Insect pest management in sunflowers
On this page:Establishment pests
- False wireworms
- True wireworms
- Black scarab beetles
- Wingless cockroaches
- Black field earwigs
- Field crickets
Sunflowers are attacked by a number of insect pests at various stages of crop development. Most pests are not specific to sunflowers and originate from other crops, weed hosts or plant residues in the soil.
Several species of soil-dwelling insects attack seeds and seedlings of sunflowers, causing thinning or complete destruction of plant stands. Sunflowers are more susceptible to seedling damage than other field crops because damaged sunflower seedlings lack the capacity to regrow or tiller. Seedlings are most vulnerable to damage:
- before they develop three to four ´true´ leaves
- during periods of moisture stress
- when other factors such as low soil temperature or soil compaction limit plant growth.
Once sunflowers have established, a number of other pests can attack the crop. Of these only the Rutherglen bug and helicoverpa are considered serious and require monitoring.
Striate false wireworm (Pterohelaeus alternatus), Eastern false wireworm (Pterohelaeus darlingensis), Southern false wireworm (Gonocephalum macleayi)
- both adults and larvae attack sunflower
- larvae feed on decaying vegetable and crop residues in the soil
- they also feed on newly germinating seed and the growing points of seedlings which results in patchy stands
- damage is most common in early-planted crops where crop residue has become scarce
- during summer, adults may damage young plants by surface feeding or cutting of the plant at or near soil level
- damage by both larvae and adults may necessitate replanting.
Larvae are more damaging in southern Queensland whereas adults are the most damaging stage in central and northern districts.
The risk from adults is highest in summer. For larvae the risk is highest for early (September-October) planted crops. Damage may occur if early plant growth is slowed by cool, damp weather allowing larvae to remain in the moist root zone. As soil dries they retreat below the root zone. However, if crops are grown into dry seedbeds, damage may be significant.
Monitoring and thresholds
- Detection can be difficult - either hand sift 10 soil samples (30 x 30 cm) or place 10 germinating seed baits (GSB) monitoring for soil-dwelling insects throughout the paddock.
- One larvae per sample warrants control.
High mortality of false wireworms can be caused by cool, wet weather from autumn to spring.
False wireworm beetles are more damaging to sunflower seedlings where stubble is buried by cultivation than in crops that are directly drilled into the surface retained stubble. This is because the surface feeding beetles remain feeding on the stubble and not the crop.
- Prepare ground for even and rapid germination.
- Use of press wheels at planting provides some control.
- Clean cultivation during summer dries out topsoil and eliminates weeds that provide food for adults.
- Larvae can be controlled by insecticide applications at planting or insecticide-treated seed.
- Control of adults is obtained by baiting with insecticide-treated cracked grain broadcast evenly over the surface at or immediately after planting.
- Where broadcasting is not possible, the bait may be laid in trials spaced no more than two metres apart.
- Natural enemies provide little control.
True wireworms (Agrypnus spp)Wireworms are named for the supposed wire-like appearance of their larvae. True wireworm adults are elongated beetles that jump and click when disturbed.
Larvae are similar to false wireworm larvae. They may also be mistaken for predatory larvae of other beetles.
- Larvae bore into germinating seed and chew on seedling roots and shoots resulting in reduced vigour or seedling death.
Monitoring and thresholds
- Use GSB or soil sampling to detect larvae prior to sowing. Monitor crops after sowing until establishment.
- One larvae per GSB warrants control.
- Seed dressings, in-furrow sprays and granular insecticides offer some control.
- Cutworm larvae can sever stems of young seedlings at or near ground level, thereby causing collapse of the plant.
- Sometimes the young plant is partially dragged into the soil where the larvae feed on it.
- Larvae may also climb plants and browse on or cut off leaves.
- Crop areas attacked by cutworms tend to be patchy and the destruction of seedlings in one area may cause cutworms to migrate to adjacent fields.
- Risk period is summer and spring - one generation per crop.
Monitoring and thresholds
- Inspect emerging seedlings twice a week and plants up to budding stage once a week.
- Treat seedlings when there is a rapidly increasing area or proportion of crop damage (more than 10% seedling loss).
- Treat older plants if more than 90% of plants are infested or more than 50% of plants have 75% or more leaf tissue loss.
- Cutworms are attacked by a range of natural enemies such as:
- common brown earwigs
- orange caterpillar parasite
- two-toned caterpillar parasite
- orchid dupe
- Controlling weeds prior to planting will reduce cutworm infestations.
- Chemical control may be cost effective. Spot spraying of identified patches may suffice. Spray late afternoon, close to feeding time, for best results.
At least two species of black scarabs attack sunflowers. Their lifecycle on sunflowers is one generation per year with the adults damaging the crops in summer.
