Berger (1937). They found rings of rust on citrus fruit corresponding 

 to the aforementioned semi-shaded areas. 



Citrus rust mite populations are extremely variable from tree to 

 tree and from various parts of the same tree. This variation in popula- 

 tion distribution was substantiated by Osburn and Mathis (1944). 

 Swirski (1962) felt that the recorded discrepancies were due to a lack 

 of knowledge of density and its relationship to time and space. 



Pratt (1957) reported two peaks of infestations annually during the 

 summer months. He attributed this to the number of hours at dew point. 

 Rasmy et al . (1972) was not able to support his correlation to relative 

 humidity, but was able to show a relation to temperature. 



Cultural practices . Cover crops, the cultivation of annual crops 

 in citrus groves, were studied by Osburn and Mathis (1944). They felt 

 cover crops helped maintain a humid condition that supports parasites 

 and especially fungi that attack the citrus rust mite. They were 

 unable to support this hypothesis, finding that cover crops had very 

 little affect on relative humidity, temperature, parasites, and amount 

 of fungi present. However, they did state that clean culture stimulated 

 tree growth and gave an overall impression of a healthier tree. 



The condition of the citrus tree has been suspected of affecting 

 rust mite populations. Hamstead (1957) demonstrated a correlation 

 between rust mite populations and high nitrogen levels in leaves. Leaf 

 age was shown to cause variations in populations (Mohamed, 1964). Muma 

 (1965) attributed fluctuations in population to leaf drop and wind. 



Cultural practices such as hedging or thinning of citrus trees were 

 found by Swirski (1962) to improve conditions for the citrus rust mite. 

 Overhead irrigation was shown to cause a sixfold mite popula- 



