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Spider mite on orchids Tetranychus urticae They are really bad in Melbourne This year 2019

I felt the previous blog, interesting as it was , needed padding out a little, so here goes. 



Before we start ,I did a small experiment where i left a lightly infested Australian Dendrobium 50mm tube in my office in dry,low humidity dark conditions for 14 days. 

At the end the plants was nearly dead with mite infestation and was totally limp.

So in the right (or wrong for the orchid!) conditions ,these two spotted mites will sererly damage your orchids in under two weeks The photos below show the damage.

Note the white peppery patches.  Although a little blurry the  mites and webs are easily seen.


I have never had a lot of success with organic and biological controls. But I am certaily open to recieving results that we can post as a new blog. 

Spider mite development differs somewhat between species, but a typical life cycle is as follows.

The eggs are attached to fine silk webbing and hatch in approximately three days.

The life cycle is composed of the egg, the larva, two nymphal stages (protonymph and deutonymph) and the adult.

The length of time from egg to adult varies greatly depending on temperature. Mid twenties and higher is perfect and even higher temeratures cause mass hatchings.

Under optimum conditions (27.c), spider mites complete their development in five to twenty days.

There are many overlapping generations per year.

The adult female lives two to four weeks and is capable of laying several hundred eggs during her life.

 Overwintering females hibernate in ground litter or under the bark of trees or shrubs



All mites have needle-like piercing-sucking mouthparts. Spider mites feed by penetrating the plant tissue with their mouthparts and are found primarily on the underside of the leaf. All spider mites spin fine strands of webbing on the host plant — hence their name.

The mites feeding causes graying or yellowing of the leaves. Necrotic spots occur in the advanced stages of leaf damage. Mite damage to the open flower causes a browning and withering of the petals that resembles spray burn.

When twospotted spider mites remove the sap, the mesophyll tissue collapses and a small chlorotic spot forms at each feeding site. It is estimated that 18 to 22 cells are destroyed per minute. Continued feeding causes a stippled-bleached effect and later, the leaves turn yellow, gray or bronze. Complete defoliation may occur if the mites are not controlled.

Spider mites are the most common mites attacking woody plants and the twospotted spider mite is considered to be one of the most economically important spider mites. This mite has been reported infesting over 200 species of plants.

Fruit crops attacked include blackberries, blueberries and strawberries.

A number of vegetable crops such as tomatoes, squash, eggplant, cucumber are also subject to twospotted spider mite infestations and damage.


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