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Thrips

Thrips

Order Thysanoptera

insect

In a Nutshell

    Small silver patches appear on the upper side of leaf blades, an effect known as silveringYellow, black or fasciated, insects of 1-2 mm in length and black dung spots on underside of the leavesDeformation of leaves, flowers and fruits

Hosts: %1$s

· Apple · Pear · Grape · Raspberry · Gooseberry · Bean · Capsicum & Chili · Eggplant · Cherry · Apricot · Peach · Carrots · Turnip · Pea · Cucumber · Pumpkin · Zucchini · Tomato · Cabbage · Lettuce · Potato · Gram · Pigeonpea · Oat · Triticale · Cotton · Additional · Spinach · Chard · Onion · Garlic · Leek · Maize · Strawberry · Blackberries · Currant · Radish · Sweet Potato · Peanut ·

Symptoms

Larvae and adults feed on plant tissues and produce small silver patches on the upper side of leaf blades, an effect known as 'silvering'. The same patches can appear on petals where the pigment has been removed. On the underside of the leaves, the thrips and their larvae sit together in groups alongside their black dung spots. Leaves of affected plants yellow, wither, deform or shrivel. Feeding during bud or flower development later results in scarred, stunted or deformed flowers or fruits respectively and loss of yield.

Trigger

Thrips are 1-2 mm long, yellow, black or fasciated insects. Some varieties have two pairs of wings, others do not have wings at all.They hibernate in plant residues or in the soil or on alternative hosts plants. They are also vectors for a broad range of viral diseases. Dry and warm weather conditions favor population growth. Humidity reduces it.

Biological Control

Some biological control measures have been developed for specific thrips. Predatory mites that feed on larvae or pupae are commercially available. Against varieties that attack the leaves and not the flower, try neem oil, especially on the undersides of the leaves. Spinosad application is generally more effective against thrips than any of the chemical or other bioclogical formulations. It lasts 1 week or more and moves short distances into sprayed tissue. It can however be toxic to certain natural enemies (e.g., predatory mites, syrphid fly larvae) and bees. Do not apply spinosad to plants that are flowering. In case of flower thrips infestation, some predatory mites or green lacewing larvae could be used. A combination of garlic extracts with some insecticides also seem to work well. Use of highly reflective UV mulch (metalized mulch) has been recommended.

Chemical Control

Always consider an integrated approach with preventive measures together with biological treatments if available. Due to the high reproductive rates and their life cycles, thrips have developed resistance to different classes of pesticides. Effective contact insecticides include azadirachtin, insecticidal soaps, narrow-range oils and pyrethrins, which many products combine with piperonyl butoxide.

Preventive Measures

    Plant resistant tomato varieties (several on the market)Resistant varieties generally do not require insecticide applications for thrips to control tomato spotted wiltUse virus- and thrips-free transplants from greenhouses that manage thrips and inspect transplantsUse sticky traps over a large area for mass-catchingAvoid planting near alternative hosts or plants infected with the virusGreenhouses could be sterilized with steam between plantingsMonitor for thrips and tomato spotted wilt symptomsControl weeds in and around the fieldRemove infected plant and any plant debris and destroy itKeep plants well irrigated, and avoid excessive applications of nitrogen fertilizer