CITRUS SCAB: ITS CAUSE AND CONTROL. 31 
fun^i. 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 likely 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 three types of localities 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 tusk, because all arc not equally 
effective against scab, and certain of them are likely to be followed 
