Property: Merriwa Pastoral Company
Owners: Bronwyn and Geoff Hunt; Karen, Bill and John Fenton
Area: 1484 hectares, 1436ha cropping
Location: Normanville, Victoria
Average annual rainfall: 320 millimetres
Soil types: duplex, clay loam over clay
Soil pH: 8 to 8.5
Crops grown: Scepter wheat, Spartacus barley, Stingray canola, Hurricane and Jumbo 2 lentils, Winteroo oats for hay, Morgan and Twilight field peas for hay
It’s spring 2019 and Normanville grain grower Bronwyn Hunt is marching up and down the rows of Hurricane lentils and Scepter wheat, vigorously swinging a sweep net in search of insects.
Every so often Bronwyn stops to peer into the net to see what she’s caught. There’s a variety of critters: ants, flies, beetles, spiders and larvae. Some go back onto the ground, while others are placed carefully in small jars and tucked into her pockets for closer examination indoors.
Monitoring is an important component of integrated pest management (IPM) and something Bronwyn relishes. Most mornings she does the rounds of a series of pitfall traps to “find out who’s wandering around at night”.
Bronwyn says her interest in IPM was piqued at a Birchip Cropping Group workshop run by South Australian entomologist Judy Bellati about a decade ago.
“It was absolutely eye-opening,” she recalls. “At this workshop they showed us what the particular bugs were and talked about beneficial insects. No one had ever talked about beneficials before. They are amazingly important and that’s when I began observing things more – I could see that using the beneficials as a tool is quite important. The trouble with spraying insecticide willy-nilly is that you kill the beneficials and often you can get a rebound of the pests. I’m now very loath to use an insecticide unless there is a very good reason for it.”
Bronwyn started by monitoring canola, which has been a good break crop and grows well once it gets going, but is highly susceptible to damage during germination and establishment, when up to 50% of the crop can be lost.
“The problem is, it puts its cotyledons out and if anything removes those, the plant’s dead,” she says. “All our other broadleaf plants, which are legumes, if something takes those first true leaves, it just shoves some more out from down below. Canola doesn’t have this capacity. If you have pests that are removing those true leaves, you lose those plants.”
Bronwyn uses pitfall traps and sticky paper to catch insects, as well as a system she invented using skewers and surveyor’s tape to identify losses among the tiny plants.
“When the canola was coming up, I’d put a skewer with a bit of surveyor’s tape on it in one spot and I’d count 20 plants and put another one in,” she says. “Then I’d go and look every morning. If I count 20 plants and moved the skewer in (closer) there were more plants up. If I count 20 plants and moved it out, it meant some of those plants were disappearing. It’s very hard to see canola disappearing because often the little cotyledons are taken just before or just as they’re coming out of the ground.”
Monitoring showed the presence of pests such as false wireworms and brown beetles, but insects weren’t the only culprits: mice were also to blame, especially in drier years when germination was uneven.
Bronwyn says imidacloprid seed dressing has been revolutionary, especially for protecting against mites and aphids in canola and Russian wheat aphid in cereals, because it “only gets the guilty”. But she can’t help wondering about its long-term effects on beneficial insect populations.
“I’ve found some beneficials like the carabid beetles that are a bit twitchy,” she says. “I’m not sure if that’s secondary poisoning because there have been a lot of insects eating my canola; it would be interesting to find out.”
Over a decade of observation, quantifying just how much damage insects cause, how much it costs, and learning how effective beneficial predatory and parasitic insects can be, Bronwyn says they’ve significantly cut their use of insecticides on the farm. They now only spray with selective pesticides when absolutely necessary and have adopted other methods of prevention, such as controlling summer weeds which can harbour pests and choosing a rotation that provides for pest breaks as well as disease breaks between susceptible crops.
“In latter years with the pitfall traps I’m almost always finding only beneficials,” she says. “This year, I only found ants, spiders, and carabid beetles. They’re voracious and can consume a huge amount of insects so you really don’t want to be doing them in.”
Bronwyn flicks through a well-worn copy of the Grains Research and Development Corporation handbook Insect ID: The Ute Guide as she lists all the beneficial and benign insects found on the farm: from spiders of all sizes to termites, wasps, hover flies, ladybird beetles, damsel bugs and lace wings, as well as the tiny orange French anystis mite that eats red-legged earth mites and lucerne fleas.
Army worm and cut worm levels have been too low this year to warrant treatment, but Bronwyn concedes they will likely spray the lentils against Etiella moths when they arrive in a month or so.
“It is a problem because the market for lentils has very close to nil tolerance for grub damage,” she says. “In most of our crops, I like to see the whites of the eyes of anything out there first and then I like to make sure there’s enough that the economic damage warrants spraying. Lentils is the only thing we definitely will spray because the food market has no tolerance for grub holes.”
Spraying cabbage aphids on ripening canola is now a thing of the past.
“It doesn’t actually affect the yield very much because it only gets those last few flowers and it’s the hotter part of the year, so you don’t get much from those seeds,” Bronwyn says. “The cost of the operation would be much more than the actual spray and that’s part of the problem – when people can put it out so easily and quickly because they throw it in with their weed or fungicide spray.”
IPM helps guard against the development of insecticide resistance caused by overuse or misuse of insecticides from the same mode of action group. Resistance in Australia has so far been identified in red-legged earth mites, green peach aphids, diamondback moth and corn earworm.
The trouble, Bronwyn says, is that insecticides used to be quite expensive and farmers would only use them if there was a serious problem.
“They’ve gotten quite cheap and a lot of agronomists will say ‘You’ve got to put out that herbicide, so you might as well put an insecticide out’,” she says. “It kills everything, good and bad. They really don’t know what (damage) they’re doing. It might be cheap in terms of dollars for that paddock but it’s quite expensive for what else is out there.”
Bronwyn sees the time commitment required for regular monitoring as another barrier to the adoption of IPM by more farmers.
“It’s very time consuming,” she says. “I’m lucky I can whiz out there and do it. A lot of blokes just don’t have the time to do it and that’s why they just throw a bit in (the sprayer) because it seems easier. You can see what it costs you if you don’t control the pests, but you can’t see what it costs you when you kill all the beneficials. Not many people are going to buy this message. I find insects absolutely fascinating, but not everyone’s like that.”
Project: ‘Supporting the sustainable use of insecticides and adoption of IPM in the southern grain region’
Project Funder: The GRDC
Project lead: Kelly Angel, BCG