It Pays to Control Rust Mite

Abstract

Strange to say, the rust mite is not an insect but is more closely related to spiders. It is a near kin of the itch mite, bugs, red spiders, and cattle ticks. It feeds on all new green growth of trees: leaves, fruit and twigs. It seems to live on juices taken from trees, particularly the oil. However, if these mites consumed all the oil from the glands they open we would have no real rusty fruit. In fact, the rusty appearance of fruit, leaves and twigs is due to the oil oozing from glands that had been tapped by the mites. The oil flowing from the punctured glands spreads out more or less over the rind of the fruit and during nights of heavy dew or light showers may run down the sides of the fruit in narrow bands; the exposure of these thin layers of oil to the air causes the oil to break down or oxidize and change to a dark color, thus resulting in rust and where it had run down the fruit in streaks to tearstaining. There is another effect that the exuding oil has on young fruit and other newly developed parts of trees that should be mentioned in this connection. In 1914 and 1915, I punctured a large number of oil glands on newly hardened young twigs and halfgrown oranges with a very fine pointed needle under a lens. The punctured areas were marked and kept under observation during some weeks. Small amounts of oil escaped from each pricked oil sack and spread over tiny spots and areas, the shape of which depended upon the. action of gravity on the escaping oil. After a few days the distribution of the oil was definitely and clearly shown by brown spots of the exact size and shape of the oil-covered area. In order to make a further test of the effects of orange oil on the epidermal tissues of fruit, leaves and twigs of orange and grapefruit, a small quantity of this oil was obtained and applied with an atomizer so as to cover the surface with tiny spots of oil; in other cases the application was continued until the oil spots became so numerous and close together that they eventually touched and thus covered considerable areas completely with a continuous film of orange oil. The result was interesting in that in case of the light applications every point, formerly occupied by oil-dust particles delivered by 33