THE MONTHLY BULLETIN. 333 



THE USE OF THE FUNGUS ISARIA FOR THE CONTROL 



OF THE BLACK SCALE.* 



By H. J. QUATLE and A. R. Tylor, Citrus Experiment Station, Riverside, California. 



Considerable interest, through commercial exploitation, has been 

 aroused recenth' in the use of a fungus for the control of the black scale 

 on citrus trees. The fungus in question, which belongs to the genus 

 Isaria, represents no new discovery, in spite of the fact that many 

 people have been led to believe the contrary. "While it lias been brought 

 prominently to the attention of growers only during the past year or 

 two, it was observed by the senior writer in the Carpinteria district as 

 early as 1908, and has no doubt been present in naturally favorable 

 situations for many years. The fungus and its effect on the black 

 scale as observed in 1908, are illustrated in Bulletin No. 223 of the 

 California Experiment Station, which was issued in 1911. 



Because of the interest that has been manifested in the supposed 

 effectiveness of the fungus Isaria by some growers, the Citrus Experi- 

 ment Station undertook to carry on experimental tests with the fungus, 

 the results of Avhich are given below. The writers are indebted to 

 Professor H. S. Fawcett for pure cultures of the Isaria, and also for 

 suggestions and aid in the work. 



FIELD EXPERIMENTS. 



Experiment No. 1, February 3, 1915. 



A pure culture of the Isaria fungus was cut into small bits, ground 

 with the fingers in water, and after considerable shaking and agitation 

 the coarse particles were screened out. The cloudy solution obtained in 

 this way, containing spores and pieces of hypha; of tlie fungus, was 

 transferred to an atomizer and sprayed on to three branches of mature 

 Eureka lemon trees. These trees were heavily infested with the black 

 scale and the tAvigs selected were fair representatives with respect to 

 infestation. Examination of these scales showed that 81 per cent were 

 alive at the time of beginning the experiment. 



On February 18th, examination of the sprayed twigs showed the 

 scale to be in good condition and no trace of the fungus was present. 

 On J\larch 12th, one spraA^ed twig from each tree and a check twig 

 from an unsprayed tree were cut for examination with the following 

 result : 



Sprayed twigs Clieck twigs 



Number of scales examined 722 277 



Percentage alive 85 SO 



On March 29th the second examination was made with the following 

 result : - 



Sprayed twigs Check twigs 



Number of scales examined 426 361 



Percentage alive 89 86 



♦Paper No. 12. Citrus Experiment Station, College of Agriculture, University of 

 California, Riverside, California. 