- Larvae feed on taproots causing wilting and death of seedlings.
- Adult beetles can defoliate and kill plants up to 40 cm tall.
- Adults often feed in a line across the field.
- Beetles hide in the soil during the day and emerge in late afternoon to feed
Monitoring and thresholds
- Check in the soil by digging and sieving for the presence of larvae prior to planting, and at all stages for adults.
- Look for feeding beetles just before sunset.
- Four beetles per square metre can cause severe losses to young seedlings and may warrant control.
- Removal of the host parthenium weed is advised.
- Limited control can be achieved by spraying either side of the feeding line.
- Spray when beetles are active on the soil surface.
- Chemicals are registered but of limited effectiveness.
- Beetles can also be controlled by application of pelleted baits (alfalfa or similar meal) at planting. Cracked grain baits do not control beetles.
- Damage is most prevalent where sunflowers follow wheat, sorghum or grass pasture.
Thrips are most abundant during a hot, dry spring following a mild dry winter.
- Both adults and nymphs feed on the leaves by rasping the surface tissues and sucking the exuded juices.
- Damage is normally insignificant, however when there are high populations of thrips on seedlings, they cause distortion and browning of the cotyledons and leaves.
- Under these conditions seedlings can become stunted and die.
- Thrips are an important vector for the pathogen tobacco streak virus (TSV).
- If needed insecticides can be used.
- If a decision is made to control thrips, apply a narrow band spray over the seedlings to preserve predators such as spiders in the inter-row.
- Thrips may require control in areas of known TSV outbreaks.
- Cockroaches are mainly a problem where seedlings are present in late summer and autumn.
- On small seedlings, they feed on cotyledons and stems, often severing the stem.
- On larger seedlings, they feed on the leaves and growing points.
Monitoring and control
- Nymphs and adults are found under stubble but congregate around volunteer plants in bare fallows.
- If the soil surface dries they tend to move down to the moist soil layer.
- They feed at night and shelter under trash by day.
- They pose the highest risk where seedlings are present.
- Populations reach the highest densities under no tillage with stubble retained.
- Determine numbers with GSB.
- Take action when there are one or more cockroaches per two GSB.
- Use insecticide-treated seed. See chemical control options.
- A parasitic fly has been recorded parasitising nymphs but parasitism percentages are low (under 5%).
Black field earwigs are a sporadic pest of sunflowers.
- Eat newly sown and germinating seed and the roots of crops below ground, resulting in poor establishment.
- Chew the stems of newly emerged seedlings above ground.
Monitoring and control
- Use GSB or digging and sieving to detect adults and nymphs prior to planting.
- Monitor crops after planting until establishment.
- Control if more than 50 earwigs in 20 GSB.
- Grain baits containing insecticide applied at sowing offer best protection.
- Insecticide seed dressings provide some protection.
- In-furrow sprays are not effective in protecting against dense populations.
- The black field earwig is mainly a pest in areas having heavy, black soils.
- Earwigs prefer cultivated soils rather than undisturbed soil (zero til).
- Use press wheels at sowing.
Black field crickets (Teleogryllus spp), brown field crickets (Lepidogryllus spp)
Minor, widespread and irregular pests of sunflowers.
- Feed on the leaves and stems of seedlings.
- Sometimes sever the stem at or above ground level.
- They may also attack more mature plants - feeding on the back of flower heads and on the maturing seed on the face of the head.
Monitoring and thresholds
- Crickets feed at night - inspect crops at dusk when crickets are most active.
- Black field cricket activity can be monitored with light traps.
- One or more crickets per two GSB require control.
- Use GSB to determine cricket numbers.
- Field crickets are controlled using insecticide-treated cracked grain baits.
- Control can be achieved with insecticide-treated grain baits.
- Weedy cultivation prior to planting may encourage crickets.
- Natural controls like disease, parasitic insects and predators such as birds have little impact on crickets.
- Nematodes are common parasites of brown field crickets in Central Queensland.
- Cricket populations are regulated by weather conditions.
Post-establishment pestsRutherglen bug (Nysius vinitor), grey cluster bug (Nysius clevelandensis)
The Rutherglen bug (RGB) is a major, widespread pest of crops throughout Australia. Grey cluster bug is a minor pest of sunflowers in Queensland and northern New South Wales. RGB is the most damaging insect pest on sunflower.
Bugs can often appear in large numbers in a very short time and only in occasional seasons. Their invasion is unpredictable as they can migrate 200-300 km in a single night.
Populations of RGB in cropping areas will breed on weeds, moving to available crops or weeds when hosts die off. Adults fly into crops while flightless nymphs move by walking.
