516 INSECTS AFFECTING VEGETATION 



Russeting Due to Rust Mites. Russeting of the citrus fruits 

 may be produced by one of several agents; rust mites (Eriophyes 

 oleivorus), withertip fungus (Colletotrichum glocosporioides) , and 

 melanose. The last-named does not properly belong among the 

 russeting, but frequently when fruits are affected by melanose in a 

 peculiar form with the specks exceedingly minute and generally dis- 

 tributed, they are placed among the russets. The rust mite is not an 

 insect, but is more closely related to the spider mites. 



Rust-mite russeting is the most general affection of Florida 

 citrus fruits. It occurs on all varieties of grapefruit and oranges, in- 

 cluding the sour orange and even the bitter sweet (though these two 

 varieties are nearly free from it.) W nen russeting is caused by rust 

 mites, the appearance of the fruit varies from the least tinge of dark- 

 ening to a nearly pitch black, with all intermediate grades. As a 

 rule, the russeting occurs on the side toward the light, shading off to 

 the side of the fruit next the interior of the tree. Not infrequently 

 the side of the fruit exposed to full mid-day sunlight is also free 

 from russeting. Fruit more or less shaded is likely to be rather 

 evenly russeted. In dense shade the fruit is nearly always bright. 



The migration of the rust mite from the leaves to the fruit 

 does not normally occur before the latter part of April, and usually 

 not until the middle of May. Usually much damage has been done 

 before the grower is aware that the mites are present. The multipli- 

 cation of the mites is very rapid, and in the course of two or three 

 weeks nearly all the fruit of a grove may be affected. 



Moist weather, or any condition that induces a high humidity, 

 is likely to cause partial or complete destruction of the mites. Dry 

 weather and conditions that induce low humidity are favorable to 

 the development of the mites. Some hammock groves are notably 

 free from russeting, while many pine land-groves are noted for the 

 production of russets. 



Rust-mite russeting may be distinguished from other forms by 

 the skin being smooth and frequently shiny ; while withertip russet- 

 ing is dull-colored as a rule and rather rough to the feel. Melanose 

 russeting can always be distinguished by the discoloration occurring 

 in sharply defined dots. Any two or even all three may occur to- 

 gether on the same fruit. Much confusion and disappointment 

 have arisen in recent years because many have assumed that all rus- 

 seting was due to the rust mites, which is quite contrary to the facts. 



Sulphur and its compounds are the substances that form the 

 remedies par excellence for the destruction of rust mites and other 

 pests belonging to this group of animals. Dry sulphur, or sulphur 

 and lime mixed in equal parts may be applied with an air gun. 

 This is a cheap and more or less satisfactory remedy. The soda- 

 sulphur and lime-sulphur compounds have long been used and are 

 still among the most efficient remedies. The self-boiled lime and 

 sulphur should also prove an excellent remedy, but has not been 

 tested by the writer. In using the lime sulphur solution or the soda- 



