10 



tion increase (Rasmy et al., 1972). Tree planting distances, especially 

 relating to tree crown distances, were related directly to rust mite 

 density (Swirski, 1962). 



Chemical control . Yothers and Mason (1930) gave an account of 

 tobacco and whale-oil soap being used to eliminate the russeting damage. 

 Sulfur was introduced as a miticide, but was found (Speare and Yothers, 

 1924; Griffiths, 1950) detrimental to fungicidal activity by reducing 

 entomopathogenic fungi attacking the citrus rust mite. Scheduled treat- 

 ments were applied in the spring, summer, and the fall. Numerous acari- 

 cides such as chlorobenzilate, ethion, sulfur, and dicofol can be used 

 for control of P^. oleivora (Florida Citrus Spray and Dust Schedule, 

 1977). 



Injury to citrus fruit . Citrus rust mite has been reported to be 

 responsible for three visable types of fruit injury, namely sharkskin, 

 russet, and bronzing (Griffiths and Thompson, 1957; Albrigo and McCoy, 

 1974). McCoy and Albrigo (1974) demonstrated that injury to the sur- 

 face of citrus fruit by P^. oleivora is restricted to epidermal cells. 

 Sharkskin which is found on grapefruit, lemons and limes (Yothers and 

 Mason, 1930; Griffiths and Thompson, 1957) is occasionally found on 

 oranges. This is characterized by severe damage at an early age. 

 Further fruit growth results in cracking of the dead epidermis in pat- 

 ches which may slough off, leaving a smooth injured periderm (Albrigo 

 and McCoy, 1974). Russet damage, which occurs prior to fruit maturity, 

 results in additional fruit growth, which breaks up dead epidermis, and 

 subsequent wound periderm formation beneath the epidermis. The cracks 

 result in an unpolishable rough texture, while the oxidized cell con- 

 tent gives the fruit the rust color (McCoy and Albrigo, 1974). Fruit 



