January 2001. Red spider mites are often a problem on taro, especially during dry times. The question asked was how to control mites infesting breeding blocks in a screen house in Samoa. Malathion was being used as there was no alternatives available in the country. However, when it was used at the rate of 4 ml/l, it almost killed the plants and it had little effect on the mites! They were spreading fast.
PestNet members confirmed that malathion was not a miticide, and will only make the situation worse. Petroleum sprays at 0.5% should be effective, although it may take several applications to bring the infestation under control. Sprays of soapy water under light pressure are likely to be effective too; they literally wash the mites off the leaves. Light oils, e.g., vegetable oil could also be added to block the mites’ spiracles. In order to prevent similar outbreaks, it was suggested that the leaves be daily sprayed with water.
Three recommendations were provided by the Northern Territory of Australia to contain the outbreak:
- Miticides: fenbutatin oxide (Torque) and propargite (Omite); this is assuming that neither chemical is used widely in Samoa, if they were, there may already be resistance to these miticides.
- The TSM predator, Phytoseiulus persimilis, which is highly effective during the dry season of the NT. The predatory mite is released at the first detection of two-spotted mite. However, a regular a supply of the predatory mite will be needed as it does not do well under high humidity.
- Sprays of petroleum spray oil, (e.g., DC Tron plus) at relatively low rates, 0.3 to 0.5%. Weekly sprays at these rates will suppress TSM, but spraying needs to start when the populations are very low. From the description, that might be too late. It is best to monitor the crops and start spraying as soon as TSM is seen.
- Potassium soap/neem oil. Some growers have had success with this product. It consists of neem oil that has been treated with potassium hydroxide, and it appears to be effective.
PEQ staff in Australia also provided the following miticides as being worthy of testing:
||Use with miticide
||Use with Torque
||Use in cooler weather
Like all miticides, ensure different chemicals are use to minimise resistance development.
Kethane is an older product; another is Rogor (dimethoate), which is systemic and also an insecticide. In Australia, Kelthane can be bought for home garden use as a product containing 70 g/l dicofol, and is recommended as a 6 ml per litre spray. Rogor is also available for home garden use as a product containing 300 g/l dimethoate, and is recommended as a 1 ml/litre spray.
It is also suggested that the mite is identified. Cut out pieces of leaf and place immediately in 70% alcohol.