Thrips control

Discussion in 'HortForum' started by James Arthurs, Mar 20, 2003.

  1. James Arthurs

    James Arthurs Member

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    I have a thrips infestation. Growing gladiolii is not rewarding, as the flowers are destroyed by this beastie. Suggestions for control (or eradication!) will be welcome.
     
  2. Douglas Justice

    Douglas Justice Well-Known Member UBC Botanical Garden Forums Administrator Forums Moderator VCBF Cherry Scout Maple Society 10 Years

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    Western flower thrips (Frankliniella occidentalis) is a serious pest of a wide variety of greenhouse crops including gladiolus. Thrips stunt growth and cause leaves to become streaked, speckled, papery and distorted and flowers to become blotchy and necrotic as they suck sap from these tissues. Black, shiny specks of excrement deposited on the undersurfaces of leaves indicate a severe infestation.

    Thrips are a very common problem near commercial greenhouse operations. They are difficult to control with conventional insecticides--especially in areas with mild winters, where they reproduce year-round. Successful management depends on the application of a variety of pest control methods.

    Adults overwinter in plant debris or on herbaceous plants inside or outside of greenhouses. Identifying and removing alternate hosts will reduce successive thrips invasions. Infested tissues, such as leaf and flower buds on crop plants (i.e., the plants being directly affected) should also be removed and destroyed. Thrips are weak fliers, and tend to spread to new areas by wind and only slowly on plants.

    A number of natural predators feed on thrips out of doors, including spiders, predatory mites and green lacewings, so conditions that encourage these organisms should be provided. For example, pesticide residues, dust, and dry conditions generally, discourage many beneficials. Diversified plantings that provide a variety of micro-habitats and food sources for beneficials (including, liquid water and nectar sources, shade and protection from larger predators) generally have fewer acute pest problems.

    When the weather is warm, tiny, worm-like larvae feed inside leaves for up to two weeks, then normally drop to the soil and pupate (this is a non-feeding, resting stage when metamorphosis takes place), emerging a week later as winged adults, whereupon they fly back to plants and lay eggs. Females lay from 6 to 10 eggs per day for up to 5 weeks. Eggs hatch in about 5 days.

    In the greenhouse, spreading aluminum foil over the open ground appears to help reduce infestations (probably a combination of physical barrier and light/dark orientation confusion). Increasing humidity may reduce pest populations, as some predators reproduce more reliably under moist conditions. Biological controls for thrips in greenhouses can be purchased from local suppliers. Most of the commercially available bio-control species are unfortunately daylength sensitive and will stop reproducing as the days shorten in late summer (thrips are not affected in the same way). It is therefore extremely important to reduce thrips populations early.
     

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