IOBC delegates learn that pest management strategies for greenhouse vegetables remain quite challenging for growers
In an earlier issue of this magazine (September 2008), we authored an article that outlined many of the topics addressed at a meeting hosted by the International Organization of Biological Control (IOBC) held in the Netherlands this past April. In this issue, we would like to elaborate on a particular topic of discussion held at that meeting, the subject of organic production in greenhouse vegetables. Information on pest management in organic greenhouse vegetables, principally tomatoes and sweet peppers, was provided by representatives from Sweden, the U.K., and The Netherlands.
PEST MANAGEMENT IN GREENHOUSE ORGANIC TOMATOES
|Larvae or predatory stage of Aphidoletes aphidimyza feeding on aphids.|
Pest management in large-scale production of organic tomatoes is challenging and this is reflected in the experience of one of its major producers who has estimated that losses due to pest damage initially exceeded £100,000/ha/yr. In addition, the expenditure on IPM products was double that spent on conventionally grown tomatoes. As a result, efforts in pest management in organic tomatoes have focused on reducing costs and maintaining effectiveness to levels that are more on par with those of conventional production.
SOME EUROPEAN PREDATORS NOT AVAILABLE IN CANADA
Major pests in organic tomatoes included Macrolophus caliginosus, mealy bugs (Pseudococcus viburni), woodlice, spider mites and leaf miners. Macrolophus caliginosus is a predator (available in Europe but not in North America) that does a great job of suppressing several pests. But if their populations should exceed those of the pests, they will feed on the fruit trusses and cause premature fruit drop. Studies by researchers during 2006 and 2007 in commercial operations demonstrated that by restricting the numbers of this predator, they could benefit from the predation activity of this predator and still avoid damage to the fruits. They achieved this by strategically applying natural pyrethrins to reduce populations of the predator whenever deemed necessary.
DETAILED MONITORING FOR MEALY BUGS BEST DEFENCE
|Foxglove aphid showing characteristic dark spots at base of cornicles or “tail pipes.”|
Feeding by woodlice resulted in damage to leaves and stems, which in turn provided entry points for disease organisms. Although the presence of some predatory spiders may have contributed to suppression of this pest, the suppression level by the spiders was considered inadequate because of their long life cycle, slow population growth, and low predation rate. The most effective control has been ferric sulphate slug pellets.
Measures against spider mites and leafminers included precise monitoring methods for accurate releases of Phytoseiulus persimilis and Diglyphus isaea, respectively, transferring these biocontrol agents from areas of plenty to areas in need, and timely application of the starch-based material, Eradicoat T (not available in Canada) to the tops of plants to reduce feeding damage and egg laying.
PEST MANAGEMENT IN ORGANIC PEPPERS
Details of the area dedicated to organic peppers was not provided, but as an indication of activity in this type of production system, overall organic production in Sweden was estimated at 10 ha in 2006. In The Netherlands, the area of organic greenhouse vegetable production increased from 48 ha in 2004 to 82 ha in 2008. However, this increase resulted mainly from expansion of existing organic operations rather than conversion by new producers.
The major pest in both Sweden and The Netherlands is aphids, with the green peach aphid (Myzus persicae) and the foxglove aphid (Aulacorthum solani) being the most common species. In Sweden, banker plants with Aphidius colemani and A. ervi are the principal control agents, but problems have been encountered when other aphid species, e.g. Aphis nasturtii, occur despite releases of large numbers of natural enemies. Also, there was suspicion that releases of Amblyseius swirskii could have interfered with biocontrol of aphids because of predation by A. swirskii on eggs of the gall midge, Aphidoletes aphidimyza. It was also speculated that A. aphidimyza interfered with population build-up of the parasitic wasps, A. colemani and A. ervi.
MAJOR APHID CONTROL STUDY IN THE NETHERLANDS
In The Netherlands, pest management studies were done with 10 organic growers over a five-year period. For management of aphids, 10 species of biocontrol agents, banker plants, and two acceptable chemical products were used. One major conclusion of this study was that of all the biocontrol agents released, A. aphidimyza was the key factor in reducing aphid populations. Generally, though, they did not consider the control of aphids achieved to be satisfactory given that fruits still needed to be cleaned of sooty mold deposits, and growers suffered yield losses particularly due to damage by the foxglove aphid which stunted growth and stopped fruit production.
The researchers also concluded that further work was needed on several key areas such as improving the use of banker plant systems, compatibility of natural enemies, impact of climatic conditions, plants for nectar supply, and effects of environmental factors on performance of gall midge adults.
Financial support provided to Gillian Ferguson and Graeme Murphy to attend the IOBC, Greenhouse IPM Working Group Meeting in The Netherlands by Ontario Ministry of Agriculture, Food & Rural Affairs, the Canadian Greenhouse Conference (Gillian Ferguson) and the Cecil Delworth Foundation (Graeme Murphy) is gratefully acknowledged. Also, thanks to the Ontario Greenhouse Vegetable Growers for supporting this educational trip (Gillian Ferguson).
Graeme Murphy is the greenhouse floriculture IPM specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs at Vineland.
Gillian Ferguson is the greenhouse vegetable IPM specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs in Harrow.