In seasons when RGB is a major pest, the population is dominated by migrants from outside the local cropping areas which are carried from inland breeding sites to eastern cropping regions. Depending on the time of planting, adults may be present during budding and flowering and nymphs post-flowering. During summer, several overlapping generations develop in which all stages may be present.
- Winter and spring conditions that favour prolific weed growth followed by a dry late spring will force bugs off their host plants onto crops.
- Adults congregate on the stems during budding and cause the head to wilt, become malformed or die.
- After flowering adults lay eggs in flower heads and both adults and nymphs feed on the seed, reduce grain yield, oil content, oil quality and reduce seed germination.
- Damage is higher in moisture stressed crops.
- Damage can occur until harvest depending on seed hardness.
The critical times to monitor for RGB are at budding and seed fill.
To monitor for bug numbers - count adults on buds and heads at weekly intervals.
- Budding: bugs congregate on the upper stem and bud.
- Flowering: eggs are laid between individual flowers with nymphs emerging after about seven days to feed on the young seeds.
Thresholds (adult bugs per plant)
August to December
January to April
*The threshold is lower for confectionary sunflower due to the need to meet human consumption specifications. Brown marks on the seed from piercing make confectionary seed visually unattractive.
Understanding the lifecycle of RGB is helpful when making spray decisions. The aim is not to allow adults to breed as population explosions will then occur. Adults will not start breeding until a protein source is available (i.e. developing sunflower seed). Adults stop breeding in late February.
- Remove host weeds and by ploughing a deep furrow around the crop, prevent wingless bugs from migrating from weeds.
- If crops require spraying, best results are achieved before heads turn down to the ground.
- The most effective pesticides have limited residual effect and severely disrupt natural predator populations.
- As adults are winged, re-infestation can occur rapidly after treatment. Multiple treatments are sometimes required.
- Sprays are best applied at the end of flowering (petal fall) when adults begin to lay eggs. This timing will normally prevent subsequent nymphal populations developing.
- Spray late afternoon when bees are less active.
Egg parasitoids (Telenomus spp.) are sometimes important in hindering or preventing nymph infestations and reducing bug populations. Their potential contribution to population control will be limited in seasons when there are large influxes of adults. More than one species of egg parasitoid has been found. Parasitism of eggs is generally low with the maximum recorded at 33.3%. Predation has rarely been recorded, but spiders may play a role.
There are two important helicoverpa pests of sunflowers - the native budworm Helicoverpa punctigera and the corn earworm H. armigera. They usually occur from late budding until late seed fill.
The proportion of each species found on sunflower depends on the time of planting in any particular year and also from year to year.
Although damage from helicoverpa is obvious and appears serious, they are not considered of major economic importance in sunflowers as the plant is able to tolerate large infestations and still produce a worthwhile yield.
- Caterpillars feed on the leaves, buds and petals or on the small green bracts surrounding the head.
- Damage to the developing seed is of little consequence unless infestations are very heavy.
- Feeding on the back of the head can predispose the crop to secondary head rots.
- Stressed dryland crops are more prone to head rots than unstressed irrigated crops.
- Heavy infestations during bud stage can result in severe damage.
- Larval feeding can cause deformation of the seed head and sometimes loss of the head by larvae chewing into its connection with the stem.
Monitoring and thresholds
- Budding is the most vulnerable stage as the whole bud can be eaten. Populations of one medium or two small larvae/plant warrant control.
- Natural mortality rates of 30% for larvae less than 5 mm in length should be taken into account.
- At flowering to grain fill stage, the plant is able to tolerate larger populations.
- Damage to the back of the head may predispose the head to rot but this is rarely an economic reason to control helicoverpa due to the many other causal insects.
- At the bud stage, the caterpillars are concealed within the bud bracts and are difficult to control with insecticides.
- When spraying is necessary, it is best to wait until the buds are just beginning to open and the yellow petals are becoming visible.
- Spraying earlier may result in poor control while spraying later can affect pollination by bees.
- Control is normally only warranted before the heads turn down.
- Helicoverpa have a large number of natural enemies such as egg and larval parasitoids, predators and various diseases. Parasitism can at times exceed 30%.
- Helicoverpa armigera larvae are best targeted when smaller than 5-7 mm.
The requirement for insecticide treatment in the post-flowering stage for the control of larvae in sunflower remains problematic. Trial results suggest that an initial population averaging 17 larvae/plant during the post-flowering stage of crop development caused no significant reduction in yield in the absence of secondary head rots. Insecticide spraying is unlikely to reduce head rots.
Greenhouse whitefly (Trialeurodes vaporariorum)
Greenhouse whitefly is a sporadic pest of sunflowers.
- Nymphs and adults suck sap and excrete honeydew.
- A secondary infection develops when a black sooty mould fungus grows on the sticky honeydew.
- There are no visible damage symptoms with low numbers of whiteflies.
