As growers in across Australia gear up for the third season with fall armyworm, the lessons learnt from the past two seasons will play a critical role.
Fall armyworms are insect pests first detected in Australia in early 2020.
The pest quickly spread through Queensland, the Northern Territory and Northern Western Australia before being detected in NSW in September 2020.
The pest quickly spread to all the critical summer cropping regions of NSW, including The Hunter, Northern Tablelands, Central West and Riverina districts.
The larvae of fall armyworm cause significant damage to crops and are a severe pest of maize, sweet corn and sorghum.
NSW Department of Primary Industries senior research scientist and entomologist Dr Lisa Bird has worked closely with the industry since the first identification of fall armyworms in Australia.
The species is highly invasive due to the sizeable migratory capacity of the moths, with adult moths able to travel up to 100 kilometres per night.
"This means they can spread very easily outside their permanent distribution range," Dr Bird said.
Warm, wet conditions preferred by fall armyworm
Climate and weather are key drivers for fall armyworm, with the pest preferring warmer, humid and wet conditions.
"Given the season is looking good in terms of water availability and optimism around cropping, we expect that FAW will establish in farming landscapes throughout NSW again this coming season," Dr Bird said.
"Dairy production regions on the north coast and in the south-east are known hot spots for FAW, and producers are urged to be on alert for any signs of activity."
Matt Thompson, of Mid North Coast Agronomy, Bodin, NSW, has worked with producers in the area, especially dairy farmers, to deal with fall armyworms since the outbreak.
Since the first detection in NSW, Mr Thompson and his clients have learnt how to deal with the pest to reduce crop damage effectively.
"We are fortunate here as there is no overwintering; it's too cold, so we don't have the 365-day lifecycle," Mr Thompson said.
Other areas of Australia are not so lucky, with the pest thriving in tropical and subtropical regions of Queensland and the Northern Territory year round.
Dr Bird said populations had built up in northern Australia in the past couple of years.
"We then see season seasonal migratory dispersal of moths into southerly growing regions like southern Queensland and northern NSW, starting early spring," she said.
Migrations of the pest coincide with plantings of summer cereals in many regions, resulting in potential outbreaks during the critical establishment phase of crops.
The most apparent sign of FAW being present is the damage they cause to the leaves of maize and sorghum plants.
"The problem is that when larvae get into the whorl of the plant, they become concealed and therefore much more difficult to control with insecticides," Dr Bird said.
Mr Thompson said that within the North Coast region of NSW insect pressure was reduced by a few factors, including the climate and variety of crops grown.
"Not every farm has corn and there are usually big distances between neighbouring crops, corn is the major crop we see impacted by the pest, they don't tend to like pastures and soybeans as much," he said.
Diversification and beneficial insects
The biggest strategy Mr Thompson utilises with his clients is diversification and the use of beneficial insects.
"Beneficial insects, mostly sucking insects, are a major tool used to attack the pest and limit the population in summer," Mr Thompson said.
Insecticides are another control option with many registered for use on FAW, however, Dr Bird urges farmers to be cautious in their insecticide usage.
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Mr Thompson said it was important to realise that just because a product was registered, it did not mean it was going to provide effective control.
"Some products might actually be doing more harm than good," he said.
Research by the DPI has shown that broad-spectrum products such synthetic pyrethroids are ineffective on FAW as the insects carry resistance to these products.
"By using these products you can destroy the one thing that will actually help suppresses populations, which are the naturally occurring beneficial insects present in the crop," he said.
Mr Thompson said insecticides could be an issue in wet conditions, and timing of application was a critical factor.
"Insecticides can't be sprayed regularly and in wet conditions when we can't get on paddocks to spray, relying on insecticides can mean that we can't control a population at the right time," he said.
The use of selective insecticides is recommended in some cases as these do not pose any risk to the beneficial bugs present in the crop.
"Using selective insecticides allows the beneficial insects to clean up any bugs that remain," Mr Thompson said.
"At the end of the day we need to protect those beneficial insects and allow them to do the work rather than insecticides.
"If insecticides kill out those beneficial insect populations there will be no competition when FAW hatch again.
"If sprays are warranted, then it's best to use a timely application of a selective insecticide to optimise the cost of control."
Another option of control is the use of viruses that affect the FAW population.
"Viruses against the fall armyworm can be applied with pivots, boomsprays and drones," Mr Thompson said.
Another important control factor was soil and crop nutrition.
"If a crop is not healthy and resilient, we will see more damage," Mr Thompson said.
With heavy rains and the cost of fertiliser, Mr Thompson said it was important that people invested in crop and soil nutrition.
"The cost of fertiliser is high and it's harder to get on the crops but we have to make sure people are still investing in nutrition, otherwise we will see a lot more damage when it gets warmer," he said.
Some growers in the region have moved to manure compost, chicken litter or feedlot manure as an alternative fertiliser.
"Due to the forecast of more wet weather, people are opting for slow-releasing nitrogen sources," he said.
"If growers are using traditional nitrogen fertilisers and it is too wet to apply then the crop will be much more susceptible."
Another management strategy utilised in the North Coast region is the timing of sowing and harvest to align with the life cycle of the pest.
"Growers are sowing early, usually in late September and October whilst temperatures are still low and no adult moths are present, we then harvest early, usually before February/March when the population seems to be high," Mr Thompson said.
"We are not aiming for eradication but limiting the damage. FAW are present but damage over the crop is 5-10 per cent, usually less than 5pc."
The DPI recommend that all growers monitor crops regularly and be on the lookout for any early signs of damage such as windowing and shot holes in leaves.
This should include in-crop monitoring for the presence of larvae.
"Small larvae can be difficult to identify, growers are encouraged to keep suspect larvae on host crop leaves until they can be easily identifiable by clear photographs of the head and tail sections."
Local Land Services will be rolling out a program of moth surveillance in NSW this spring and this is an important step in proactive management of FAW because it gives growers early warning of any localised moth activity and it means growers can be on the front foot for managing any outbreaks. People can get involved by contacting the LLS in their area
Any NSW farmers who suspect fall armyworm on their property should email images with their name, location, crop type and phone number to fallarmyworm@dpi.nsw.gov.au.
For more information go to: https://www.dpi.nsw.gov.au/biosecurity/plant/insect-pests-and-plant-diseases/fall-armyworm.
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