Update on other crop pests

Cutworm activity appears to be on the decline, but other caterpillars attacking cereals and pasture crops are becoming more evident. Yellowheaded cockchafers, weevils and blue oat mite have been damaging cereals

 

Cutworms

Reports of cutworms (Agrotis spp.) damaging crops have abated, but there are still some cases of paddocks incurring seedling loss. A relatively unusual incident of seedling chickpeas (4-leaf) being damaged by cutworms was reported near Elmore in Victoria’s Northern Country. Densities of 5-40 per square metre were cutting off seedlings at the ground level; some larvae were in shallow burrows, perhaps suggesting the process of pupation in which larval feeding stops. Alpha-cypermethrin provided effective and rapid control. In Victoria’s Wimmera, near Whycheproof, canola crops have recently suffered some seedling loss from relatively low numbers of cutworms. Chlorpyrifos had previously been applied to this paddock. We do not expect the incidence of damaging populations of cutworms to extend into August. Refer to PestFacts Issue No. 3 and PestFacts Issue No. 4 for further information on cutworms.

 

Caterpillars in cereals

Moderately damaging populations of caterpillars have been recorded in several late barley crops east of Bordertown in Victoria’s Wimmera. Most of the crop (2-4 leaf) has experienced foliar damage by both climbing and ground-active caterpillars (Proteuxoa spp). This native caterpillar pest may be related to the white tailed black cutworm which was found in high numbers last winter in South Australia’s Central and Western Eyre Peninsula. They are cereal and grass feeding caterpillars distantly related to armyworm and common cutworm.

Mature stage armyworms (probably Leucania convecta) have been identified attacking a pasture seed crop near Dubbo in the NSW Central West Slopes & Plains. Like cutworms, armyworms at this stage of development will be reasonably voracious, but are likely to cease feeding and pupate within the next month. Egg-laying for the ‘spring feeding’ generation of armyworms generally commences in August-September. Cereal crops (particularly barley) should be monitored from spring onwards. Armyworm larvae are most active at night.

 

Yellowheaded cockchafers

In the Narrandera region of the NSW Riverina, two barley crops were seriously damaged by high densities (20-30 larvae per square metre) of yellowheaded cockchafers. Both paddocks have needed to be reworked, treated and replanted.

Yellowheaded cockchafer (Sericesthis spp.) grubs are “C” shaped, creamy-grey in colour and have a yellow head capsule. When fully grown in winter they are about 25-30 mm long. The grubs live in the soil until mid-to-late summer, where they emerge as yellow-reddish beetles about 10-15 mm in length. Like redheaded pasture cockchafers, yellowheaded cockchafers are primarily root feeders and do not come to the surface to feed. They mostly attack cereals, but will also cause economic damage to pastures.

Control of yellowheaded cockchafers is complicated. Insecticides are largely ineffective because the larvae never come to the surface to feed. Re-sowing bare areas using a higher seeding rate is often the most effective strategy. Cultivating the affected areas prior to sowing a crop will help reduce pest populations as it exposes the grubs to predation by predatory invertebrates and insectivorous birds.

To check paddocks for cockchafers, dig in the affected areas. Crops sown into long term pasture paddocks are most vulnerable to attack. Be aware that if you did not have problems with cockchafers last year, it does not mean that you won’t have this year. Adult beetles achieve long distance dispersal by flying, usually at dusk on warm evenings in late spring-early summer.

 

Weevils

Several weevil species that attack crops will now be active. Correct identification is important, but quite challenging. An unknown species of weevil larvae has caused damage to large patches in paddocks of barley and wheat in the GreenLake area of the Victorian Wimmera. The paddocks had been previously under lucerne for 10+ years. The 5-10 mm cream coloured larvae are chewing the underground shoot or stem, causing wilting and yellowing.

The GRDC Back Pocket Guide - Crop Weevils provides an excellent resource on the main species of weevils in cropping. More information on weevils can also be found in PestFacts Issue No. 3 or by clicking here.

 

Blue Oat Mites

Blue oat mites (Penthaleus spp.) have been holding back seedlings in an oat crop near Ballarat in Victoria’s Central District, and in an establishing pasture on the NSW Tablelands. Blue oat mites attack a variety of crops and pastures, including cereals, oilseeds, legumes and fodder crops. They can also survive on a variety of weeds, particularly broad-leaved weeds.

There are several options to control blue oat mites. If using foliar insecticides, these should be applied within three weeks of the first appearance of mites. This will allow for further hatching of blue oat mites from over-summering eggs but will be before mites reach the adult stage and begin to lay winter eggs. It is important to distinguish blue oat mites from other mite species, such as redlegged earth mites and Bryobia mites, as this will influence control. Click here for images of blue oat mites and refer to PestFacts Issue No. 4 for further information.

 

* Sources of field reports

Mick Duncan – Agronomist, Northern Agriculture (NSW Northern Tablelands)

Erin Johns – Agronomist, JSA Independent (Victorian Wimmera)

Pat Hernon – Grower (Victorian Wimmera)

Rob Launder – Consultant, AgriTech Rural (Victorian Wimmera)

Adam Pearce - Agronomist, Clovercrest Consulting (Victorian Wimmera)

David Ryan - Agronomist, Independent Agronomy Services (Victorian Central District)

David Sergeant – Agronomist, Elders (NSW Riverina)

Glen Shepherd – Agronomist, IMAG Consulting (NSW Central West Slopes)

Greg Toomey – Agronomist, Landmark (Victorian Northern Country)