Threshold-based spraying decision programs for the tomato leafminer, Tuta absoluta on tomato greenhouse

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Volume spécial - CSIEA2017, Article17

[Volume spécial - CSIEA2017, Article17]

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Abstract - The tomato leafminer miner, Tuta absoluta (Meyrick) (Lepidoptera, Gelechiidae) is an important insect pest of greenhouse tomatoes, Lycopersicon esculentum in Tunisia. The damages are severe and caused huge economic losses. Because no threshold levels are available for T. absoluta, many growers are applying chemicals at a calendar-based interval in which up to 20 sprays are provided. In order to diminish pesticide applications and to preclude damages to leaves and fruits, the implementation of a threshold level for optimum timing of chemical applications is required. A study was conducted in Saheline region of Tunisia to compare 8 alternative strategies for the control of the tomato leafminer, Tuta absoluta under greenhouse during two tomato cropping seasons in 2010 and 2011. The intervention protocols (strategies) included (1) ST1 = density of 1-4 galleries or larvae per plant , (2) ST2 = density of 5-8 galleries or larvae per plant, (3) ST3 = 9-16 galleries or larvae per plant (4) ST4= superior to 16 galleries or larvae per plant, (5) ST5 =systematically sprayed with chemicals, (6) ST6= systematically sprayed with organic product (spinosad), (7) ST7 unsprayed (control) and (8) ST8 = Sprayed alternatively with conventional chemical and plant extracts. The alternatives were evaluated with (1) the density of T. absoluta biological stages (eggs-pupae) in tomato leaves, (2) the percentage of larval mortality and (3) the fruit quality (the percentage of infested fruits). Results demonstrate the good performance of spinosad (ST6) in the reduction of fruit infestation. There is a difference between ST1, ST2, ST4 and ST5 regarding the larval density suggesting shifting from systematically chemical spray to spraying when population densities reach more than 16 galleries or larvae per plant (ST4). The strategy 8 (combination chemical – organic sprays) seems to be better than Strategy 5 (chemical control only) suggesting the need to integrate plant extracts as soft insecticides in the integrated pest management of the tomato leafminer.

Keywords: Tuta absoluta, tomato greenhouse, threshold level, insecticide sprays, plant extract, Tunisia.