PestFacts 4 September 2023

Pea weevil monitoring and spraying

In response to recent warm weather, the SARDI pea weevil model predicts adult pea weevil (Bruchus pisorum) began their invasion of pea crops in most South Australian regions on the 25 August.

How to monitor

Sweep-net monitor at 5 to 7 day intervals around the edge of pea crops, about 2 metres into the crop. Concentrate on areas near trees and other hibernation sites such as sheds. Check the net every 25 sweeps. The spray threshold is at least 2 adults per 25 sweeps, averaged over 5 to 10 sampling sites.

To effectively control pea weevil, adults must be killed before they lay eggs. This means spray timing is essential to achieve good pea weevil control.

We estimate that 75% or more of the weevil population is likely to have emerged and moved into crops by 25 August, with egg-laying to start around 8 September. This egg laying estimate is based on the:

• predicted arrival date of 25 August
• predicted maximum temperatures in the coming days.

If the spray threshold is reached, spray podding pea crops around 8 September. For later crops, where pods won't form until after this date, spray as the first flowers wither.

Border spraying

If thresholds are exceeded, a 20 to 40 metre wide border spray is the most cost-effective way to control pea weevil, as adults will invade from the border.

However, if sweep-net monitoring reveals densities of native budworm (Helicoverpa punctigera) exceeding the threshold, then one whole-crop spray will control both pests.

After pea weevil treatment, monitoring and threshold-based treatment for native budworm should continue as normal.

Early harvest

Good pea weevil management includes harvesting pea crops as early as seasonal conditions permit.

Early harvesting ensures that the pea weevil infestation remains immature with no adults present to disperse during harvest. This minimises pod and seed shatter, damage from pea weevil feeding, and the risk of grain rejection at delivery.

Treating early provides long-term benefits and helps reduce the abundance of pea weevil in the same location next year.

Using SARDI's Etiella model

SARDI's degree-day Etiella model predicts the timing of initial spring lucerne seed web moth or Etiella flight activity using local daily maximum and minimum temperatures from 21 June onwards. The model is available online at SARDI Etiella degree-day model (etiellamodel.app).

Crop monitoring should begin before the cumulative total of degree-days (base 10°C) first reaches 351 (about 10% into peak flights). Ideally, start monitoring 1 to 2 weeks earlier than this figure (around 300). As a guide, daily maximum temperatures of 25°C would see cumulative degree-days increase from 300 to 351 in about 7 days.

The date when the model reaches 351 degree-day accumulations corresponds to the predicted date of 10% onset of peak moth flight activity. We recommend starting in-crop monitoring of lentil crops around 7 to 10 days earlier than this date, at around 300 degree day accumulations.

Current model predictions for degree-day accumulations (to 30 August) in many regions are still below 300 degree days:

• Roseworthy – 212
• Cummins – 214
• Cleve – 212
• Port Pirie – 190
• Keith – 182
• Horsham (Vic) – 147

Monitoring for Etiella moths

To monitor, use a sweep net and take samples of 20 sweeps in at least 5 locations. If moth numbers exceed threshold guidelines of 1 to 2 moths per 20 sweeps, consider immediate treatment with a registered insecticide. Begin monitoring again 7 to 10 days after treatment.

Etiella moths:

• are 10 to15 millimetres long
• are greyish-brown in colour with a pale white stripe running along the front edge of the forewings
• have a prominent 'beak' protruding forward from the head
• lay eggs on the calyx – eggs are clear in colour and change to orange prior to hatching.

If you have any feedback on the online Etiella model, please contact:

Kym Perry
Phone: 0421 788 357
Email: kym.perry@sa.gov.au

Time to start considering TimeRite

Redlegged earth mite (RLEM, Halotydeus destructor) is a common resident pest. RLEM are active from autumn to late spring and have up to three generations per year. The final or third generation produces over-summering eggs that will hatch the following autumn.

Controlling RLEM before the over-summering eggs are laid is an effective way of reducing populations for next autumn. You can use the TimeRite calculator to find the optimal spray dates during spring for your property.

However, as RLEM is becoming increasingly resistant to many pesticides, it is important to only spray if your risk is high.

How to determine your risk

To help you decide if a TimeRite application is beneficial, use the Grains Research and Development Corporation's (GRDC) Redlegged earth mite best management practice guide to evaluate the risk of RLEM on your property based on:

• previous crops
• observation of mites in spring
• sensitivity of the future crops.

