Vol. 1, Issue6 (April 2001)

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

In this issue we recap the general pest situation and the general management principles we have discussed earlier.

Thrips

Thrips are of major concern this season. Plant damage symptoms include distorted leaves and stunted new growth. Thrips transmit tospoviruses such as Tomato Spotted Wilt Tospovirus (TSWV) and impatiens necrotic leaf spot virus (INSV). In addition to yellow sticky cards, monitoring for thrips should include some visual inspection. Thrips prefer confined spaces. Black feces and silvery, flecked areas on leaves are signs of thrips presence. Generally, adults are found deep in flowers, larvae in growing points, and pupae in soil. Thrips are difficult to control with insecticides. To ensure that all stages of thrips' lifecycle are targeted, apply any particular insecticide three times at 5-day intervals. Effective insecticides include Trumpet® (bendiocarb), Malathion, and Nicotine Sulphate.

Fungus Gnats

Fungus gnat populations are high. Most of the insects' life is spent as larvae and pupae in organic matter or soil. In addition to the yellow sticky traps, potato disks can be used to monitor fungus gnat larvae. Good sanitation is important for fungus gnat control. Reducing the algae in greenhouses should be a priority. Commercially available insecticides include Dimilin®, and Citation®

Whitefly

Whiteflies have been reported from some greenhouses. Continue to monitor using a combination of foliage inspection and yellow sticky traps. Frequent foliage inspection will reveal the presence of nymphs. Eggs are laid on the underside of leaves. Impower® (imidcaloprid) and Enstar II® are registered for control of whiteflies.

Shore fly

The shore fly population is increasing steadily. They prefer damp areas and algae. Dimilin® is also registered for shorefly control. 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

Inspect foliage for spider mites using a hand lens of 10X magnification. 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. Yellow sticky traps are not for monitoring spider mites. Commercially registered miticides for spider mite control include Vendex®, Kelthane, Dynomite®, and Avid®.

Aphids

Aphids have been observed on peppers, tomatoes, and periwinkle. Aphids multiply very rapidly because they are born pregnant, do not need to mate and give birth to live young (no egg stage). They are usually seen on stems. Also look for white shed skins or honeydew on the upper surfaces of leaves.

When do you decide to control insect pests?
Remember there is no upper limit to look for when considering whether to take action for controlling these pests. Greenhouses are different and the crops grown vary greatly. Growers and their markets also differ in the amount of damage they tolerate. You are therefore encouraged to establish your individual upper limits for these pests based on your own circumstances.

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

The mention of a commercial product does not constitute an endorsement or recommendation by Alberta Agriculture, Food & Rural Development or the Alberta Research Council