Rust Mite

Pests of Field Crops in Southern Africa

RUST MITE

(Acarina: Eriophyidae)

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Text Box: The tomato rust mite (or russet mite), Aculops lycopersici, is a member of a group of minute, worm-like plant-feeding mites which have only two pairs of legs, in contrast to the four pairs characteristic of mites. The Eriophyidae contain many mite pests which are either free-living on the plant surface, such as this one, or which live in galls, such as the species which causes aloe galls. The russett mite is about 0.2 mm long, 0.07 mm broad, spindle-shaped and yellowish in colour. The mites are found on both surfaces of the leaves feeding amongst the leaf hairs, but are more or less impossible to see with the naked eye, and are usually recognised by the symptoms of damage. TOP

Text Box: Tomato is the main host for this pest, but infestations have been recorded on other solanaceous plants such as potato, brinjal and cape gooseberry. It is likely that solanaceous weeds are also among its hosts. TOP

Text Box: The injury caused by the mite gives it its common name. Feeding on the surface of the plant produces a bronzed or russetted appearance on both stems and leaves and superficial cracking of the tissue. Typically the symptoms first appear on the lower portions of the plant, and as the affected foliage dries up, the infestation moves upwards. Eventually death of the whole plant can result. Crop losses are mostly caused when older plants are attacked, in which case severe defoliation will result in the fruit becoming sun-scorched. Although the pest has not often been recorded in recent years, it remains a potentially serious pest, especially because of the difficulty in diagnosing it. Overcrowding of plants seems to encourage the mites. TOP

Text Box: The life cycle of this cosmopolitan pest is very short. Development from egg to adult through two nymphal stages is completed in less than a week. From records of infestations, it seems that the build-up of the population begins in about August and reaches a peak in December. The numbers then seem to decline, probably as a result of the rains. In hot, low-lying areas, populations can apparently build up again after the rains come to a halt, from March to May. TOP

Text Box: This pest can be found early in the growing season. Being so small, the mites can only cover very small distances by crawling and they are probably spread mainly by people moving through the crop for cultivation and picking. The most commonly used method of control is by the application of wettable sulphur applied on a weekly basis. However, care must be taken not to spray with this product when temperatures are too high as the sulphur can cause scorching of the plants. More conventional acaricides such as dicofol have also been used with success, but since both of these products are contact acaricides, good spray coverage of both upper and lower leaf surfaces must be achieved. Residues from an infested crop should be destroyed after harvesting, lands should be kept clear of weeds and new plantings of tomatoes should not be nearby. TOP

Rust mite damage to tomato plant. (Photo: J K Clarke, US Statewide IPM project, Univ. California.)

Rust mite close up. (Photo: J K Clarke, US Statewide IPM project, Univ. California.)