Symphyla

Symphyla (Hanseniella spp.) generally feed on decomposing organic matter. Occasionally they can cause problems with crop establishment, although most establishment issues where symphyla are present are caused by a combination of soil pest species rather than symphyla alone.

Symphyla are fast moving, up to about 10mm long with 12 pairs of legs. The nymphs look similar to adults, but have fewer legs. They care easily confused with other small soil-dwelling arthropods such as diplura or collembola.

A symphylan (left) is very similar in appearance to a dipluran (right)

Widespread and present in most soil types, with a preference for loose or cracking loams, and soils high in organic matter. They can attack roots of a wide range of plant species, but the damage is most noticeable in tap-rooted crops such as cotton. Symphyla are also considered pests of sugarcane.

Damage

Root system development can be stunted. If severe, the tap root may stop growing and the subsequent root branching is often referred to as ‘witches’ broom’.

Affected plants exhibit wilting symptoms (even in good soil moisture), general stunting, and sometimes seedling death. Symptoms are more prevalent if plants are stressed and cannot grow additional roots fast enough to offset the damage.

Typically symphyla feed on roots where the soil is moist. As the moisture profile dries out, the continuous root pruning can leave plants stranded in the top 10-15cm of soil.

Monitoring and thresholds

Symphyla are delicate—avoid compacting the soil while sampling.

  • Insert a shovel to full depth at the plant line and carefully lever the soil out for closer inspection.
  • Start examining soil from the bottom of the shovel, as symphyla are more common in the deeper, wetter part of the soil profile.
  • Holding a soil clod in one hand, use your other hand to carefully break the soil apart while keeping a close eye on the inner surfaces for movement (they will rapidly shift to avoid sunlight).

Control

It is difficult to target symphyla with insecticide as they can be active to depths of up to 1m, and insecticide at planting may not provide sufficient protection if roots quickly grow past the treated zone.

Ensure that susceptible fields are planted last so that the warmer conditions aid rapid establishment. Monitor plant health closely, and if establishing plants show signs of moisture stress (and symphyla are present) a quick irrigation will aid plant development and allow the crop to out-grow the pest.

If more than 5 symphyla are found per shovel full of soil and establishment is poor enough to warrant replanting, consider a fibrous-rooted alternative crop such as maize or sorghum, or replant cotton in another field if possible.

Further information