- Under very heavy infestations, plants lose vigour and damage is manifested under severe moisture stress, causing leaf wilting and failure to set seed.
- There are no insecticides registered for the control of whiteflies on sunflower.
- An introduced parasitoid is widespread in Australia and commonly attacks whitefly nymphs.
- Consider that chemicals targeting other pests can affect parasitic wasps which provide effective control of whitefly.
Bemisia tabaci whitefly complex
The Bemisia tabaci species complex is represented in Australia by three distinct biotypes: Australian Native (AN), silverleaf whitefly (SLW) or B biotype, and Q biotype .
The Australian native (AN) is quite common but causes no problems. The B biotype was first discovered in Australia in 1994. It is a pesticide-resistant strain that came from overseas (most likely the United States). The Q biotype was reported from Australia in early 2009 and its distribution is yet to be determined. The Bemisia tabaci biotypes in Australia are morphologically indistinguishable and can only be distinguished using chemical (enzyme) or DNA techniques.
Hosts of the B and Q biotypes include at least 500 crops and ornamental plants worldwide and it is a pest on many.
During the 2001-02 season large populations of B biotype were found on sunflowers in Central Queensland. However, infested sunflower crops suffered little damage.
- B biotype are usually found on the lower leaf surface and they affect all crop stages.
- B biotype have a high reproduction rate and a short generation time and the large numbers generated can retard plants simply through feeding.
- The insect secretes large quantities of honeydew that interferes with photosynthesis and can reduce plant vigour.
There are no registered insecticides for whiteflies in sunflowers. Cultural control options include:
- breaks in the cropping cycle
- elimination of alternative hosts
- conservation of natural enemies.
- Parasitic wasps commonly provide some level of biological control. Predators include big-eyed bugs, green lacewing larvae, brown lacewing larvae and ladybird beetles.
- Natural enemies can provide good control of whitefly and stabilise populations as long as they are not disrupted by the overuse of non-selective insecticides.
Loopers are an occasional pest of sunflower and can be distinguished from helicoverpa by:
- their 'looping' action when walking
- by their body, which tapers towards the head
- they have only two pairs of hind legs, as opposed to four for helicoverpa.
- Larvae feed on leaves.
- Tissue damage is insignificant when larvae are small but increases with larger loopers.
- Large irregular shaped holes in the leaves usually coincide with the appearance of large larvae.
- Severe defoliation is uncommon.
- Looper infestations are often controlled by parasitoids, predators and diseases before they cause too much damage.
- Control is usually unwarranted but caterpillars causing severe damage late in crop development can be controlled with insecticides if warranted.
- Crops should be scouted for looper eggs and moths to pinpoint the start of infestations and to increase the chance of success of biopesticides such as Bacillus thuringiensis (Bt).
- Loopers appear susceptible to all insecticides used for helicoverpa control, with the exception of Gemstar and VivusMax (Helicoverpa nucleopolyhedrovirus (NPV)) which only act against helicoverpa.
- Dipel (Bt) is far more effective against loopers than against helicoverpa but thorough coverage is required for best results.
- GVB have a wide host range and cause damage by sucking sap.
- GVB tend to feed on the upper stems and heads and when present in large numbers, cause shrivelling, wilting and deformed heads.
- If they gather around the peduncle, water and nutrient supply to the developing head will be reduced.
- They occasionally feed on developing seed.
- The current threshold is one mature bug or 5th instar nymph/plant.
- Chemical control is warranted if large populations of GVB are present.
- GVB eggs are frequently parasitised by a tiny introduced wasp Trissolcus basalis (green vegetable bug egg parasite). Parasitised eggs are easily recognised as they turn black. Parasitised GVB eggs may be confused with eggs of the predatory shield bugs but lack the spines that ring the top of the eggs of these species.
- GVB nymphs are attacked by ants, spiders and predatory bugs. Final (5th) instar and adult GVB are parasitised by the recently introduced tachinid fly, the green vegetable bug parasitic fly (Trichopoda giacomellii).
Registered insecticides and current recommendations for insect control on sunflowers are available from the Australian Pesticides and Veterinary Medicines Authority.
The Department of Employment, Economic Development and Innovation (consisting of several former agencies, including the Department of Primary Industries and Fisheries) publications:
- Department of Primary Industries 1985, A Handbook of Plant Diseases in Colour: field crops (2nd edn), QI85016.
- Swaine GA and Ironside DA 1983, Insect Pests of Field Crops, Department of Primary Industries & Fisheries, QI83013.
- Crop Insects: The Ute Guide. Northern Grain Belt Edition. 2000, QI00102.
- Weeds: The Ute Guide. Northern Grian Belt Edition. 2000, QI00002.
- Sunflower: The Ute Guide. 2006, QI06043.