This report provides the results of research investigating the use of cultural control options that would encourage populations of key predatory insect and mite species that prey on pests of vegetable crops.
The target pests were primarily aphids and thrips. These are important groups for leafy vegetables as they include lettuce aphid (Nasonovia ribis-nigri) and western flower thrips (WFT) (Frankliniella occidentalis), both of which are resistant to a range of insecticides. WFT is also an important vector of tomato spotted wilt virus.
In particular the project looked at whether or not certain plantings of non-crop plants could assist with pest control in leafy-vegetables.
Rye-grass was selected because we knew planting it could fit in with existing farm practice and it grew well at the time of year that it was required.
The project also investigated the potential of other management practices such as addition of composted fowl manure and using flowering weeds to augment populations of predatory and parasitoids insects and mites.
Once again, these practices were selected because they could fit in with existing farm practices and so could be easily adopted if successful.
Such a project could only be carried out on farms where IPM is being practised, and results will only be of value to farmers using an IPM approach. [Integrated pest management involves using biological and cultural control measures, supported where necessary by pesticides].
Several farmers in Werribee South and Cranbourne, in Victoria, agreed to take part in the trial and plant non-crop strips. All of the trials were on a whole paddock basis, not small plot trials.
It is clear that there are several useful cultural control measures that are practical, that vegetable growers can use to encourage beneficial insects and mites.
That is, the cultural and biological components of an IPM strategy can be strengthened. This project has demonstrated that it is possible to use insectary plantings and made a part of normal vegetable production methods.
The use of composted organic material was also shown to increase populations of soil-dwelling predatory insects and mites. The beneficial insects and mites that are encouraged by these different methods fall into two categories, transient and resident.
The strip plantings of cereals attract transient brown lacewings (M. tasmaniae) as they are dispersing through vegetable production areas in spring. They will stop in these strips but not in a bare paddock, and so it is a means to increase the population of predators on a paddock going into vegetable production.
The organic composts can be used to increase the populations of resident soil dwelling predators. The cultural control component of IPM is often given less emphasis than the biological or chemical components but this project has shown that it provides the basis for control of 17 key pests.
There are many different types of cultural controls that are available to farmers that are beyond the scope of this project but many are site or crop-specific. This work has focussed on methods to increase populations of beneficial invertebrates.
Providing a suitable habitat for predatory species increases the role of both the resident and transient biological control agents. Planting insectary crops has also the added benefit of helping make growers aware of the broader approach to controlling pests by deliberately acting to encourage beneficial species.
It is therefore a good starting point for those just adopting IPM, to emphasise the importance of cultural controls within an IPM strategy. There is also potential for certain existing flowering weeds to be used to increase populations of beneficial insects by providing pollen and nectar.
The situation that exists in areas such as Werribee South is that on land adjacent to crops that is usually not owned or managed by the farmer, there are often flowering weeds of different species. Management of these is restricted to limited herbicide applications which can result in bare ground or poor control of established weeds.
Replanting these strips of land with native plants may be desirable (see Revegetation by Design Project) if particular species can be recommended, but no local species have been trialled in this area and it is currently not achievable by the grower, and is not a priority for them.
This especially relevant for farmers leasing land on a short-term basis. We suggest here that there is scope to utilize some existing flowering weeds in preference to attempting to achieve bare earth.
The main concern is whether or not certain species of weeds will also encourage pests or be a reservoir of disease. Therefore, in brassica production areas brassica weeds would not be suitable but aniseed weed could be ideal.
However, in celery production areas aniseed weed could harbour celery mosaic virus and so would not be suitable. The observations in this project have been that there are often large strips of flowering weeds on land adjacent to crops anyway, but that some of them could be considered useful rather than just weeds. WFT Control.
The studies on WFT in lettuce crops showed that this species was surviving a range of insecticides, including drenches of imidacloprid. It was present in both IPM grown and non-IPM crops but in all sites studied the numbers of WFT never increased in IPM crops.
WFT has been present in Victoria for many years but in Werribee South now has the potential to cause serious problems.
The small number of IPM lettuce sites available makes firm conclusions difficult, but the results are consistent with the hypothesis that a range of predators, both resident and transient, are present in IPM crops and are preying on WFT, giving control. In the non-IPM crops the number and range of predators is much less and WFT populations have increased. The naturally occurring predators are able to deal with WFT and we suggest that they have been doing so for many years.
So there is no requirement to attempt to commercially rear and release these predators outdoors but simply not to kill them where they occur. It is much easier to avoid problems with WFT than to have to deal with this pest when it is in high numbers.
Similarly, there is no need to develop specific strategies for WFT. It is dealt with through an effective IPM strategy covering all pests in leafy vegetables.
This study was funded by Horticulture Australia Limited and AusVeg.
We thank all of the farmers that collaborated in this project, especially Tom and Theo Schreurs (J & JM Schreurs and Sons); Darren Schreurs (Peter Schreurs and Sons); Paul Gazzola (Gazzola Farms); John Fabbian; Paul Samarges; Andrew and Joseph Fragapane (Fragapane Farms); Jim Pateras; and Stan and Fred Velisha (Velisha Bros.), Con and Adam Ballan.
We thank Dr. Jenny Beard (AQIS) for mite identification and Kate Lorey for conducting laboratory trials