Combined use of insect pathogenic fungi and nematodes against the onion thrips, Thrips tabaci, in the field

In the year 2003, field trials against Thrips tabaci, an important pest insect in onion, leek and chives, were conducted at four different sites with commercially available products based on insect pathogenic fungi and nematodes. The trials were performed according to the EPPO guideline PP 1/85(3) for the efficacy evaluation of insecticides “Thrips on Outdoor Crops”. As a chemical standard Perfekthion® was used in onion. In leek, Spruzit® and Neudosan® were applied alternately. The biocontrol products used were Mycotal® (Lecanicillium muscarium, former Verticillium lecanii, Koppert NL), PreFeRal® (Paecilomyces fumosoroseus, Biobest BE), Naturalis L® (Beauveria bassiana, Intrachem IT), Nemaplus® (Steinernema feltiae, E-Nema DE) and Nemagreen® (Heterorhabditis bacteriophora, E-Nema DE). They were applied either alone or in a mixture using common spray equipment. A wetting agent was added. The nematodes were applied at a rate of 1x106 infective juveniles/m². The dosage of the fungi was 1 kg (1.5 l in the case of Naturalis L®)/ha. The treatments started mid June and were repeated up to six times in weekly intervals. Throughout the summer, T. tabaci was recorded only in medium numbers (mean of 30 specimen/plant max.) at all four sites. In two trials (onion, Mainz; chives, Horkheim), no differences between treatments and the untreated control could be detected. In the third trial (onion, Schifferstadt), a significant reduction was recorded for the treatment ‘PreFeRal+Nemaplus’, both in the number of thrips/plant (2 compared to 6 in the control, respectively) and the frequency of infestation (38% compared to 93% in the control, respectively), one week after the final application (three times in total). Also in the fourth trial (leek, Bonn), the number of thrips/plant was lowest for the treatments ‘fungus+nematode’ (4 compared to 7 in the control, respectively; fungus here: Mycotal®) one week after the final application (six times in total). In this trial, yield was measured additionally, and it turned out, that the weight/plant registered for the treatments ‘Nemaplus’ and ‘Mycotal+Nemaplus’ was 20% higher than in the control (425 and 412 g/plant compared to 345 g respectively). These trials show that the use of insect pathogenic fungi and nematodes in the field is possible, confirming results of others collected in Great Britain and The Netherlands. In view of the extreme weather conditions in summer 2003 in Germany, and in comparison to the effect of the chemical standards, the results gained with the biocontrol agents are regarded as very promising. However, more experiments are necessary.