Soil and establishment pests

A number of species of soil-dwelling arthropods can seriously reduce plant establishment and populations, and subsequent yield potential. Common pests include cockroaches, crickets, earwigs, scarabs, symphyla and wireworms. Often more than one species is present.

See the ‘Best Bet’ IPM strategies for establishment pests in northern and southern growing regions,
developed as part of the Decision making for insects in grain crops project. 

Examples of the more common insect pests at crop establishment are:

Pest Description Damage
Black earwigs
Nala lividipes		 Up to 15mm long, shiny black with a flattened body and a pair of curved pincers at the end of the body.

Nymphs resemble adults but are wingless and the pincers are paler.

 Eat newly sown and germinating seed and crop roots, causing poor establishment. Feeding on secondary roots may cause lodging. Can also feed on decaying plant matter.
Black field crickets
Teleogryllus commodus		 Adults are black or brown and up to 30mm long with large hindlegs modified for jumping.

Nymphs are similar in shape but are smaller, paler and wingless.

 Feed on leaves, stems and pods. Seedlings may need replanting.

Can feed on the back of sunflower heads and maturing seeds.

Common in cracking soils
Scarabs
(several species)		 Larvae grow to about 25-30mm long, with creamy-white bodies and light to dark-brown heads. They curl into a C-shape when disturbed. Some larvae have a greyish tinge at the rear end.

Adults are oval-shaped, up to about 17mm long, and brown to black.

 The soil-dwelling larvae feed on roots and underground stems. Plants that do not die tend to be more prone to lodging.
Symphyla
Hanseniella spp		 Fast moving, up to about 10mm long with 12 pairs of legs.

Nymphs look similar to adults, but have fewer legs.

 Occasional establishment pests that attack roots of a wide range of plant species, causing wilting or plant death.
Wingless cockroaches
Calolampra spp.		 Up to 35mm long, shiny brown with pale margins. Some adults may be winged.

Nymphs are initially greyish-brown or tan.

 Feeds on cotyledons, leaves and growing points. May sever the stem of small seedlings.
Wireworms
(several species)		 Long thin cream to yellow or tan larvae up to 35mm long.

True wireworms are soft-bodied, and flatter in cross-section with a flattened head. False wireworms are hard-bodied, cylindrical and segmented with a rounded head.

 Soil dwelling larvae feed on germinating seed and chew on seedling roots and shoots, resulting in patchy stands (reduced vigour or seedling death).

False wireworm adults can chew on seedlings at or above ground level, ring-barking or completely cutting the stem.

Many soil and establishment pests live below ground or are nocturnal, making them hard to find, and most have relatively few natural enemies.

Note that other soil fauna (that don’t damage crops in northern regions) may also be present in soil samples:

  • centipedes—long, many-segmented animals with legs all along the body. They have long feelers and tail appendages, and can move very quickly
  • millipedes—long, cylindrical, segmented body with an extremely high number of legs. They have short feelers, no tail appendages and move more slowly than centipedes. When disturbed, they coil up into a spiral
  • isopods (woodlice or slaters)—small grey animals up to 7–10mm long with long feelers and 8 pairs of legs. They are usually found in groups under trash and in cracks in the soil
  • earthworms—true soil animals, unlike centipedes, millipedes and isopods, which live on or near the soil surface. Earthworms are valuable in improving soil texture
  • ants—live in colonies which are mostly underground. The wingless workers gather food, particularly pasture seeds when available, for the colony.

Soil pest presence varies with soil-type, season, crop rotations, and other management practices such as cultivation, and control thresholds are usually different for summer and winter crops.

Weedy fallows and volunteer crops encourage soil insect build-up. Insect numbers decline during a clean, long fallow due to lack of food. Summer cereals followed by volunteer winter crops promote the build-up of earwigs and crickets.

High stubble levels on the soil surface can increase numbers of some soil insects (food source) but can also mean that pests continue feeding on the stubble instead of on germinating crops. False wireworms are found under all cultivation intensities but decline if stubble levels are very low. Incorporating stubble promotes black field earwig populations.

Zero tillage encourages beneficial predatory insects and earthworms.

Listen to the sound of a black field cricket.

Monitoring

Normally, apply soil insect control measures at sowing. Since different insects require different control measures, you must identify any species present before planting.

Soil insects are often difficult to detect as they hide under trash or in the soil. Immature insects such as false wireworm larvae are usually found at the moist/dry soil interface.

Spade sampling

Dig up a spade-full of soil at random locations across the field, ensuring samples are deep enough to include the moist soil layer. Hand sort through the soil to determine type and number of soil insects.

Spade sampling is most useful for insects such as scarab larvae or symphyla, but is laborious, time consuming and difficult in heavy clay or wet soils.

Baiting

Pests such as wireworm can be detected with baiting, either with germinating seed or other food sources attractive to soil pests (e.g. potatoes or flour). Place baits immediately after planting rain, and position as shown in the diagram below.

If using the germinating grain technique:

  1. Soak insecticide-free crop seed in water for at least 2 hours to initiate germination. If available, use seed of the same crop type you plan to plant in the field.
  2. Bury a dessertspoon full of soaked seed under 1cm of soil at each corner of a 5×5 metre square at 5 widely spaced sites per 100ha.
  3. Mark the position of the seed baits as high populations of soil insects can completely destroy the baits.
  4. 1 day after seedling emergence, completely dig up the baits and count the insects nearby.

Using germinating baits allows you to more easily find the baits once germinated (unless they are eaten) compared to buried material; however the delay between placing and assessing the seed can be a major disadvantage.

Suggested spacing and sampling pattern for baiting

Soil pests are difficult to study, and very few widely-agreed upon thresholds are available. DAF are currently researching soil insects, and will be considering thresholds as part of the project.

Management

In most cases, very few options are available when soil pests are detected post-plant. The best management approaches are to sample early and/or be aware of field histories and conditions that might be conducive to high populations. Maintaining good farm hygiene and considering pest preferences when managing stubble can help reduce populations. Crop rotations with tolerant species or re-considering planting windows may also help.

In irrigated crops where roots have been damaged, manage irrigation (e.g. decrease irrigation intervals) to minimise moisture stress while plants recover.

Baiting with insecticide treated grains at sowing, using seed treatments or insecticides in the furrow at sowing may be options in some circumstances. Always check product registrations.

Further information