|
Two-spotted mite on ornamental plants | AG0184 |
David Williams, Knoxfield
June, 2000 |  |
To view the Adobe Acrobat file, you will need the Adobe Acrobat reader. |  PDF 41 kb | |
Description
The egg of the twospotted mite, Tetranychus urticae, is minute, globular and an almost transparent pale yellowish-white. The larva that hatches from the egg has six legs, is pale yellowish-white, minute and oval. The larva moults to become an eight-legged nymph, which becomes the mature mite after two further moults.
The adult female is about 0.5 mm long, the adult male about 0.3 mm long. In the summer feeding stage the adult females are a yellowish-green, with two pronounced dark spots, one on either side of the body. In males these spots are less conspicuous. Both sexes possess two reddish eye-spots. Only adult females overwinter, after changing to the orange-red, non-feeding stage.
Damage
Both nymphs and adults damage plant foliage by piercing the cells and sucking the contents, causing collapse and death of the cells. The mite is a profuse web-spinner in its active stages. Infested leaves become pallid and may become bronzed and shrivelled. The mites are particularly damaging in hot, dry weather when a life cycle may be completed in just over a week. Plants near dust sources such as dirt roads are particularly susceptible to mite attack.
Plants attacked
Twospotted mites attack a wide variety of plants including peaches, apples, cherries, pears, plums, berries, ornamentals and many vegetables.
Life cycle
The development of the overwintering or hibernating form is initiated by shortened daylength, decreased temperatures and unfavourable food supply. Overwintering females stop feeding and egg-laying, become orange-red and move to shelters on the ground and in cracks in the bark of lower regions of trees.
Overwintering is terminated by the increased temperatures in spring. The mites leave their overwintering sites and lose their red colour as they start to feed.
Mites living in protected environments, such as glasshouses, do not hibernate overwinter but continue to feed and reproduce. The females lay up to six eggs a day and usually lay a total of 70 or more. Hatching occurs 3-10 days later, depending on the temperature. Males develop from unfertilised eggs whereas females develop from fertilised eggs.
The young mites mature in 4-12 days, depending on temperature, and may live for another three weeks or more. In hot weather the complete life-cycle may be as short as two weeks, and all stages may be found at the one time.
Figure 1. The twospotted mite life-cycle
Control
There are two problems in controlling twospotted mite. The use of broad-spectrum insecticides greatly reduces the number and effectiveness of beneficial insects, and mite populations have developed varying degrees of resistance to several miticides.
If chemical control is required, careful selection of a miticide is important. There are several effective miticides available but they may be phytotoxic to some plants.
Twospotted mite has been successfully controlled in Victorian apple and peach orchards by the use of an integrated approach in which chemicals are used in conjunction with the introduced predatory mite Typhlodromus occidentalis. T. occidentalis is now available commercially in Australia. Overseas the predatory mite Phytoseiulus persimilis is used in glasshouses to control twospotted mite. P. persimilis is also available commercially in Australia. The predatory mites are susceptible to different pesticides and growers are advised to obtain a list of pesticides toxic to the predators. Such lists are available from the suppliers of the predators. Further information on availability of biocontrol agents can be obtained from the Association of Beneficial Arthropod Producers.
For effective pest and disease control, correct diagnosis is essential. A commercial diagnostic service is available at the Institute for Horticultural Development. For further information, contact the Diagnostic Service. ph: (03) 9210-9222 or fax (03) 9800 3521.
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.
|
