All quiet on the western front

In a remarkable contrast to the pest ‘battle lines’ of 2014, a number of crop establishment pests appear to be more subdued in 2015. Why would this be?

 

The 2015 winter growing season has already experienced some notable pests in the crop establishment phase, particularly Bryobia mites and various weevil species. However, many other common pests appear to virtually absent or only present in local ‘hot spots’.

There are various possible reasons for this, but most likely:

i) In many regions of Victoria and southern NSW, the 2014 cropping season ended prematurely with a sustained dry period from late winter. This will have severely capped the development of pest populations and their over-summering eggs.

ii) Many of last year’s ‘big’ pest populations (aphids, caterpillars, mites and beetles), by virtue of their size, undoubtedly left ‘in their wake’ a greatly-enhanced community of beneficial natural enemies. Carabid and other predatory beetles, parasitic wasps, spiders and insect pathogens are among the bigger groups. These beneficials undoubtedly reduced the spring populations of pests (and their egg carry-over to autumn) and also helped to diminish the emerging autumn generations of 2015.

Aphids

In various parts of the Victorian Northern Country, inspections of numerous cereal crops revealed no or extremely low numbers of (mostly winged) cereal aphids. Further south in the Victorian Wimmera, cowpea aphids that were previously reported to be in high numbers in vetch (see Pest Facts Issue No. 2) were so diminished by late May they were very hard to find. Nearby in volunteer faba beans, many of the cowpea aphids had been parasitised.

Balaustium mites

Balaustium mites are a common and distinctive mite that attacks many establishing crops. They are regarded as an emerging crop pest in southern Australia with increasing reports to PestFacts over the last 5 years. In 2015, researchers and agronomists have reported that the pest is undetectable in the NSW Riverina, and Victoria’s North East, Northern Country and Western districts.

Slugs

The relatively early break in many areas was expected to give rise to a significant surge of grey field slug activity at crop emergence. In Victoria’s southwest, grey field slug populations have been patchy and much less active than in previous years. Researcher, Dr Michael Nash, has reported that slug numbers are much lower than in the last few years, with only a few growers needing to reapply baits.

In contrast, black keeled slugs appear to be at similar levels to last year. They were recorded in high numbers in the last weeks of May across stubble-retained paddocks north of Albury, in the NSW Riverina.

Lucerne flea and redlegged earth mite

In the NSW Riverina, the autumn break was early in 2015, but surprisingly pest problems have been patchy. Lucerne flea has not been causing the same level of threat to crops and pastures as in previous years, particularly last year. Redlegged earth mite have been slow to establish in parts of the Riverina, although they might still increase to become a serious pest for later establishing crops. There was one exception, areas of a canola crop 50 km north west of Albury was severely damaged by mites, despite a seed dressing, presumably because of the extreme numbers of mites.

In the Victorian Wimmera and southern Mallee, current mite problems have also been minimal, in part because of the late break. Many crops are still just emerging.

 

Source of field reports

Annabel Clouston – Researcher, cesar

Ben Cordes – Agronomist, Tylers Hardware & Rural Supplies (Victorian Wimmera)

Josh Douglas – Researcher, The University of Melbourne

Peter Emerson – Agronomist, Elders (NSW Riverina)

Alana Govender – Extension entomologist, cesar

Lincoln Harris – Agronomist, Elders (NSW Riverina)

Rob Harrod – Agronomist, Elders (Victorian North East)

Stuart McColl – Agronomist, Kagome (Victorian Northern Country)

Michael Nash – Entomologist, SARDI (Adelaide)

Greg Toomey – Agronomist, Landmark, (Victorian Northern Country)