Soil-dwelling insect pests can seriously reduce plant establishment and populations, and subsequent yield potential.
Soil insects include:
Different soil insects occur under different cultivation systems and farm management can directly influence the type and number of these pests.
- 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 promote some soil insects due to a food source but this can also mean that pests continue feeding on the stubble instead of germinating crops.
- Zero tillage encourages beneficial predatory insects and earthworms.
- Incorporating stubble promotes black field earwig populations.
- False wireworms are found under all intensities of cultivation but decline if stubble levels are very low.
Soil insect control measures are normally applied at sowing. Since different insects require different control measures, the species of soil insects must be identified before planting.
Soil sampling by spade
- Take a number of spade samples from random locations across the field.
- Check that all spade samples are deep enough to take in the moist soil layer (this is essential).
- Hand sort samples to determine type and number of soil insects.
Spade sampling is laborious, time consuming and difficult in heavy clay or wet soils.
Germinating seed bait technique
Immediately following planting rain:
- Soak insecticide-free crop seed in water for at least two hours to initiate germination.
- Bury a dessertspoon full of the seed under 1 cm of soil at each corner of a 5x5 m square at five widely spaced sites per 100 ha.
- Mark the position of the seed baits as high populations of soil insects can completely destroy the baits.
- One day after seedling emergence, dig up the plants and count the insects.
Trials have shown that there is no difference in the type of seed used when it comes to attracting soil-dwelling insects. However, using the type of seed to be sown as a crop is likely to indicate the species of pests which could damage that crop.
The major disadvantage of the germinating grain bait method is the delay between the seed placement and assessment.
Recognising soil insects
Detecting soil-dwelling insects
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.
- Huf S and Agnew J, 1994. Rain to grain. Queensland Department of Primary Industries, Information Series QI94039.
- Elder RJ, Brough EJ and Beavis CHS. Managing insects and mites in field crops, forage crops and pastures. Queensland Department of Primary Industries, Information Series QI92004.