Research Centre Flakkebjerg, Danish Institute of Agr. Sciences, Slagelse DK-4200, Denmark

Background and objectives
Grey mould, caused by Botrytis cinerea, and infestations with whiteflies are two constant threats to tomato (Lycopersicon esculentum) production in heated greenhouses, particularly in long-season crops. Conventional practice for their management involves the application of synthetic chemical pesticides, however those which are currently registered for use in Denmark will no longer be available to growers by the year 2000. Management with biological control has been recommended for each problem [1, 2]. The in planta compatibility for the biologicals has not previously been studied. The objectives of this study were to find out if an interaction exists between the biologicals and what the nature of that interaction might be.

Materials and methods
Formulated preparations of T. harzianum isolate T-39 (Trichodex, Makhteshim Chemical, Israel) and V. lecanii (Mycotal, GC Garta, Demnark), applied by airbrush at manufacturers' recommended rates, were used in the following experiments. For studies on their effects on grey mould alone, the two biologicals were sprayed, alone and together, onto tomato (cv. Aromata) stem pieces that had been droplet inoculated with 1000 spore of B. cinerea applied to de-leafing wounds. Stems pieces were incubated for 1 week and evaluated for incidence and severity of grey mould. Similar treatments were applied to leaf disks that were infested with whitefly instars and evaluated for mortality and infection of the white flies 10 days after treatment with the biologicals. For the situation where both problems were present, plants were mechanically dwarfed and the biologicals were applied twice, the first time the day after de-leafing and inoculation with Botrytis, the second time 1 week later. Plants were evaluated 2 weeks after first application of the treatments. Data were evaluated by ANOVA.

Results and conclusions
Both T. harzianum and V. lecanii were significantly effective in affecting disease severity and also for control of whitefly populations under the high disease pressure and high infestation rate conditions of the experiments. The combination treatments where stem pieces, leaf disks or whole plants were co-inoculated with both organisms showed highly significant interactions between the agents. Their effects were non-additive. Whether this is the result of interference between the Trichoderma and the Verticillium or because both organisms are missing the same group of infections remains to be investigated.

1. Elad Y, Malathrakis N, Dik A, 1996. Crop Protection 15, 229-240.
2. Hall RA, 1982. Annals of Applied Biology 101, 1-11.