 

 found immediately over not more than 10 per cent of the tear-stained 

 fruit, and that in damp, densely shaded, low-hammock properties, 

 where trees have an unusually large number of dead twigs and where 

 environmental factors would appear to be especially favorable for the 

 development of fungi, tear-stained fruits are very seldom found. On 

 the other hand, tear-stain is most abundant in higher and drier lo- 

 cations where light and moisture favor the greatest rust-mite 

 development. 



