Fall Armyworm’s ability to adapt putting more crops at risk

Date:07-18-2024

The word ‘challenge’ dominated talk among researchers, government officials, grain and cotton growers, and fodder and vegetable producers at the National Fall Armyworm (FAW) Research, Development and Extension Symposium in Brisbane in April.

However, Simplot NSW agricultural manager Evan Brown had the most descriptive analogy of FAW’s destructive path: ″It is like the Cookie Monster.″

Its fondness for sweetcorn in particular has seen Simplot – an agricultural and food manufacturing business – move production from Bundaberg, Queensland, to New South Wales. It has developed an integrated pest management strategy for the company’s own farms and its 30 contract growers.

About 300 kilometres inland from Bundaberg, Theodore-based cotton and grain consultant Damian Erbacher also spoke of changing tactics in response to FAW. Maize plantings have moved from February to July: ″My biggest fear is that it will adapt to cold conditions,″ he told the symposium.

The face-to-face forum was held to build cross-collaboration between industry, government, researchers and funding bodies. It aimed to share learnings and identify priorities.

Since it was first detected in northern Queensland, the Northern Territory and Western Australia, FAW has spread swiftly. It is now in Victoria and a scientist at AgResearch NZ, Scott Hardwick, also confirmed its presence in New Zealand.

Globally, it is considered the plant world’s ‘foot and mouth disease’, said biosecurity specialist Chris Dale from the Federal Department of Agriculture, Fisheries and Forestry. Understanding the effects of FAW, the Food and Agriculture Organization (FAO) took the unprecedented step of developing  a global action for the pest in 2020.

Since then, global action technical working groups have been established.

Fall armyworm is continuing to prove a challenge for growers and agronomists.  Photo: Rowdy Travis

Confronting conditions

Keynote speaker Dr Melina Miles, principal entomologist at the Queensland Department of Agriculture and Fisheries, set the scene on current conditions. She said 2024 had been a taxing year for those across the horticulture, grains, cotton, animal and sugar industries.

″Fall armyworm has been one of the most challenging and confronting pest management issues I have dealt with. That is partly because we don’t have answers. In outbreaks of other pests, there has been at least some local experience and information to go on.″

Its persistence has shown it is not just another pest caterpillar.

″We may not yet have seen the full extent of FAW’s impact.″

The pest has had a major impact on grain and fodder maize; grain and forage sorghum; white French millet; early sown oats and barley; sugarcane and Rhodes grass at establishment; and crops such as strawberries, capsicum and ginger.

″We are uncertain of what its impact will be on mungbeans, soybeans, pigeon peas or peanuts.″ After a difficult summer, Dr Miles said it was to her ″absolute horror″ that FAW was found to be infesting and severely damaging early sown winter cereals.

″That changes the playing field. Not only are traditional grain growers affected, but also the fodder producers, those dairies that grow for themselves, and the beef producers who are filling an important feed gap in their programs.

″They are now in a position where they have winter cereals that are being severely impacted and no options legally available to them to control those populations. These are the practical realities we are dealing with. And for the growers, and their advisers, it has been a very steep learning curve.″

Future options

While it is challenging, Dr Miles outlined future options, saying that to date decisions have largely been reactive and, with time and resources, could be more proactive.

″We’ve been so focused on preventing crop loss and grower education that we haven’t had the time to sit back and think about structural fundamentals. What contributes to the challenges we face in the field in a moment?″

She said a better understanding of population dynamics and an area-wide approach to collaboration across industries, crops and seasons would help.

″Are there ways to manipulate those populations to minimise the roller-coaster that we currently experience with infestations, treatment, reinfestations, treatment? I think we can come together across industries and farms to squeeze every opportunity out of the management of FAW.

″We don’t want to be stuck just intervening with insecticides.″

She said Dr Joe Eyre’s work on crop recovery, plus the undervalued contribution  of integrated pest management, would help.

Dr Eyre, a University of Queensland crop physiologist, is working with Cesar Australia research scientist Dr Alex Slavenko to build a dynamic tool that predicts yield losses using FAW population density and sorghum crop stages.

FAW reduces canopy size, which means less light is transferred into sugars, and that equals fewer grains.

Evolving tastes

While maize is a firm favourite for fall armyworm (FAW), it will infest other crops and can evolve its tastes.

Queensland Department of Agriculture and Fisheries (DAF) research scientist Trevor Volp has been undertaking glasshouse experiments on sorghum, peanuts, pigeon peas, cotton and maize.

His research shows that not only does FAW prefer maize, but it also performs better on a maize diet. ″After only five days, the larvae are twice the weight of those that are feeding on sorghum.″

However, while FAW prefers maize, if there is no other choice it will still reach the pupae stage on non-preferred crops. This puts intermediate species such as winter cereals at risk.

FAW’s ability to evolve is also concerning, he said, explaining a laboratory experiment in China.

It involved taking a FAW population from a maize crop and keeping one half on maize for 20 generations and the other half on rice for 20 generations.

Preference and performance tests were undertaken every few generations. ″It took the rice-fed FAW just four generations for its preference to switch from laying eggs on maize to laying eggs on rice.

″I think this capacity to change is important to flag.″

Mr Volp also spoke about carbon isotope research identifying FAW’s dietary habits and how it is shifting from maize and sorghum to winter cereals.

″A couple of years ago I would have predicted that the carbon isotopes would show that the most moth populations are generated on C4 plants, like maize and sorghum. But from moths collected in September and October last year, we found almost 50 per cent of our samples had fed on C3 plants as larvae, that is potentially winter crops like wheat, barley and oats.

″So, if we understand the feeding habits and behaviour of this pest, can we develop proactive management strategies? Can we identify what plant species generate FAW outbreaks? And additionally, can we work on host plant resistance to develop less susceptible crop varieties?″