Controlling Thrips In Your Garden

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There are more than 6,000 thrips species sucking the life from plants all over the world. Get rid of them naturally without resorting to toxic sprays by using these SAFE, organic methods.

Identification:

Most adult thrips are elongate, slender, minute (less than 1/20 inch long), and have long fringes on the margins of both pairs of their long, narrow wings. Immatures (called larvae or nymphs) are oblong or slender and elongate and lack wings.

Life Cycle:

Thrips hatch from an egg and develop through two actively feeding larval stages and two non-feeding stages, the prepupa and pupa, before becoming an adult. Late-instar larvae change greatly in appearance and behavior and are called prepupae and pupae, even though thrips do not have a true pupal stage.

Damage:

Thrips feeding on plants can damage fruit, leaves, and shoots and very noticeably affect plants’ cosmetic appearance. However, thrips rarely kill or threaten the survival of trees and shrubs. Herbaceous ornamentals, and certain vegetable crops, are more susceptible to serious injury from thrips feeding and thrips-vectored viruses, especially when plants are young.

Management:

Thrips are difficult to control. If management is necessary, use an integrated program that combines the use of good cultural practices, natural enemies, and the most selective or least-toxic insecticides that are effective in that situation.

Monitoring:

If thrips are a suspected cause of plant damage, thrips adults and larvae can be monitored by branch beating or gently shaking foliage or flowers onto a light-colored sheet of paper, beating tray, or small cloth.

For thrips that feed in buds or unexpanded shoot tips, clip off several plant parts suspected of harboring thrips, place them in a jar with 70% alcohol (ethanol), and shake vigorously to dislodge the thrips. Strain the solution through filter paper so thrips can more readily be seen.

Biological Control:

Predatory thrips, green lacewings, minute pirate bugs, mites, and certain parasitic wasps help to control plant-feeding thrips. To conserve and encourage naturally occurring populations of these beneficials, avoid creating dust and consider periodically rinsing dust off of small plants, avoid persistent pesticides, and grow a diversity of plant species.

Cultural Control:

Thrips species that feed on many different plant species often move into gardens and landscapes when plants in weedy areas or grasslands begin to dry in spring or summer. Avoid planting susceptible plants next to these areas, and control nearby weeds that are alternate hosts of pest thrips. Grow plants that are well-adapted to conditions at that site.

Pruning:

Prune and destroy injured and infested terminals when managing a few small specimen plants in the landscape. Avoid shearing plants, which is the clipping of dense foliage to maintain an even surface on formal hedges or creating specific shapes (topiary).

Shearing stimulates thrips-susceptible new growth. Prune by cutting plants just above branch crotches and nodes instead of shearing off terminals.

Row Covers:

Row covers, hot caps, and other types of cages with a fine mesh can exclude thrips and other insects from vegetables and other young herbaceous plants. Apply row covers before crops emerge or to pest-free plants during planting. Plants are normally covered or caged only while they are young and most susceptible to damage. Once plants become larger or temperatures get warmer, remove covers to provide enough growing space and to prevent overheating. Drip or furrow irrigation is generally necessary when using row covers.

Greenhouse Thrips Management:

Greenhouse thrips can infest many plant species but primarily is a pest of evergreen, broadleaved perennials. It occurs mainly on the underside of leaves and on fruit clusters or other plant parts that touch each other. Greenhouse thrips is sluggish and the adults tend not to fly.

Individuals feed in groups and populations usually begin in a limited part of the plant and spread slowly. If the underside of leaves on susceptible plants are regularly inspected to allow early detection and removal of new infestations, pruning off colonies can be effective.

Insecticides to Avoid:

The systemic organophosphate acephate (Lilly Miller Ready-to-Use Systemic, Orthene) is available for ornamental, nonfood plants. Avoid using it. Acephate can be highly toxic to natural enemies and pollinators and can cause spider mites to become abundant and damage plants after its application.

Insecticides More Toxic to Thrips and Beneficial Insects:

Systemic insecticides are absorbed by one plant part (e.g., roots) and moved (translocated) to other plant parts. Trunk spray or injection of an effective, systemic, neonicotinoid insecticide can provide relatively rapid control. With soil drench or injection, there is a longer time delay between neonicotinoid application and insecticide action.

Chemical Control:

Although thrips damage is unsightly, it does not usually warrant the use of insecticides in gardens and landscapes. Feeding injury typically does not become apparent until after tissue grows and expands. Thus, by the time damage is noticed on ripening fruit or distorted terminals, the thrips that caused the damage are often gone.

Insecticides Most Compatible with IPM:

Contact insecticides that do not leave persistent residues can be effective for greenhouse thrips and other species that feed openly on plants. These products have low toxicity to people, pets, and pollinators and relatively little adverse impact on biological pest control; because they do not leave toxic residues that would kill natural enemies migrating in after their application.