Alternatively, you can use the interactive RLEM severity risk assessment developed by Cesar Australia.

Ensure that you correctly identify the mites you find as the TimeRite strategy only works on RLEM.

Identifying RLEM

RLEM are up to 1 millimetre in length, with globular-shaped black bodies and red legs. The three other main crop mites look similar, but have some small differences. The GRDC Crop Mites Back Pocket Guide is a useful tool to help distinguish between these mites, and as a PestFacts SA subscriber you can always send photos and specimens to us.

RLEM often are found feeding in groups of up to 30 individuals, unlike other mite species.

For more information, see Resistance management strategy for the Redlegged Earth Mite in Australian grains and pastures.

Using the Russian wheat aphid threshold calculator

If you are seeing Russian wheat aphid (RWA, Diuraphis noxia) use the RWA action threshold calculator to help decide your next steps. The calculator helps decide if spraying is economically justified by considering the following factors:

• cost of control
• cereal market price
• aphid numbers.

When using the calculator, monitoring at growth stage 30 (GS30) stem elongation is recommended. Plants at these earlier growth stages will often be able to compensate, just as they can compensate for grazing or herbicide damage. Economic justification for sprays before GS30 cannot be calculated with available data. For more information on using the calculator, see How to use the new Russian wheat aphid action threshold calculator.

How to monitor for RWA

1. At GS30 count the number of tillers in 50 centimetre row lengths, choosing at least 5 areas of the paddock (For example, you may have 433 tillers counted).
2. In the same row lengths count the number of tillers with symptoms such as leaf rolls sheltering aphids inside, whitish, yellowish to pink-purple chlorotic streaks along the length of leaves or stunted plants with flattened tillers. Continuing this example, if there are 43 tillers with symptoms, you have 10% (0.1) tillers with symptoms (43/433).
3. In or around each of the five areas, check 20 tillers (100 in total) with symptoms for the presence of RWA. If there are 54 tillers with symptoms and RWA, then at this stage you have 54% (0.54) tillers with symptoms that also have RWA.
4. Multiply the percentage of tillers with symptoms with the percentage of symptomatic tillers that are hosting RWA. This will result in the percentage of tillers with RWA. In this example, 0.1 × 0.54 = 0.054, meaning 5.4% of tillers with RWA

Cowpea aphid spotted in legumes

Reports of cowpea aphid (Aphis craccivora) have increased over the past few weeks. It was reported in vetch at Hornsdale, and in lentils at Paskeville. It has previously been reported in lupins, as covered in PestFacts 14 August 2023.

While cowpea aphid involvement hasn't been confirmed, they have historically been implicated in photosensitisation of livestock grazing on infested plants, and a precautionary approach may be wise. If you are concerned about photosensitisation of livestock feeding on crops and pastures infested with cowpea aphid, seek veterinary assistance for correct diagnosis and management of the condition.

Identifying cowpea aphid

Adult cowpea aphids are shiny black in colour and nymphs are dull grey as they are lightly dusted with wax. All stages have white and black legs. Cowpea aphid can reach up to 2 millimetres in length.

Cowpea aphids tend to colonise single plants before moving onto surrounding plants to create 'hot spots' within a crop. They typically colonise legumes including lucerne, vetch, medic, lentils and faba beans. Other aphids which commonly also colonise these hosts in SA include blue green aphid and pea aphid. Both these aphids are larger and pale green so are unlikely to be confused with cowpea aphid.

Cowpea aphid management

Consider natural enemies being before spraying as many are very effective in suppressing aphid populations. When monitoring, keep an eye out for aphid mummies (parasitoid wasps), hoverfly larvae, lacewings and ladybeetles.

If chemical control is warranted, check the Australian Pesticides and Veterinary Medicines Authority's Public Chemical Registration Information System Search for chemical options. Spot spraying may be sufficient. Try to avoid the use of broad-spectrum insurance sprays and apply insecticides only after monitoring and distinguishing between aphid species. You can use the Beneficials chemical toxicity table to help consider options to preserve beneficials in crop.

Field day showcases latest research

Want a chance to discuss current SARDI research with the program leaders and researchers? Many will be attending the Minnipa Agricultural Centre Field Day on 13 September.

The annual field day showcases the extensive trials and research being undertaken for low rainfall farming on upper Eyre Peninsula.

Register now.