Management of the soil pest complex: millipedes, springtails and symphylids
Rarely occurring as a single species, the soil pest complex can attack sugar beet from germination onwards, causing feeding damage to the roots and stem below the soil. Symphylids may also attack crops such as potatoes, tomatoes and lettuce.
Risk factors in field crops
- The risk is higher in cold, wet springs
- The complex is more common in fields with plenty of fresh organic matter or an open soil texture
- Plants are less susceptible to attack by millipedes once they are beyond the four true leaf stage
Soil pest complex life cycle, identification and crop damage
Millipedes (Blaniulus spp., Brachydesmus spp., Polydesmus spp. and others) occur in two types: snake millipedes and flat millipedes. All have a body with many segments. Each segment has two pairs of legs. They are approximately 1 mm in diameter and 10–20 mm long.
Adults breed in spring and summer, laying eggs in ‘nests’ in the soil. The young have three pairs of legs and add more segments, each with a pair of legs, until they mature after 2–3 years.
Subterranean springtails (Onychiurus armatus and Folsomia fimetaria) are white with an elongated body (on average 1 mm in length). Springtails have two breeding peaks per year: one in late spring and the second in the autumn/winter.
Scientific name: Sminthurus spp. and Bourletiella spp.
In contrast to the subterranean springtails of the soil pest complex, these springtails live above ground. They have a globular body and are light green or purplish.
They feed on cell contents through puncture wounds on the cotyledons or true leaves, causing superficial damage. They are not a serious pest.
On the leaf, however, green-coloured springtails can easily be mistaken for green aphids. They are readily distinguished from aphids because they jump when disturbed.
Symphylid (Scutigerella immaculata) adults are active, with a slender body that is 5–7 mm in length. They are white and shiny, with two long antennae and 12 pairs of legs.
Adults lay eggs throughout the year in batches of up to 20. Young symphylids have three pairs of legs and go through a series of moults, adding a pair of legs each time until they have 12 pairs in total. This process takes 3 months and symphylids can live for several years.
Some feeding damage is superficial, but some can be deeper, causing pits in the roots, especially before emergence. Grazing of the root stem and root hairs causes the seedling to collapse and die. Sites at which damage has occurred can be prone to secondary pathogenic fungi.
Non-chemical and chemical control
Damage is more severe when seedling growth is slow. Measures to improve establishment can help plants grow away from damage.
Bare patches in the field may suggest damage by the soil pest complex. Millipedes and symphylids may be seen in soil samples with the naked eye, but magnification is needed to see springtails.
There are no thresholds. Yield loss is associated with loss of plants. Crops with very low populations may need to be re-drilled with insecticide-treated seed.