Check for establishment pests before planting summer crops

Crops are most sus­cep­ti­ble to pest dam­age at the seedling stage. Pests feed­ing on seedlings can reduce plant estab­lish­ment, increase weed com­pe­ti­tion, delay flow­er­ing and low­er yields. In some cas­es there may be a need for re-sow­ing.

Most of the estab­lish­ment pests found in the north­ern region are soil-dwelling insects. Soil insects may be dif­fi­cult to detect pri­or to sow­ing. The key prin­ci­ples that under­pin man­age­ment strate­gies for estab­lish­ment pests include pest iden­ti­fi­ca­tion and mon­i­tor­ing. Knowl­edge of pad­dock his­to­ries also ben­e­fits deci­sion mak­ing for estab­lish­ment pests. This is espe­cial­ly the case for res­i­dent pests but more dif­fi­cult for tran­sient pests that are more mobile and move greater dis­tances.

Early pest damage can impact on final yield

Ear­ly pest dam­age can impact on final yield

Farm man­age­ment and dif­fer­ent cul­ti­va­tion prac­tices can influ­ence the type and num­ber of estab­lish­ment pests. For exam­ple;

  • Weedy fal­lows and vol­un­teer crops encour­age soil insect build-up
  • Insect num­bers decline dur­ing a clean long fal­low due to lack of food
  • 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.
  • Crops after pas­ture can have high lev­els of scarab lar­vae
  • Zero tillage encour­ages ben­e­fi­cial preda­to­ry insects and earth­worms but also some estab­lish­ment pests.
  • 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 pri­or to, or at, sow­ing. Since dif­fer­ent insects require dif­fer­ent con­trol mea­sures, the species of soil insects pos­ing a threat to the crop must be iden­ti­fied before plant­i­ng.

Mon­i­tor for soil insects

Soil sam­pling

This involves tak­ing ran­dom spade sam­ples across the field. Ensure spade sam­ples are deep enough to take in the moist soil lay­er as many soil insects inhab­it this inter­face between dry and moist soil. Hand-sort sam­ples to deter­mine the type and num­ber of insects. Spade sam­pling can be done for all soil-dwelling pests how­ev­er it is labo­ri­ous, time con­sum­ing and dif­fi­cult in wet soils.

Ger­mi­nat­ing seed baits

Seed baits can be used to mon­i­tor for the pres­ence of wire­worms, ear­wigs and wing­less cock­roach­es.

  • Soak insec­ti­cide-free crop seed in water for at least two hours (or overnight) to ini­ti­ate ger­mi­na­tion. Use the type of seed to be sown e.g. if plant­i­ng sorghum, use sorghum seed for the baits.
  • Bury a dessert spoon 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.
  • Place baits at the inter­face of the moist sub­sur­face soil. In very dry soil, water the baits to ensure ger­mi­na­tion. The insects are attract­ed to the ger­mi­nat­ing seed, not the seed itself.
  • Don’t for­get to mark the posi­tion of the baits.
  • Five days after plac­ing the baits, dig up the ger­mi­nat­ing seed and count the insects.

Although mon­i­tor­ing for soil insects may seem time con­sum­ing, not know­ing the poten­tial risk may be more cost­ly in the end if re-sow­ing is required.

Watch a ‘how to’ video on the prepa­ra­tion and use of ger­mi­nat­ing seed baits.

False wireworm larvae and adult

False wire­worm lar­vae and adult

Cutworms

Cut­worms

Man­ag­ing soil insects

Cul­tur­al con­trol

Crop residues and weedy fal­lows favour sur­vival of soil insects.

Cul­ti­va­tion can reduce some soil dwelling insects by expos­ing them to adverse envi­ron­men­tal con­di­tions, thus pre­vent­ing pop­u­la­tion increas­es.

Use high­er seed­ing rates to com­pen­sate for seedling loss­es expect­ed.

The use of press wheels at sow­ing increas­es com­paction of soil around the seed to enhance ger­mi­na­tion and can also reduce move­ment of pests in the soil.

Chem­i­cal con­trol

Insec­ti­cides may be applied to soil or seed at sow­ing. Seed treat­ments can pro­tect the seed and seedling from low to mod­er­ate attack by insects dur­ing emer­gence and estab­lish­ment. Seed treat­ments that con­tain imi­da­clo­prid, fipronil and thi­amethx­am pro­vide some pro­tec­tion from var­i­ous soil dwelling pests. Please note that cut­worms are not con­trolled by seed applied chem­istry.

The use of soil-incor­po­rat­ed insec­ti­cides can have a sig­nif­i­cant impact on oth­er insects in the soil includ­ing ben­e­fi­cials. Grain baits con­tain­ing insec­ti­cide applied at sow­ing offer good pro­tec­tion from black field ear­wigs and false wire­worm adults.

If dam­age occurs after sow­ing, no treat­ment is avail­able, oth­er than re-sow­ing bare patch­es with an insec­ti­cide treat­ment. Sow­ing sum­mer crops in fields with very high pop­u­la­tions of soil insects should be avoid­ed.

For more infor­ma­tion about estab­lish­ment pests and avail­able thresh­olds vis­it: http://ipmguidelinesforgrains.com.au and ‘how to recog­nise and mon­i­tor soil insects’ on the DAFF web­site.