Thunderbug: A big challenge for greenhouse growers

Thrips are a major pest of horticultural greenhouse plants in Ontario. A number of thrips species are commonly found including Western Flower Thrips (Frankliniella occidentalis), Eastern Flower Thrips (Frankliniella tritici), Onion Thrips (Thrips tabaci), and Echinothrips. The adult and larval stages feed by piercing the plant surface with their mouthparts and sucking out the contents of plant cells. This causes a variety of problems such as: a) Petal streaking/distortion aka "color break", b) Calyx damage, c) Fruit streaking/curling/spotting, d) Premature leaf drop, and e) Discolored and rolled terminals.

Written by: Dr. M. Ishtiaq Rao, Crop Defenders Ltd.

In addition to feeding damage, ­­­Western flower thrips are an important vector of Tospoviruses. This has serious implications, as Impatiens necrotic spot virus and Tomato spotted wilt virus can severely damage or kill certain vegetable and ornamental crops.

Thrips damage on pepper, causing speckling

Thrips damage on tomato

Monitoring thrips is important for effective pest control regimes. Adult thrips can be monitored by hanging bright blue sticky traps in or near host plants. Use 1 trap per 200-500 m2. Traps should be checked weekly and the average number of thrips per trap should be recorded. The average calculated will help when making decisions about what pest control options to use, when to apply them, and what quantity is necessary.

Thrips damage on cucumber, causing fruit curl

Thrips (left), being attacked by N. cucumeris (right)

Thrips are a difficult target to control, they are resistant to most pesticides and feed deep within the flower head or on developing leaves. Biological control provides a number of options for reducing populations of the different life stages of thrips:
a. Neoseiulus cucumeris and Amblyseius swirskii control western flower thrips by feeding on the first instar larvae. A. swirskii can also feed to a lesser extent on second instar thrips. However, they cannot completely eliminate a thrips population.

b. Orius is effective in controlling thrips because it feeds on all stages of thrips.
a. It is often found in the flowers, because pollen is its alternative food source. Since pollen is not often present in ornamental crops, Orius is not as effective in flower crops as it is in vegetables.

b. For greenhouse vegetable crops, Orius is most successfully used on peppers and cucumber.

c. Recent research has shown ornamental peppers can be used as a banker plant for Orius in other crops, allowing a population to establish, develop and disperse within the greenhouse.
c. Stratiolaelaps scimitus and Gaeolaelaps gillespiei are soil-dwelling predatory mites that feed on a variety of soil organisms, including thrips pupae. Research has estimated they can kill up to 30% of thrips pupae.

d. Metarhizium anisopliae or Beauveria bassiana are fungal pathogens of thrips. It can be either sprayed onto the crop or distributed via bumblebees that are supplied with hives specially equipped with dispensing trays. These trays contain B. bassiana spores, and the bees must walk through the trays to leave the hives. In the process, some of the spores stick to their bodies. The spores become distributed in the crop when the bees pollinate the crop's flowers. When thrips come into contact with spores on the crop surface, they become infected and die.

e. Rove beetles, predatory thrips, and green lacewings also help to control thrips.

Orius killing a thrips

Dr. M. Ishtiaq Rao, Business Manager & Entomologist at Crop Defenders Ltd.

For more information:
Crop Defenders
Dr. M. Ishtiaq Rao, Ph.D.
Business Manager
150 Fraser Road, Leamington ON N8H 4E7 Canada
phone: +1 866-300-2929
fax:+1 519-250-4972

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