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Western flower thrips (WFT) insecticide resistance management plan

Date: 01 Jul 2012

Introduction

This guide provides information to assist in decision making for control of western flower thrips (WFT) in capsicums; cucumbers; culinary herbs; eggplant; lettuce; ornamentals; parsley and coriander; silverbeet; spring onions and shallots; stone fruit; strawberries; tomatoes; and snow peas and sugar snap peas. It includes:

notes on managing WFT;
methods to detect WFT;
strategies for application of sprays;
the selection of available chemicals approved by the APVMA.

WFT can cause damage to crops by feeding on them, and can spread tomato spotted wilt virus (TSWV) in crops.

Insecticides alone are not enough to beat WFT. The following cultural control advice should be used, together with a chemical strategy, to effectively manage WFT, and avoid infections of TSWV.

Important
WFT is a pest that readily acquires resistance to insecticides. For this reason it is important to avoid dependence on a single chemical.

It is also important that growers make their own judgment as to the suitability, effectiveness and safety of the chemicals for the intended use, and the effect that use of the chemical may have on trade, and do so at their own risk.

Always read the label
Users of agricultural (or veterinary) chemical products must always read the label and any Permit before using the product, and strictly comply with the directions on the label and the conditions of any Permit. Users are not absolved from compliance with the directions on the label or the conditions of the Permit by reason of any statement made or not made in this publication.

Effects of WFT and TSWV on selected crops

Crop	Effects of WFT	Effects of TSWV
Capsicums	Silvering on surface and corkiness under the calyx. Ghost spotting more rarely.	Shirting and tip yellowing of plant. Multi-coloured ringed fruit.
Cucumbers	Deformities including curled fruit and silvering on leaves.	Does not show symptoms in cucumbers, but can be spread to other crops.
Lettuce	Scarring on leaf undersides.	Wilting of leaves. Browning of tissues.
Ornamentals	Scarring, silvering, flecking, distortion.	Effects are crop-specific.
Stone fruit	Silver russetting on fruit in the weeks just prior to harvest. Deformed fruit resulting from WFT feeding during fruit formation.	Stone fruit are not affected by TSWV.
Strawberries	Russetting on fruit surfaces or around seeds. Other symptoms that look like frost damage, boron deficiency or sun scald.	Strawberries are not affected by TSWV.
Tomatoes	Silvering on lower leaves. Occasionally scarring on fruit.	Wilting and bronzing of leaves. Yellow splotches or concentric rings on ripe fruit.

Keep your farm clean!

Remove or control weeds within and nearby your crop/orchard, because weeds harbour WFT that will reinfest your crop/trees.
Plough in or burn old crop debris.
Remove unwanted flowers or plants affected with TSWV, and burn or bury.
Monitor for WFT in your crop/orchard and packing sheds with sticky traps.
Only buy WFT and TSWV-free seedlings/cuttings/runners from a reliable or accredited supplier, otherwise large losses can occur.
Don’t bring any plant material onto your property unless necessary, because you may bring WFT with it. Keep any deliveries to one side and inspect for WFT. If found to be present, return the affected plant material to the supplier, or burn or bury it.
Try to control WFT when plants are young, to prevent high levels of TSWV in your crops/orchard.
Try to manage WFT well before harvest.
Use insect-proof screening on your greenhouse if your crop is grown under cover.
Avoid carryover crops if possible, as they may be more severely affected by WFT/TSWV.
Important: Once harvesting has commenced, it may be difficult to follow the insecticide usage plan recommended in this information, and also observe withholding periods.
Be familiar with the natural enemies of WFT present on your farm, and where possible choose pesticides with the least impact on them.

Monitoring for WFT

It is important to monitor your crops or orchard to check if WFT is present because it can easily be confused with other less damaging species of thrips. Monitor using yellow sticky traps and crop/orchard inspections.

Seek help from NSW Department of Primary Industries or your State Department of Agriculture / Primary Industries for identification of WFT.
Yellow sticky traps should be hung just above the crop, or within the crop for stone fruit (about 3–10 traps per hectare, or one trap per 200 m² in greenhouses).
You should check for WFT on sticky traps and walk through your crops/orchard looking for thrips at least twice a week. Keep records.
It is also a good idea to tap some flowers over a white tray or yellow sticky trap and collect any thrips in spirits (e.g. methylated spirits) for identification by the NSW Department of Primary Industries, or your State Department of Agriculture / Primary Industries.
If WFT are numerous or increasing in number you should consider applying insecticides as described below before damage occurs.
Be aware of action thresholds in each crop type.
It is important to only apply insecticides if needed because the more often they are applied, the greater the chance that WFT will become resistant to them.

Spraying

Adult and larval stages of WFT can be effectively killed by insecticides, but the eggs (laid inside leaf tissue) and pupae (mostly in soil) are protected from sprays. (See the diagram below of the life cycle of WFT.) For this reason three sprays are recommended to cover the time taken for eggs to hatch into larvae and for pupae to develop into adults.

A series of three sprays of the same chemical a few days apart will be effective for killing the majority of thrips.

The interval between applications varies with temperature. In cooler regions or at cooler times of the year (10°C–20°C) the length of the lifecycle is 25–35 days. At 20°C–30°C the life cycle is 15–25 days. Therefore, the higher the temperature, the shorter the interval between sprays. Make 3 consecutive applications at either 3-5 day intervals when temperatures are greater than 20^oC or at 6-12 day intervals when temperatures are less than 20^oC.

Important note on applying consecutive sprays, and chemical resistance
Reduce the chance of WFT becoming resistant. Apply three consecutive sprays of the same chemical and then alternate to a different chemical group for the next series of sprays. There must be at least a 3 week break (<20°C) or a 2 week break (>20°C) before another series of sprays is applied. If monitoring indicates the need to spray earlier, then insecticide resistance, inappropriate spray application or inadequate farm hygiene should be suspected, and expert advice sought.

Follow product label directions for the minimum interval between successive applications.

If you need to spray again

You should continue to monitor numbers of WFT so you know when to apply another series of sprays. If WFT are building up on sticky traps or you see many WFT on your plants, or fresh damage is visible then consider spraying again.

However, if the same insecticide is always used to control WFT, the thrips will become resistant and the chemical will no longer be effective. Superscript in Table 1 indicates possible resistance already present in the WFT population.

Approved chemicals

Chemicals approved by the APVMA for off-label use, and chemicals registered for use against thrips or WFT, in:

N.B. To see all chemical control possibilities see both generic and specific listings, e.g. berry fruit and strawberry; leafy vegetables and lettuce.

Further information

For more information about WFT see the Thrips section of the NSW DPI website.

Author: Grant Herron, Marilyn Steiner, Bettina Gollnow, Stephen Goodwin