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T. simplex causes direct damage by emptying plant cells. Sucking activity of the larval and adult stages causes injury on foliage, flower spikes and corms (Denmark and Poe, 1972) . The damage on the foliage first appears as silvery-white scars. Injured foliage and deformed flowers soon turn brown and ruin the marketability of the flower spikes. Severely infested buds come out poorly and flowers are malformed (Mantel and Van de Vrie, 1988). The corms are fed upon in storage and become dry and rough with red-brown patches.
Heavy rain or sprayed water will dislodge many thrips of all mobile stages from the plant. Aluminium foil mulch decreased the damage to saleable flowers of Gladiolus in field experiments with thrips-free corms in Maryland, USA (Smith et al., 1972). Aluminium foil was significantly better than black plastic. In storage rooms, T. simplex was effectively controlled by storage of infested corms at 2°C for 6 weeks or at 5°C for 8 weeks (Conijn and Groen, 1989). At 9°C the thrips infested healthy corms very slowly and some of the thrips survived even after 20 weeks. Water dips (46°C) were not phytotoxic to treated corms of the variety 'White Friendship' (Schuster et al., 1984).
Inundative releases of Amblyseius barkeri achieved successful control of T. simplex on Gladiolus corms in the Netherlands (Conijn and Groen, 1990; Conijn, 1993).
Experiments in Australia on the susceptibility of six Gladiolus cultivars resulted in percentages of marketable spikes ranging from 1.3 to 50.5% (Hargreaves and Cooper, 1980a).
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:
T. simplex has been reported to be an important pest in many countries, but the amount of yield loss is seldom given. In Indonesia this thrips species is the main pest of the Gladiolus cut-flower cultivation (Mutia Erti Dwiastuti and Yuniarti, 1998). After the appearance of T. simplex in the USA, it spread rapidly (Herr, 1934). Serious damage was reported in Ontario, Canada, in 1929. Considerable injury occurred in Ohio, USA, as early as 1930, and during the past 3 years most of the Gladiolus plantings all over the USA were damaged by this pest. In Ohio, the loss per acre on Gladiolus cut flowers alone, as a result of the damage caused by T. simplex, may amount to over $3000 (Herr, 1934). In addition to the loss from cut flowers, the damage to the foliage caused by the thrips results in stunted growth and hence fewer high quality corms. The latter is not a serious problem in Florida, USA, but damaged foliage and deformed flowers ruin the marketability of the flower spikes (Denmark and Poe, 1972).