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C. carinatus causes a bronzing or purple discolouration of infested leaves, hence the common name ‘rust mite’ (Mamikonyan, 1935; Anon., 2014). This is more apparent on the leaf margins (Shiao, 1976). Infested leaves also have a ‘dusty’ appearance due to the cast skins of the mites and the residue of ‘mite wax’ on the leaf surface (Anon., 2014). Leaves attacked by the mites turn completely brown and dry up, and defoliation occurs in heavy infestations (Shiao, 1976; Vazquez, 1991). The mites usually attack older leaves and show a preference for the upper surface, especially along the midrib and margins (Light, 1927).
Early Warning Systems
Due to the fact that mites (especially the eggs) can be cryptic on plant parts and therefore pose a risk of accidental introduction in the plant trade, it is important to have measures in place to counteract accidental introduction. For example, in Kenya, the importation of any plant material is subject to strict specified conditions. Procedures include having suitable available information on the plant material to evaluate the pest risk of potential invasives. Regulations ensure that plant materials are imported and exported with appropriate permits and phytosanitary certificates. The authority is in place to treat of destroy infested plants or plant products (IPPC Secretariat, 2005).
In Kenya, inspections are carried out at international airports, sea ports and borders. Most border control points are located in the south and west, given the considerable trade in plant material with Uganda and Tanzania (IPPC Secretariat, 2005).
C. carinatus was introduced into Kenya in the 1976 and caused a reduction in tea leaf production (IPPC Secretariat, 2005). Public awareness of has been raised by, for example: publishing procedures on plant import requirements in the print media; holding public seminars at entry points; and preparing and distributing pamphlets, brochures and annual reports (IPPC Secretariat, 2005).
Cultural Control and Sanitary Measures
Rau (1965) stressed the importance of providing shade, carrying out late pruning with cleaning out, avoiding disturbing soil in cold weather and ensuring good drainage as actions to control mites in tea plantations. However, this does partly contradict findings by Pande and Nandi (1983) who reported that C. carinatus actually prefers shaded tea, except in August, in Tripura, India.
Care should be taken when moving infested plants within economically important tea plantations, and between countries in the import/export plant trade. By introducing border control checks, such as those in place in Kenya (IPPC Secretariat, 2005), and by considering that mites can be carried on the clothing of personnel working amongst infested plants, measures to mitigate movement of the pest can be set in place.
Sharma and Kashyap (2002) reported that Syrphus sp., Coccinella septempunctata, Oxyopes sp. and the parasitoid Diaeretiella sp. are the most important natural enemies in tea orchards in general in Himachal Pradesh, India, where C. carinatus is one of the most important pests attacking tea bushes. The authors investigated the effect of pesticides on pests and natural enemies and found that deltamethrin, cypermethrin and ethion were highly toxic to Syrphis sp. and C. septempunctata. Conversely, applications of 1500 ppm azadirachtin or a combination of neem, triterpenoids and azadirachtin, or Bacillus thuringiensis were found to be safe to natural enemies.
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources: