A BUGOLOGY expert says the chances of another outbreak of Helicoverpa armigera in wheat and barley this year are not considered likely and new research has provided a better understanding of their impact.
Melina Miles of the Department of Agriculture and Fisheries provided attendants of the GRDC Updates in Westmar with an insect pest management update focusing on rutherglen bug in sorghum and Helicoverpa armigera in wheat, which presented a number of challenge.
Due to Helicoverpa armigera’s resistance to synthetic pyrtheroids and carbamates, the products couldn’t control infestations and the registered insecticide options were older and it is now resistant too.
This combined with an insecticide shortage and delay in detecting infestations until large larvae were visible on the heads, made it even more damaging.
The outbreak prompted a QDAF Entomology trial at St George to assess the impact of the Helicoverpa armigera larvae on wheat.
It found the bug was causing twice as much damage to wheat as it did on chickpeas and sorghum.
“It was really a coincidence of the very late wheat crops and the high Helicoverpa armigera activity in spring, that combination is why we had the issue last year,” Ms Miles said.
“You can already tell that crops aren’t as late as last year.
“What we didn’t know is how much damage they could cause and the difficulty to detect, most people saw large larvae and by that time they were really hoeing in.”
The trial found beatsheet sampling detected less than 10 per cent of small helicoverpa larvae in the wheat crop canopy and that if another outbreak was to occur, evidence of leaf feeding, was the best form of inspections.
Based on a consumption rate of 24kg loss/larva/square metre, it is now suggested that a breakeven threshold for helicoverpa in wheat is 3-5 larvae/square metre.
“If we get this situation again, look for this sort of feeding, more of a grazing on the leaf’s surface,” Ms Miles said.
“If you start to see that in the canopy when you’re looking for leaf diseases or various other things, it would be worth then getting out your beatsheet and giving that crop a really good shake to see what comes out.”
Rutherglen bug
Another bug seriously impacting crops last year was the Rutherglen bug and new research has found a commonly use insecticide isn’t as persistent in combating the problem.
Ms Miles said she believed Rutherglen bug numbers were the highest and most persistent since an outbreak in 2007.
“Rather than being around and coming into crops for say two or three of four weeks they are now there for two or three or four months,” she said.
“I think this is probably a function of relatively good seasons with hosts being present in our cropping areas, in close proximity to our crops.”
Ms Miles received large number of phone calls from growers frustrated that applications of alphacypermethrin were not lasting longer than a few days and so screening trials began looking at chemicals when sprayed directly onto adults.
A crop was sprayed with products and bugs were introduced at different time periods.
The tests found alphacypermethrin rapidly deteriorated after three days.
“Alphacypermethrin is probably the least persistant,” she said.
“It might work on midge but it doesn’t necessarily work as well for other pests.”
Lucy Kinbacher
Raised on a cattle property at Biggenden, Lucy Kinbacher has spent 10 years working across metropolitan, regional and rural publications in both Queensland and NSW. Lucy has been the editor of the Queensland Country Life and North Queensland Register since 2021.
Raised on a cattle property at Biggenden, Lucy Kinbacher has spent 10 years working across metropolitan, regional and rural publications in both Queensland and NSW. Lucy has been the editor of the Queensland Country Life and North Queensland Register since 2021.
