Downs update – Symphyla and other soil pests

Fol­low­ing the recent detec­tion of sym­phy­la in some cot­ton fields on the Dar­ling Downs, DAFF Ento­mol­o­gy have been test­ing sam­pling strate­gies for this poten­tial pest of cot­ton.

Lit­er­a­ture for a sim­i­lar sym­phy­la species in North Amer­i­ca sug­gest­ed that bait­ing with pota­toes may be an effec­tive strat­e­gy for assess­ing sym­phy­la abun­dance and whether indi­vid­u­als were active­ly feed­ing or in a restive non-feed­ing devel­op­men­tal phase.

Black field earwig nymph (6 mm)

Black field ear­wig nymph (7 mm)

Wireworm larvae (20mm)

Wire­worm lar­vae (20 mm)

Dur­ing the last fort­night we have been assess­ing a range of veg­etable baits in a field where sym­phy­lans were recent­ly found using soil sam­pling. So far none of the dif­fer­ent baits test­ed (pota­toes, pump­kin, pineap­ple, rock­mel­on etc) have been found to attract sym­phy­la, how­ev­er these baits have high­light­ed that the field is also host to very high num­bers of black field ear­wigs and wire­worm.

This might sug­gest that some of the dam­age that has been observed may be due to a com­plex of soil pests that remain large­ly unde­tect­ed with­out bait sam­pling.

Many peo­ple have report­ed poor crop estab­lish­ment in fields where only very low num­bers of soil pests have been found with stan­dard soil sam­pling. The large num­bers of soil pests encoun­tered on the baits demon­strates the need to use mul­ti­ple sam­pling meth­ods to deter­mine the abun­dance of soil pests.

Soaked grain baits are rec­om­mend­ed for sam­pling soil pests (see below). Soil pests are attract­ed to eth­yl­ene cues emit­ted by ger­mi­nat­ing grains. For fields that have had poor lev­els of crop estab­lish­ment it may be worth bait­ing for these soil pests to help bet­ter deter­mine the cause of what has been a per­plex­ing start to the 2013/14 sea­son for some cot­ton grow­ers.

Germinating seed bait technique

Fol­low­ing plant­i­ng rain or irri­ga­tion:

  1. Soak insec­ti­cide-free crop seed in water for at least two hours to ini­ti­ate ger­mi­na­tion.
  2. 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.
  3. Mark the posi­tion of the seed baits as high pop­u­la­tions of soil insects can com­plete­ly destroy the baits.
  4. One day after seedling emer­gence, dig up the plants and count the insects.

Tri­als have shown that the type of seed used makes no notice­able dif­fer­ence 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.