Darling Downs grain growers have been placed on alert for bands of dayfeeding armyworms that are on the march, defoliating sorghum, corn and millet crops and threatening yield potential.
While reports suggest that the damage has been patchy so far, the Grains Research and Development Corporation (GRDC) warns that any outbreaks have the potential to cause significant yield loss if crops are defoliated before reaching physiological maturity.
At this time of year, high numbers of common armyworm and dayfeeding armyworm can defoliate seedling crops, summer crops that are still green as well as pasture.
The common armyworm is the same species of armyworm that causes damage to winter cereals in spring and Department of Agriculture, Fisheries and Forestry (DAFF) Principal Entomologist Dr Melina Miles believes that the high numbers now may be a carryover from the outbreak in northern NSW last spring.
“Armyworm outbreaks like these tend to last only one to two generations as disease, predation and parasitism have an impact on survival,” Dr Miles said.
“The threat to winter crops is expected to be low, but monitoring as the crops emerge, particularly in proximity to armyworm outbreaks now, is recommended.
“Both the common and dayfeeding armyworm larvae look similar to Helicoverpa larvae. Correct identification is important because armyworm cannot be controlled with Nuclear Polyhedrosis Virus (NPV), and helicoverpa have resistance to synthetic pyrethroids - the two most commonly used control options for these species.”
Dr Miles said control of dayfeeding armyworm in crops required good coverage to ensure contact with caterpillars, particularly in crops with thick canopies.
“If treating pastures beware of the long withholding periods for cattle grazed on this pasture with reference to export slaughter intervals and export grazing intervals. These intervals are not always marked on insecticide labels,” she said.
Control options can be found on http://services.apvma.gov.au/PubcrisWebClient/welcome.do.
For identification of common armyworm refer to http://thebeatsheet.com.au/armyworm/avenge-of-the-caterpillars%e2%80%a6/ or pic.twitter.com/T9ZVw4nLTF. For more information visit The Beatsheet at http://thebeatsheet.com.au/armyworm/armyworms-defoliating-sorghum-millet-and-corn-on-the-downs/.
Elise McKinna, DAFF Media & Communication Officer
07 3087 8576