632 



Leefmans (S.)- De Cassave-Mijt. [The Cassava Mite.] — Meded. van 

 het Laboratorium voor Plantenziekten, no. 14, Dept. van Landhouw, 

 Nijverheid en Handel, Buitenzorg, 1915, 35 pp., 3 plates. 



In 1906 the cassava mite was reported from a large cassava estate 

 in East Java on the slopes of the volcano, Kloet. According to 

 Dr. P. J. S. Cramer, of the Department of Agriculture, this Telranychus 

 is distinct from both T. exsiccator, Zehntner, the sugar-cane mite, and 

 T. biocidatus, Wood Mason, the tea mite. Planting another crop, on 

 which red spider could not live, to alternate with cassava, and thus 

 limit the spread of the pest, was advised, but technical reasons prevented 

 this recommendation from being followed. For a long time nothing 

 was done but stripping the leaves of the plants attacked. In 1912 

 the question was taken up again. The damage caused is very 

 characteristic. Yellow spots appear on the leaf near the stem, and 

 the leaf ultimately becomes entirely yellow and drops. The mites 

 live under the leaves and are rarely, if ever, found on the upper surface. 

 The cassava mite is a diy monsoon pest. A long dry period, heavy 

 winds and the effects of the mite unite to make the leaves drop over 

 large areas, causing considerable losses, especially as the plants, after 

 being attacked repeatedly, often die. During the rains, the cassava 

 mite causes no damage of any importance, though not entirely absent. 



The author considers the species concerned to be Tetranyclms 

 bimaculatus, Harvey. The pale yellow eggs are laid on the underside 

 of the leaves, generally near the veins. They hatch after four or five 

 days. The freshly emerged spider-mites are pale yellow ; they reach 

 maturity in 10 or 11 days. T. bimaculatus, Harvey, is now found in 

 Java on cassava, Ricinus communis. Cinchona and Clitoria and on 

 many weeds and grasses. Immune varieties of the sweet cassava 

 are unknown there. Experiments proved that the mites spread 

 principally by travelling from plant to plant and are assisted by the 

 wind, especially when attacked leaves, bearing many mites and their 

 eggs, drop to the ground and are blown away. Dispersal may also 

 be assisted by the labourers, who convey the mites in their clothing. 

 Natural enemies include Coccinellids and a predaceous yellow mite, 

 the latter probably not being of importance. Experiments were 

 tried in conveying beneficial Coccinellids from the rice fields, where 

 they occurred in great numbers, to the cassava, but they could not 

 be induced to remain there. About 50 insecticides were tried. The 

 best was lime-sulphur, 5 per cent., 28° Be., to which 1 litre of potash 

 resin soap was added for every 15 litres of lime-sulphur (1 litre of potash 

 resin soap was made by boiling 33 grms. resin and 5 grms. caustic 

 potash in 1 litre of water). This insecticide killed all the mites which it 

 touched, as well as 97-4 per cent, of the eggs. Lack of water however 

 prevented its use on a large scale, and it is also rather expensive. Small 

 experiments with finely powdered sulphur gave favourable results, but 

 on a bigger scale it was not satisfactory, as one month after the applica- 

 tion the plants were again rather badly attacked. The only method 

 giving generally good results, if applied in time, is the stripping and 

 burning of the attacked leaves. This method involves, however, con- 

 siderable loss and is therefore only advisable for small areas in order to 

 prevent the spread of the pest. The long diy periods in the locality in 

 question specially favour this pest, and better watered areas with a 

 regular rainfall should be chosen for cassava culture. 



