Further developing integrated pest management for lettuce (VG05044)

This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

Lettuce integrated pest management (IPM) had been in development in Australia since 1998 with lettuce growers able to manage the then key pest, Helicoverpa spp. with a range of integrated control options. The spread of western flower thrips (WFT), a effective vector of tomato spotted wilt virus in lettuce during the previous decade and the arrival of the currant lettuce aphid (CLA) into Tasmania in 2004 and its subsequent movement into all major lettuce producing areas provided an effective barrier to the widespread adoption of an IPM strategy that utilized pest natural enemies or ‘beneficials’.

A Hort Innovation (which was then Horticulture Australia Limited) project in 2004-5 demonstrated that CLA could be controlled in Tasmanian lettuce crops by farmland predatory insects. The beneficial insects were harnessed by the grower using IPM concepts such as sequential, adjacent plantings, looking before spraying and choosing selective or ‘soft’ pesticides as far as possible. The predators entered lettuce hearts, ate the aphids and moved on before harvest. Insecticidal sprays failed because this pest lived deep inside lettuces unlike other aphids on lettuce.

CLA was one of the few insects where there were lettuce varieties that were resistant to attack (Nas-resistant). These varieties had been selected and bred in Europe where CLA originated and was a major lettuce pest. Some of the varieties available to Australian growers particularly the ‘fancy’ lettuce were Nas-resistant and the lettuce seed companies were all trying to incorporate Nas-resistance into all their lettuce varieties. In the northern European summer of 2007 a new CLA biotype was found feeding in Nas-resistant varieties which emphasises the importance of not relying on a single control mechanism. In 2006 68 per cent of growers were using some Nas –resistant varieties.

Most (94 per cent) Australian lettuce growers chose to use a systemic (travels from roots through plant) insecticide on Nas-susceptible lettuce. This insecticide while very effective for controlling aphids for 6-8 weeks did not control caterpillars nor WFT and research had shown that it could cause secondary poisoning to an important aphid and caterpillar predator, the brown lacewing.

This national vegetable levy funded project aimed to extend the results of the 2004-5 northern Tasmanian trial into southern Tasmania and the Sydney basin and to monitor the transition that Victorian IPM growers were making with the arrival of CLA. A range of other monitoring and research activities were included to assist with addressing regionally specific barriers to IPM adoption.

In 2005-6, iceberg and loose-leaf lettuces were grown under commercial conditions by two major growers near Hobart. Control in iceberg lettuce was good for six plantings and management of thrips was integrated with that of aphids. In loose-leaf lettuce control was initially promising but failed after the sixth planting.

Since CLA arrived in Victoria in May 2005 it had been controlled using an IPM strategy on several commercial farms in both Werribee South and Cranbourne. CLA populations on susceptible lettuce without insecticide drenches were effectively controlled by aphid predators, particularly the brown lacewing.

A winter IPM trial in the Sydney basin failed to control CLA in susceptible undrenched lettuce. Aphid predators were in very small numbers over the winter but increased in the spring and effectively controlled CLA in susceptible lettuce.

CLA was not being found on weeds in and around lettuce production areas. In most areas the CLA population dynamic through the year was difficult to study with most lettuce being either CLA resistant varieties or treated with a systemic insecticide that generally lasted the whole crop.

A survey of soil predatory mites found a Pergmasus species present in lettuce soils in surveys in South Australia, Victoria, Tasmania and NSW. Applying composted greenwaste to the soil greatly increased the numbers of predatory mites. It was not yet known whether increasing numbers would contribute significantly to controlling CLA or thrips.

61 per cent of lettuce growers surveyed identified as IPM growers, 100 per cent of IPM growers and 83 per cent non-IPM grower monitored their crops for pests but less than 40 per cent looked for beneficials. 28 per cent used a consultant to monitor. 42 per cent of non-IPM growers were ‘calendar’ sprayers – spraying on a regular – usually weekly basis.

Consultants who monitored lettuce were confident in their pest identification, less so of their disease identification. They were confident when to spray and to assess it’s effectiveness but not particularly confident about providing advice on beneficials or their conservation. Consultants who were confident about their knowledge and skills with using beneficials were positive about growers attitudes to IPM whereas consultants lacking confidence with beneficials felt growers negative attitudes to IPM was the major barrier.