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Integrated control of pests of ornamentals | AG0189 |
David Williams, Knoxfield
June, 2000 |  |
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Pest outbreaks often result from the combination of several ecological factors. The potential for pest problems increases as the area planted to a single crop increases. The use of nitrogenous fertilisers may favour the pest feeding on the plant. Some pesticides may make crop plants more susceptible to attack by other pests by altering the physiology of the plants.
Depending on the crop and pest complex, it may be possible to devise cultural methods that make environmental conditions unfavourable for rapid development of some pests. The use of selective pesticides and/or better timing of pesticide applications allows control of some pests without harming predators and parasites of others.
Integrated control or Integrated Pest Management (IPM) is a system in which chemical, biological and cultural methods of control are integrated in such a way that pest populations are prevented from causing economic damage.
What are the advantages and disadvantages of IPM
Better timing, selection and application of pesticides reduces the amount of chemical residues on crop plants and gives greater safety to workers handling the plants. The use of biological control agents and less pesticide reduces the chances of pests developing resistance to pesticides. It also reduces the unpopular and often expensive problem of having to apply pesticides outside normal working hours.
There are, however, problems associated with the use of integrated control. Growers and pest managers need to have a good understanding of pest biology monitoring techniques and threshold sizes of pest populations. They must become more aware of the implications of each course of action they take.
Some biological and cultural control methods do not readily lend themselves to the economic production of some crops. The availability of suitable pesticides may be restricted because no registration exists or information on phytotoxicity, residues, etc., is not available. Sometimes the use of more selective chemicals leads to an increase in secondary pest problems because such pests are no longer controlled by the broad-spectrum chemicals previously used.
What is needed for IPM to work
Growers must be committed to the principles of IPM. They must be prepared to accept some damage provided it is not causing economic loss. Growers must be prepared to either spend time monitoring populations of pests in their crops or to employ someone to do the monitoring for them. Growers and pest managers must be supplied with adequate specific information on the requirements of biological control agents, monitoring methods, suitable pesticides and guidelines on how and when to spray. Any biological control agents used must be available for delivery at any time and in sufficient numbers to rapidly build up and exert control.
Examples of IPM in the ornamentals industry
In Europe the parasitic wasp Encarsia formosa is used to control greenhouse whitefly. and the predatory mite Phytoseiulus persimilis used to control twospotted mites in glasshouses. The biological control agents are released annually and intensive guidance is given to the grower on a commercial basis by the suppliers.
Adults of E. formosa require sunlight and a sugar supply to stimulate flight in search of hosts. They are very efficient at finding and parasitising even single individuals of whitefly larvae over many metres in dense foliage. Parasitised whitefly larvae turn black and it is easy to follow progression of the bio-control.
P. persimilis behaves differently. It wanders actively over the leaves until it finds its prey, usually in localised patches, which it then settles down to consume. It eats eggs, immatures and adults. Once it has eaten out the local population of twospotted mites it moves on in search of more prey. P. persimilis can also be dispersed in the wind from cooling fans and on the clothing of workers as they move about the glasshouse.
In Australia the ACT Parks and Conservation Services uses integrated pest management in its glasshouses (see Australian Horticulture Jan. 1986. Nazer & Clark "Pest management in glasshouses"). They use P. persimilis against twospotted mites and Bacillus thuringiensis against caterpillars. Both of these are available commercially. Other biological control agents used whenever possible, are the parasitic wasps Aphidus colemani (against aphids) and Encarsia formosa (against whitefly) and the mealybug ladybird Cryptolaemus montrouzieri against mealybugs. Advice on the availability of biological control agents can be obtained from Australasian Biological Control, which is an association of beneficial arthropod producers. Yellow sticky traps are also used to mass trap whitefly.
Research conducted in NSW indicated that where P. persimilis is being used to control mites in glasshouses, problems may occur if plants are isolated from each other, or are grown in hanging baskets, because twospotted mites may build up to damaging numbers before the predators find them. Temperatures above 38°C may kill the predators and cause an outbreak of mites, but whitewashing glasshouses to reduce heat buildup will minimise the risk. Suppliers of predatory mites should also be asked to provide a list of chemicals known to be toxic to the strain of predators being supplied.
The use of insect pathogens is also under investigation. A pathogen can be introduced into a pest population in a small amount and, if conditions are right, the infection will spread throughout the population restraining it below economic size.
Pathogens usually spread effectively only at high pest densities. To overcome this a pathogen can be applied as a microbial insecticide. In this method copious amounts of pathogen are applied to cause disease in all or most of the pest population. Various pathogens have been considered for use in integrated control.
Research by the CSIRO and the Tasmanian Department of Agriculture has demonstrated the potential for using a nematode Heterorhabditis heliothidis to control blackvine weevil infesting potted ornamentals. Affected plants have to be drenched with a suspension of the nematodes, which seek out, infest and destroy the weevil larvae.
The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.
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