Weevils, slaters and Bryobia

Despite more reports of Bryobia mite, the impact of this pest should soon diminish. However, weevil and slater damage may persist well into winter

 

Weevils

Various weevil species continue to cause problems to seedling and establishing crops, particularly in southern NSW and northern Victoria. In each case, it seems to be the adult weevils inflicting the damage. Weevils have wiped out 40 ha of a canola crop (4-6 leaf stage) north west of Albury in the NSW Riverina. The pace of crop loss was dramatic, and occurred over only a few days. It appears this damage was caused by Mandalotus weevils, which ate out entire plants and/or ring-barked others. The affected area will need to be re-sown.

Weevils have caused patchy leaf damage and lopping in a barley crop near Murrayville in the Victorian Mallee. Identification has proved difficult but the weevils appear to be spinetailed weevil, spotted vegetable weevil or Mandalotus weevil. As the crop is advancing well, treatment is unlikely to be warranted. Spinetailed weevils also appear to have ring-barked canola seedlings in the Elmore area of the Victoria’s Northern Country, although the crop does not appear to be under substantial threat.

For assistance in distinguishing weevils see PestFacts Issue No. 2 or the GRDC Weevil Back Pocket Guide.

Typically, adult weevils emerge in late spring through to autumn, and lay eggs with, and immediately after, the autumn break. The presence of adults almost certainly means there is, or soon will be, a new generation of larvae. In many cases, crops will out grow the damage caused by larvae, which generally feed on the developing roots of crops, but monitoring weak areas of paddocks is recommended. Unfortunately, in most cases, chemicals are not effective against larvae, except those that feed above the soil surface (e.g. vegetable weevil).

Slaters

Slaters continue to be a problem for canola crops in a number of areas of the NSW Riverina. In several crops located north and south of Lockhart, slaters have been very disruptive in canola crops (2-4 leaf) sown into paddocks with plenty of organic matter (brown vetch mulches on top of 2013 wheat stubbles). Plants were sporadically missing or ring-barked along most rows, with numerous slaters present at the base of weakened plants early in the morning. In one paddock, a mixed formulation insecticide seed dressing provided partial control, but large numbers appeared to overwhelm the product. We have also received reports of slaters in canola north of Yarrawonga and further issues being observed in canola near Temora, in the NSW Central West Slopes & Plains district.

For detailed information on slaters, including their occurrence, lifecycle, behaviour, damage symptoms and management strategies, go to the new PestNote on slaters or see PestFacts Issue No. 2.

Bryobia mites

Bryobia mites have been prevalent in many areas this season. Further to reports in PestFacts Issue No. 1 and PestFacts Issue No. 2, Bryobia mites have been responsible for holding back 2nd leaf canola crops at separate locations north and south of Lockhart, in the southern Riverina of NSW. The mites were successfully controlled with omethoate. Bryobia mites were also present in patches of a barley crop near Echuca and in a canola crop near Shepparton both in Victoria’s Northern Country.

It is important to distinguish Bryobia mites (Bryobia spp.) from other mite species before deciding on control options. Established crops can tolerate moderate infestations of Bryobia mites and numbers will naturally decline in most areas with the onset of cooler winter conditions. For more detailed information on Bryobia mites, including their occurrence, lifecycle, behaviour, damage symptoms and management strategies, go to the new PestNote on Bryobia mites.

 

Source of field reports

Annabel Clouston – Researcher, cesar

Alan Edis – Agronomist, Landmark (NSW Central West Slopes & Plains)

David Eksteen – Consultant, Agricultural Consulting (NSW Riverina)

Heidi Gooden – Agronomist, Delta Ag (NSW Riverina)

Lincoln Harris – Agronomist, Elders (NSW Riverina)

Greg Toomey – Agronomist, Landmark (Victorian Northern Country)

Matthew Whitney – Agronomist, Dodgshun Medlin (Victorian Mallee)