The two-spotted mite’s Indonesian name is "tungau" and its scientific name is Tetranychus urticae.
Mites are related to spiders. Only the first immature stage called crawlers have six legs. All other stages have eight legs, not six legs like insects.
Actively feeding two-spotted mites are yellow to green with a prominent dark band on each side of the body. Adults are small — about 0.5mm long. Use a 10 times magnifier when looking for them. They usually occur on the lower side of leaves but as an infestation develops, they will feed on both sides of a leaf.
Eggs are spherical with a pearly lustre. Red eyespots are visible through the egg just prior to hatching.
Feeding by two-spotted mites results in leaves becoming mottled yellow or silver. The presence of mites is first noticed by this change in colour to leaves.
If not controlled, mite infestation can be severe. The mites produce webbing and eventually kill the leaves, which turn brown. This leaf loss reduces crop vigour and yield.
In cooler conditions, mites become dormant and are orange. These mites reactivate when warm weather returns. In temperate regions, overwintering commences in autumn and these adults become active again in early spring.
Two-spotted mites feed on a wide variety of crop and ornamental plants and weeds. If infestations are noticed near potato crops, remove any infested weeds.
Mites are most likley to be present in hot weather and can increase in number rapidly.
Two-spotted mites do not have wings but in windy conditions can be blown into crops. Also, because dust interferes with natural predators, crop edges are more likely to be infested. Therefore when monitoring, pay attention to crop edges.
If mottled leaves are seen during regular crop monitoring, check leaves with a 10 times magnifier to confirm whether two-spotted mites are the cause.
When monitoring for mites, also check whether their natural enemies are present. If they are present and over successive monitoring times are increasing, they may control the mite infestation. The main natural control agents of two-spotted mite include the predators stethorus beetle, six-spotted thrips and predatory mites.
If no natural control agents are seen and more than 20% of leaves are affected by two-spotted mites, a miticide should be applied.
Most miticides do not kill eggs, therefore a follow-up spray 7–10 days later is often required to control new hatchings.
Funding for this work to support Indonesian potato farmers and WA seed potato exports was provided by ACIAR (the Australian Centre for International Agricultural Research) and the Department of Agriculture and Food, Western Australia.