Vol. 1, Issue 3 (April 2001)

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


This week, thrips populations dropped from a mean of 7 per trap to 2 thrips per trap. It seems the grower's personal economic threshold was around this figure and therefore took action to control the thrips. Several insecticides are recommended for thrips control. Avid and Admire are among the latest in the grower's insecticidal arsenal for controlling thrips, although both products are more effective when used against pests other than thrips. Always remember to follow the label recommendations. Symptoms of Tomato Spotted Wilt Tospovirus (TSWV) were seen on begonias and impatiens and the best way to control the virus is to make sure that thrips are controlled.

Fungus Gnats

Fungus gnat populations increased. Citation is a registered insecticide for fungus gnat control. Nemasys (Steinernema feltiae) is made up of infectious nematodes, which control a wide variety of pests such as fungus gnats, shore flies and root maggots. They are not harmful to humans, earthworms, beneficial insects or plants. Since nematodes move in the growing medium on a film of water, it is important that the media be moist. 50 million nematodes cover 2500 sq. ft. of greenhouse area.


There were no whiteflies caught in traps this week. This could be the result of insecticides used to control the thrips. Avid and Admire both give good control of whiteflies. Therefore, continue to monitor using a combination of foliage inspection and your yellow sticky traps. Frequent foliage inspection will reveal the presence of nymphs. Eggs are laid on the underside of leaves. At this stage you are more likely to find eggs and immature stages on younger leaves. Continue monitoring and remember huge numbers of whiteflies can build up in a very short time.

Shore fly

Shore fly numbers generally continued to increase. However, in places where Citation was used their numbers declined by about 63%. Citation is applied either as a spray or drench to all surfaces where insect pests may breed. This includes potting media surfaces, bench tops, and areas under benches. Citation will not control the adult stage of an insect pest.

Spider mites

Yellow sticky traps are not effective for monitoring spider mites. You must inspect foliage closely using a hand lens of 10X magnification. Look for small pinhead type of injury on the upper surface of leaves and young spider mites on the underside of the leaves. The biological control agent Phytoseiulus persimilis is effective in controlling spider mites in greenhouses. We have found heavy infestation of spider mites in dracaenas. Look for yellow-orange spots on the upper side of leaves and spider mites on the underside of the leaves. If a web has been formed then it is too late to control them. Discard the plants immediately by putting them in a plastic bag prior to carrying them through the greenhouse.