CITRUS scab: its cause AISTD CONTROL. 31 



fungi. So effective are these fungi in the control of certain insect 

 pests that there are numerous orchards which bear plentiful crops 

 of excellent fruit without the aid of sprays. About 12 species of 

 entomogenous fungi are recognized in Florida citrus orchards. The 

 earliest forms begin growth about the 1st of May, and the later 

 forms are active until late fall or winter. 



It is true that the time for spraying against scab on grapefruit 

 usually has passed before the entomogenous fungi become active. 

 It is also true that any fungicide especially effective in scab con- 

 trol is likely to persist on the sprayed parts for a considerable time 

 after the period of scab infection has passed. Further, any fungi- 

 cide effective against scab is hkely to be very harmful to the entomog- 

 enous fungi. Therefore when an effective, lasting spray is applied 

 to control the scab fungus a corresponding control of entomogenous 

 fungi is most likely to occur, and this would result in an enormous 

 increase of insect pests unless drastic measures are taken to check 

 them. 



These entomogenous fungi seem to thrive best under local con- 

 ditions which are especially favorable for citrus scab. For example, 

 in those rather moist localities where natural control of insect pests 

 is most pronounced attacks from citrus scab are usually severe. 



Citrus scab tends to vary greatly from year to year and section 

 to section. Even in a given locality it varies a great deal, and the 

 fact that an orchard is affected seriously with citrus scab is by no 

 means strong evidence that the same property will be even lightly 

 affected the following year. 



Nevertheless, there are localities where citrus scab is regularly 

 serious, others where the disease is usually moderately prevalent, 

 and still others which are attacked only during years especially 

 favorable for citrus-scab development. For the sake of economy 

 these thi'ee types of locaUties should not have the same spray schedule 

 for the control of citrus scab. A spray program which would list 

 the least number of applications necessary to produce clean fruit 

 in localities where citrus scab is constantly serious would be un- 

 necessarily expensive in time consumed and materials used where 

 the disease occurs only during years especially favorable for scab 

 development. 



On the other hand, one or two applications of lime-sulphur solu- 

 tion, though it is a weak, short-lived fungicide, made during the 

 scab season is money well invested, even if scab does not occur, for 

 the reason that such applications practically eliminate red spiders 

 and greatly reduce rust-mite injury. 



The judicious selection of the spray material for use in a citrus 

 orchard is by no means an easy task, because all are not equally 

 effective against scab, and certain of them are likely to be followed 



