Use of nets against viruses and their insect vectors in plastic greenhouses
Studies have been carried out in Italy and Spain on the use of nets in order to protect vegetable crops against viruses and their insect vectors.
1) Bemisia tabaci and tomato yellow leaf curl geminivirus (both EPPO A2 quarantine pests)
Several trials have been carried out in Sicilia (near Ragusa) in commercial plastic glasshouses of tomatoes with different types of nets placed on the apertures of the houses (in spring 1990, autumn-winter 1990-91, autumn 1991) and without insecticidal treatments. Tomato crops were regularly inspected for the presence of whiteflies (Bemisia tabaci and Trialeurodes vaporariorum) and of tomato yellow leaf curl. The efficacy of the different nets has also been tested in the laboratory with adults of B. tabaci. In the field, a good protection of the crop against whiteflies and excellent results for tomato yellow leaf curl were obtained with "antivirus" nets (10 x 20, 15 x 15, 12 x 12 mesh/cm¨). In the laboratory, these nets prevented adults of B. tabaci from escaping. However, the following types of nets: 'ombra 50' (6 x 8) and 'ombra 70' (8 x 10) gave inadequate protection as their mesh size is too large. The author concluded that the use of "antivirus" nets could provide a satisfactory protection of tomato crops in Sicily against tomato yellow leaf curl and its vector without chemical treatments.
2) Frankliniella occidentalis and tomato spotted wilt tospovirus (A2 and potential A2 quarantine pests)
Studies have been carried out in Spain near Murcia on the effects of a dense net (28 x 28 mesh/cm) on the incidence of Frankliniella occidentalis and tomato spotted wilt tospovirus. The nets were placed on the apertures of plastic houses of pepper (Capsicum annuum) cv. "Sonar" grown from December 1991 to august 1992. The crop was regularly inspected to study the evolution of population dynamics and occurrence of TSWV symptoms. The experiment included three treatments: 1) net and chemical applications against thrips, 2) net without chemical applications, 3) no net and no treatment. The results obtained showed that the net could delay the appearance of thrips within the crop (delay of 3 weeks) but then favoured its multiplication (probably by preventing the insect from escaping from the glasshouse). Two weeks before the end of the crop, percentages of virus infection were respectively for each treatment: 36 %, 63 % and 94 %. In addition, it was found that the total plant height and yield were improved by the use of nets. The authors concluded that under their experimental conditions, the use of dense nets in addition to insecticide treatments, could be a useful method against F. occidentalis and tomato spotted wilt tospovirus.
Sources
Nucifora, S. (1994) Mallas antivirus para la defensa del cultivo de tomate protegido contra Bemisia tabaci, vector del TYLCV.
Phytoma España, n° 57, 40-48.
Lacasa, A.; Contreras, J.; Torres, J.; González,A.; Martínez, M.C., García, F. Hernández, A. (1994) Utilización de mallas en el control de Frankliniella occidentalis (Pergande) y el virus del bronceado del tomate (TSWV) en el pimiento en invernadero.
Plagas, 20 (3), 561-580.