Vol. 1, Issue4 (April 2001)

This page brought to you with the co-operation of the Alberta Research Council and Alberta Agriculture, Food & Rural Development.


This week, thrips populations recovered from a low of 2 to 12 thrips per trap, the highest we have recorded so far this season. Thrips have been detected on marigolds and petunias. In one case necrotic, circular spots were found on leaves that appeared to be due to TSWV. Your monitoring for thrips should now include visual inspection as well. Blow softly on flowers and growing points to make the thrips active. Black feces and silvery, flecked areas on leaves are signs of thrips presence. · If you are planning to use a biological control agent such as the predatory mite Amblyseius cucumeris, Amblyseius degenerens or predatory bug Orius insidiosus begin as soon as thrips are caught on sticky traps.

Fungus Gnats

Fungus gnat populations remained at the same levels as last week, 8 per trap. Citation is a registered insecticide for fungus gnat control. In addition to the yellow sticky traps, potato disks can be used to monitor fungus gnat larvae. Insert 2-3 cm (1-inch) cubes or disks of peeled raw potato about half inch deep into media. Inspect the underside of each potato and the soil immediately beneath it weekly. The numbers of larvae you find will be an indication of the success or otherwise of your control efforts. One grower used larger yellow sticky traps to physically reduce the populations of fungus gnats but you have to use a large number of them throughout the greenhouse. Reducing the algae in greenhouses should be a priority.


There were no whiteflies caught in traps this week. This does not mean that your greenhouse does not have any whiteflies. In addition to traps check for the plants, which are closer to exhaust fans and/or located away from the the main traffic areas. Such plants escape examination and that is where whiteflies like to "hide".

Shore fly

Shore fly numbers generally continued to decline in places where Citation® was used. Their numbers declined dramatically, by about 97%. Citation is applied either as a spray or drench to all surfaces where insect pests may breed. Citation will not control the adult stage of shore fly.

Spider mites

We have found infestation of spider mites in dracaenas. Remember yellow sticky traps are not effective for monitoring spider mites. You must inspect foliage closely using a hand lens of 10X magnification. Continue monitoring. Do not wait for a web to be formed then it is too late to control them.


Aphids have been observed on peppers and tomatoes. Don't let them get out of hand. Good coverage of insecticides is needed to destroy them. Aphids multiply very rapidly because they are born pregnant. An adult aphid can give birth to as many as 76 offspring.

We would like to expand the number of greenhouses we monitor. We would therefore like to invite growers that monitor their greenhouses to send to us their yellow sticky traps. Traps containing insects can be wrapped with clear plastic and sent through the post to us. We will identify and count your insects for our study. In return you will receive a copy of the your trap information e.g. insects identified and the numbers done by experts. Call us for further information if you want to participate in the network.

Yellow sticky traps on their own will not control pests in the greenhouse. It is just an aid for monitoring your pests.