Thrips
Registered against on 11 crops
Thrips are minute, slender insects with distinctive fringed wings that feed on plant tissue using a rasping-sucking mouthpart. Key pest species in Australian horticultural production include plague thrips (*Thrips imaginis*), western flower thrips (*Frankliniella occidentalis*), onion thrips (*Thrips tabaci*), and chilli thrips (*Scirtothrips dorsalis*). By puncturing epidermal cells and sucking out cell contents, thrips cause surface russeting, silvering, floral blast, and severe fruit scarring.
The economic impact on commercial growers is substantial. Scarring around the calyx or on the skin downgrades premium fresh-market fruit to juice stock or render it unsaleable. In crops like tomatoes, thrips act as vectors for devastating plant viruses such as Tomato spotted wilt virus (TSWV), which can destroy entire stands if left unmanaged.
Where it matters in Australia
Thrips are widespread across all major Australian growing regions. They cause critical cosmetic and yield losses in the pome fruit orchards of the Goulburn Valley and Batlow, citrus blocks in Sunraysia and the Riverland, tropical fruit plantings in Bundaberg and the Atherton Tableland, macadamia orchards in the Northern Rivers, and wine and table grape blocks across southern Australia, alongside field and protected tomato production nationwide.
Symptoms
Direct feeding produces a characteristic 'silvery' or bleached appearance on foliage, often accompanied by small, tar-like black specks of frass. On young fruitlets, feeding near the calyx causes ring scarring, russeting, and scurfy brown patches that expand as the fruit grows.
In flowering crops, heavy feeding causes petal browning, blossom blast, and premature flower drop. On tomatoes, thrips feeding creates 'halo spots' on developing green fruit, while vectoring viruses results in stunted growth, bronze leaf spots, and malformed, unmarketable fruit.
Life cycle
Thrips undergo an incomplete metamorphosis with a egg, two active larval instars, two inactive pupal stages (prepupa and pupa), and adults. Female adults insert eggs directly into soft plant tissues, such as leaves, flower petals, or young fruit skins. Upon hatching, larvae feed aggressively in protected sites like leaf curls, blossom clusters, and under calyxes.
Late-stage larvae drop to the soil, leaf litter, or crevices in the bark to pupate. Warm conditions accelerate development, allowing populations to complete a generation in under two weeks during summer. Adults are highly mobile and easily carried on wind currents, allowing rapid re-infestation of orchard blocks and field paddocks from surrounding weeds or native vegetation.
Monitoring
Begin monitoring prior to spring flush and continue through early fruit development. Deploy yellow or blue sticky traps along block borders and interior rows to monitor adult arrival and seasonal trends. Check traps weekly.
Conduct tap tests by shaking flower clusters, shoot tips, or young fruitlets over a white tray or plastic board to count active larvae and adults. Use a 10x hand lens to inspect beneath fruit calyxes, under leaves, and inside blossoms where thrips aggregate. Record counts in your spray diary to evaluate population trends against established regional thresholds before making control decisions.
Management
Effective control relies on Integrated Pest Management (IPM). Cultural measures include maintaining clean orchard floors and headlands by removing broadleaf weeds that harbour overwintering populations. Avoid slashing flowering inter-row cover crops during peak crop bloom to prevent driving thrips into the main canopy.
Biological control plays a key role; predatory mites (*Neoseiulus cucumeris*, *Montdorensis*), beneficial thrips, pirate bugs (*Orius* spp.), and lacewings provide substantial suppression of larvae. Chemical control should be targeted during sensitive growth stages such as flowering and early fruit set. Always check approved APVMA labels for crop registration, withholding periods, and pollinator warnings. Rotate chemical groups rigorously to mitigate resistance, particularly in western flower thrips populations.
Crops with registered control options
Common questions
- How do I manage thrips resistance during warm summer periods?
- Rotate strictly between different IRAC Mode of Action (MoA) groups across consecutive generations. Avoid back-to-back applications of the same chemical group, and utilize biological controls and soft chemistry early in the season to prevent rapid selection pressure.
- Why are adult counts high on sticky traps when no fruit damage is visible?
- Sticky traps catch flying adults moving into the block, including non-damaging species or migrating plague thrips. Direct beat-testing or tap-sampling of flowers and fruitlets reveals active nymph populations feeding directly on the crop, which correlates better with cosmetic fruit damage.
- What specific label details must be checked prior to flowering sprays?
- Always check the APVMA approved label for pollinator protection statements, flower-stage application limits, withholding periods (WHP), re-entry intervals, and crop-safety warnings regarding russeting or burn on tender foliage.
- How should I interpret the registered product numbers for my crop?
- The product count shows how many APVMA-registered chemical formulations exist for thrips on that specific crop. A larger pool of products provides more active constituents to build robust rotation strategies and manage resistance.
- Does inter-row weed management reduce thrips pressure in orchards?
- Managing flowering broadleaf weeds in mid-rows, headlands, and orchard borders removes overwintering refuges. Slashing or spraying weeds before crop flowering prevents sudden thrips migration into the canopy as weed hosts dry out.
- What is the distinction between direct feeding damage and virus transmission?
- Direct feeding damages surface cells, causing scarring, russeting, or halo spots on fruit. Virus transmission occurs when vector species (such as western flower thrips) infect host plants with pathogens like TSWV during feeding, leading to systemic decline even at low pest densities.