Mites

Mites – an overview:

This page provides an overview of mite pests in vegetable crops. The related tools listed at the end of the page provide detailed information about their identification, damage and management. It is important to be able to identify pests such as mites, and to have unknown species expertly identified so that they can be appropriately managed.

Mites are not insects, but related to spiders. Most adult mites have 8 legs (insects have 6). Mites are a diverse group, with many being plant pests. Others are beneficial, such as the predatory mites Persimilis, Cucumeris and Montdorensis. Pest mites use adapted mouthparts to lacerate plant tissue and suck up the discharged sap. This can cause stippling, or fine speckling, and/or distortion of leaves, and cracks to develop on affected stems. Mites feed on the underside of leaves and breed rapidly in warm weather. Some mites cover plants in webbing for protection from predators while they feed and shelter. Severe infestations can kill plants.

Mite species, hosts, and damage

Mite species	Description	Host vegetable crops	Primary damage
Two-spotted (spider) mite (Tetranychus urticae)	Adults are yellowish-green with two prominent dark spots on the body. Has an orange-red overwintering form.	Most vegetable crops.	Damage first appears as a fine speckling/whitening on the upper side of leaves due to feeding on the underside. Heavily infested leaves become bronzed and dry.
Tomato russet mite (Aculops lycopersici)	Adults are very small (0.2 mm), white to yellow and torpedo-shaped.	Tomato; capsicum; eggplant.	Infestation generally starts low on the plant and spreads upwards. Stems become bronzed and take on a hard appearance, leaf fall occurs, and the skin of the fruit becomes leathery. The flavour of the fruit is also affected.
Broad mite (Polyphagotarsonemus latus)	Adults are barely visible to the naked eye.	Capsicum; tomato; cucurbit vegetables.	Leaves become bronzed, russetted and distorted (cupped downward). Young stem growth may be distorted and stunted. Fruit may be mis-shapen and russetted.
Red-legged earth mite (Halotydeus destructor)	Adults and nymphs have a black, somewhat flattened body and red legs. Spends most of its time on the soil surface, rather than on plant foliage.	Cucurbits; field vegetable crops.	Plant cell and cuticle damage through feeding promotes desiccation, retards photosynthesis, and produces the characteristic silvering that is often mistaken as frost damage. Most damaging to seedlings and in severe cases crops may need re-sowing.
Bean spider mite (Tetranychus ludeni)	Adults are uniformly red.	Most vegetable crops.	Bronzing or whitening of upper leaf surface. Leaves may turn red or yellow, and drop with heavy infestations.

Management

Mites can be difficult to control as the use of broad-spectrum insecticides reduces the number and effectiveness of beneficial insects and mite populations have developed varying degrees of resistance to several pesticides. For most mite species a range of chemical, biological and cultural control methods are available.

Chemical control

Miticides can be used if the pest pressure becomes high. Mites can be difficult to control by chemical means due to short life cycles and resistance to chemicals. Chemical sprays do not kill mite eggs, and so it is important to time sprays when most mites have emerged. Chemical control may not be cost-effective. For current chemical control options, refer to the APVMA website or a commercially available chemical database. Mite problems are often induced by excessive use of insecticides against other pests, which kills the natural enemies of mites, allowing their numbers to increase.

Cultural control

Cultural control methods for mites include weed control, crop rotation, clean fallowing, mixed cropping, trap or border crops, minimising dust, and changes in tillage practices.

Biological control

Having healthy beneficial populations can help keep numbers of pest mites low. There are a number of beneficial predatory mites. Persimilis spider mite is one of the world's most commonly reared natural enemies and feeds on two-spotted mite and bean spider mite. Cucumeris predator mite feeds on broad mites and two-spotted mites. Montdorensis feeds on broad mite and tomato russet mite. A predatory mite, Anystis wallacei, was imported from France to Australia in 1965 for biological control and has been established at some sites where it has caused significant mortality of red-legged earth mites. Its effectiveness is limited by slow dispersal.