Industry representative: Dr Philip Morley
AHDB Horticulture Cost: £17,380
Summary: Tuta absoluta arrived in the UK in 2009 and rapidly became the most important pest of home-grown tomatoes. By 2013, HDC projects PC 302 and PE 020, and associated studies, had developed a completely new IPM strategy for use against the pest and this was detailed in HDC Factsheet 02/14. The programme was based on the predator, Macrolophus pygmaeus, integrated with some physical control measures and the chemical insecticides, spinosad (Conserve), chlorantraniliprole (Coragen) and indoxacarb (Steward). Macrolophus pygmaeus was released at the start of the growing season so that it would start to provide some control of the pest by late spring or early summer. When the pest arrived, it was allowed to colonise the crop but population growth was slowed by applying spinosad through the irrigation system before the first generation of caterpillars completed their development. If necessary, a high volume spray of chlorantraniliprole was applied as a second line of defence during the summer to keep the pest and predator populations in balance. If crop monitoring indicated that a clean-up spray was required at the end of the season, then the third insecticide, indoxacarb, was used to reduce the number of T. absoluta surviving in the glasshouse to infest the next crop. The three insecticides used in the IPM programme were from different Insecticide Resistance Action Committee (IRAC) Mode of Action Classification Groups and, together with the biological control agent, should have formed a robust resistance management strategy. Nonetheless, a strict warning about maintaining an effective insecticide resistance management strategy was incorporated in HDC Factsheet 02/14.
The IPM programme was very successful and British tomato growers admit that they became complacent about the pest. However, during the 2015 and 2016 growing seasons several growers began to experience difficulties with various components of the programme.
Resistance to Conserve has now been confirmed at three nurseries (via PE 028 and independent testing). Coragen treatment failures at two sites in 2016 are still under investigation but also seem to be due to resistance. If so, this would be consistent with the development of resistant populations of T. absoluta in Italy and Greece (Rodiakis et al., 2015). Steward has rarely been used against T. absoluta in the UK because the pest population has usually been reduced to an acceptable level by M. pygmaeus before the end of the growing season. However, one British grower has experienced treatment failures with this product (Holt & Jacobson, Pers. Com. 2011).
Although the primary biocontrol, M. pygmaeus, had for several years given very good control of T. absoluta from May-June onwards, results in 2016 were inconsistent. Some populations crashed during the summer for inexplicable reasons. This has led to questions about variation between different strains of M. pygmaeus and the possibility that some strains have been harmed by Conserve and / or some of the fungicides that have recently become available. The latter have not yet been tested for compatibility with M. pygmaeus and this information is urgently required.
These control failures have made it clear that the British tomato industry must take measures to remain one step ahead of this potentially devastating pest. The TGA TC has worked closely with CRD, CBC (Europe) and Fargro Ltd to facilitate the rapid authorisation of Isonet-T (a pheromone-based mating disruption system). This product has the potential to slow down T. absoluta population growth in the early part of the season while M. pygmaeus are becoming established; thereby providing an alternative to Conserve via the irrigation in the IPM programme. Unpublished reports from mainland Europe are very promising but a conflicting study has indicated that T. absoluta exhibit parthenogenesis (production of eggs without mating) which would clearly compromise the efficacy of this system (Megido et al,, 2012). Crop-scale trials are urgently required to determine the true potential of this product.
AHDB project, PE 028, identified two insecticides (azadirachtin and emamectin benzoate) from hitherto unused IRAC Classification Groups which could replace the insecticides already compromised by resistance. The compatibility of azadirachtin (NeemAzal) with M. pygmaeus is unclear – it may be harmful when applied as a HV spray but compatible when used via the irrigation system. Preliminary efficacy and compatibility tests are therefore required to determine whether it should be investigated in greater depth. It has been agreed with AHDB that efficacy work will be done via the new Sceptre+ project.
Aim: To maintain the viability of tomato production in the UK by avoiding losses caused by Tuta absoluta and reducing chemical pesticide use by filling important knowledge gaps in the IPM programme against that pest.
1. To determine the compatibility of three strains of Macrolophus with specific HV sprays
2. To determine compatibility of three strains of Macrolophus with systemic application of Conserve.
3. To investigate the efficacy of the Mating Disruption system on a commercial crop scale
4. To transfer knowledge to the UK tomato industry
Benefits to Industry:
Tuta absoluta is currently the most important pest of tomato crops in the UK. For example, at one nursery in 2012, 30% of fruit were damaged by the pest and graded out during June and July causing losses of approximately £50k per hectare to that grower for that period alone. The Macrolophus-based IPM programme prevented such damage for over three years but several components of the programme have now broken down. The industry urgently need to improve the performance of the predator and find alternative IPM compatible control measures. From the example cited above, payback from this project could be achieved from less than one hectare of tomatoes in just one growing season.