Gerri the NVT Guru covers how to identify fall armyworm and manage infestations in Australian crops. The video explains distinguishing features, economic thresholds for treatment, and biological control methods to protect your plants.
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So fall armyworm, now an endemic species, was an exotic species until 2020 when it arrived, has spread across, you know, all of Australia, including Tasmania and Norfolk island, and has been having a major impact on maize, sorghum, French white millet and then also port horticultural crops. I've been quite surprised by how destructive it is. When it first turned up, you know, I thought, oh, it's another noctua. You know, we've dealt with lots of noctuids before Helica verpa, the native armyworm species. It'll be all right. We're used to dealing with Noctuids, but, gosh, this one really is very, very challenging. The things that really do distinguish fall armyworm are the dots on the back the body. As they get bigger, they get darker and more pronounced on the head capsule. If you were to use a hand lens or something, you can see that the head capsule is mottled and then there's an inverted Y sort of between the eyes on the. On the front of the head. There's some behavioural things about them. You know, they want to get away and get out of the sun. Helica RPA are not so fussed about that. And then the native armyworms will tend to curl up in your hand, whereas fall armyworm don't tend to do that quite so much. Helica verpa, very aggressive. Fall armyworm not so much won't spit on you like Helicoverpa do. So, you know, these little things that people will learn from the experience help them to distinguish them as well. In terms of crop monitoring, I guess people are tempted to try and make a decision based on the damage that they can see. It really does do the decision making a disservice trying to do that, because what you see when you look at damage is what has already happened, not what's going to happen. You can't recover the damage that's been done, but you can prevent further damage from occurring. In my opinion, it's absolutely critical to do destructive sampling, not just look at damage. To do a really effective destructive sample, I guess you need to pull the plant out of the ground. For the most part, fall army worm are confined to that whorl in the upper leaves. So I guess the way we go about it, because we want to know whether there are eggs and, and whether they're a small larvae and whether they're a bigger larvae. So, you know, you sort of examine the plant looking for eggs, which will largely be under the leaves, and then you can just pull the lower leaves away Break the whorl off and unfurl that and the larvae can be anywhere in those leaves that make up the whorl. There are a number of second, third instar larvae here already and just keep going, making an account of those. So that's two mediums and I think three smalls in that one. In the assessments that I do, largely I won't count the very small larvae. The mortality of those small larvae is likely to be extremely high. Fall armyworm is one of those pests where to make good decisions about what the loss might be good going forward. You're really interested in which larvae are establishing so that are medium or bigger. You can't really make very good decisions on those very small larvae because the majority of those will disappear. In terms of, you know, using that information about what you find in making a decision. I guess we're still waiting for the outcomes of the threshold work to be finalised. We were very fortunate when fall armyworm arrived that the Queensland government made a substantial investment that allowed us to respond to the initial outbreak and I guess the complete unfamiliarity of growers and agronomists to managing this pest. And one of their priorities was economic thresholds. And the grains industry is used to having economic thresholds to guide their decisions. So GRDC came on board and has made an investment in the development of economic thresholds for sorghum and maize. This plot has had damage up until 10 leaves and then it was treated and you can see the new growth that has started to come out undamaged by fall armyworms. So I guess gives growers the confidence that you can have, you know, sort of quite ugly looking damage. But a plant that still has the capacity to put out new leaves and fill grain, The conventional chemistry that's available is extremely effective. It's been proven to be so even under the really high density that we've seen this year. So unfortunately, you know, the mainstay of fall armyworm control will be insecticides for the short term. But over the last four years, we've been doing a lot of survey work looking at what else is there in terms of biological control control, what other pathogens, what parasitoids and predators. And it's been, you know, quite incredible to see just how many things are taken on fall armyworm, from, you know, egg parasitoids like Trichogramma through to the predatory shield bugs that turn up when they're great big larvae and feed on those. So I think that, you know, it's really important that people give that some consideration, particularly in Seasons like we've had the previous two years, where the populations were sort of low to moderate and all you needed to do was just keep a lid on that. And that's, you know, the perfect opportunity for natural enemies to be included in the management. Minimising the risk of having a damaging fall armyworm infestation seems a little bit more possible now that we understand that the fall armyworm populations in different regions tends to build up as the season progresses. So from 2020 through to 2023, we ran a network of pheromone traps across Queensland. As a result of those insights, growers, particularly in terms of maize, have moved their plantings as early as possible. And those early plantings, so at the beginning of the sort of planting window, if you can get your crop in there, in almost every region, that crop will come through without seeing major fall armyworm impacts. This plot here probably is very likely to have incurred a yield loss just because of the reduction in the canopy size during the vegetative stage. But, you know, still a crop certainly, you know, from Central Queensland south, real opportunities to try and get your crops in early to avoid the build up. As summer progresses, Central Queensland is a bit more challenging because of course they're, you know, they're sorghum planting window falls straight in that, you know, sort of high pressure period. So it's at this point not really clear what their opportunities are and I guess that needs a little bit more thought.
