Thrips

Members of the Thysanoptera order, the term 'thrips' includes more than 6,000 species. They can become serious pests in indoor, outdoor and greenhouse settings. In general, thrips are not host plant specific; however; species such as onion thrips and tobacco thrips feed on plants in specific families. Thorough trapping and regular inspection is the first and biggest step to take towards controlling thrips.

Life Cycle:

Their life cycle consists of five life stages: egg, larvae, prepupae, pupae and adult. The full cycle can take up to 30 days to complete, but will shorten in higher temperatures. Adult thrips lay their eggs directly into plant tissue giving them a place to overwinter come fall and a hatching location surrounded by food sources for the larvae. Once hatched, the larvae feed voraciously on new growth as they prepare to drop to the soil and pupate. After feeding as larvae, thrips develop into their prepupal and pupal stages from which they hatch into wingless nymphs. The nymphs molt two or more times and become winged adults ready to mate. Thrips can go through as many as 12-15 generations per year in warm climates.

Damage:

Adult and larval stages of thrips feed on foliage and flowers causing extensive damage in a short time period under the right conditions. Damage typically shows up as stippling, silvering of the leaves, or discolored patches on the leaf surfaces, but can also be identified by the unique twisting they cause in new growth. Discarded pollen and frass can also be a major issue for orchid, violet and other ornamental growers as the buildup is unsightly and reduces flower longevity. Proactive control is important to limit risk of thrips vectoring disease through feeding.

Thrips Control:

  1. Monitor plants early and often for signs of thrips activity or damage.

    • If you suspect thrips have come into your growing area, gently shake foliage/flowers over a piece of white paper to knock some of them off for closer inspection.
    • Hang Blue or Yellow Sticky Traps within the growing area to monitor pest populations. Blue traps are best when beneficial insects are already present.
  2. Biological controls should be used if the infestation is moderate or minimal to reduce impact on the environment. Many insects control thrips at various life stages and there are numerous mycoinsecticides that target thrips.

    • General predators can keep thrips populations at low levels limiting damage. Generalists include green lacewing, ladybugs and minute pirate bugs (Orius insidiosus).
    • Neoseiulus cucumeris are predatory mites used for thrips prevention, control and continued management. They feed on immature thrips and multiple species of mites. For best results, release before thrips become a serious issue as establishment can take 6-8 weeks.
    • Stratiolaelaps scimitus feed on a number of soil-dwelling pests including thrips prepupae and pupae.
    • Amblyseius swirskii can also be used as a thrips control measure, but are primarily mite predators.
  3. Use insecticides for early knockdown or as a last resort to control infestations that beneficial insects cannot.

    • Neem oil is an effective knockdown spray and can be used prior to releasing beneficial insects. It also suppresses foliar disease growth.
    • Azadirachtin sprays work as feeding/growth inhibitors and can be combined with pyrethrins to increase impact and coverage.
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