Crop protection research scientists have issued advice for Western Australian grain growers on key invertebrate pests to monitor as 2023’s winter cropping season takes shape.

The two PestFacts WA webinars were made possible by investment from the Grains Research and Development Corporation (GRDC) and the Department of Primary Industries and Regional Development (DPIRD) as part of the Integrated Pest Management (IPM) for Grains program.

Scientists discussed WA’s climate outlook and the pests that growers need to watch out for in the upcoming season, including a dedicated session on snail management for southern WA.

DPIRD senior research scientist Dr Ian Foster says rain events that occurred in late March were consistent with Bureau of Meteorology modelling.

“For a lot of the eastern grainbelt and for parts of the north, it is already wetter than average for March, but depending on how the rain arrived, there may have been significant run off,” Dr Foster says.

Overall, this autumn is around twice as likely to be drier than average, according to the Bureau of Meteorology’s rain outlook, and modelling for winter indicates it is likely to be drier than average as well.

“This doesn’t mean there will be no rain, but it’s likely rain will be patchy, and there may be big gaps between rain events,” he says.

DPIRD entomologist Svetlana Micic says that despite a dry summer, a ‘green bridge’ consisting of mainly grasses and brassica weeds was present in the southern coastal parts of the state.

The green bridge is any plant material such as crop volunteers and weeds growing out-of-season that can act as hosts of pests and diseases, allowing them to move from one season's crop to the next.

DPIRD entomologist Svetlana Micic says small conical snail management practices that can be applied in autumn include spraying summer weeds and/or windrow burning and baiting prior to seeding. Photo: GRDC

Pests that growers may need to monitor, depending on their location, include diamondback moth, Russian wheat aphid, green peach aphid, redlegged earth mite, lucerne flea, weevils, vegetable beetles, slugs and snails.

Ms Micic urged growers who see unusual pest activity in paddocks to identify pests properly before implementing spraying programs.

“If you see anything unusual in your crops, please identify it and make sure you get it right before you spray,” Ms Micic says.

“If you do choose to apply control measures, consider the pests you’re not targeting as well as the ones that you are, to reduce the unnecessary exposure of non-target pests to chemistry to which they can evolve resistance.”

DPIRD has a free insect identification service to which growers can submit photos or send samples of pests for correct identification.

In a second webinar focusing specifically on snail management, Ms Micic says management of snails required a long-term strategy, with no ‘silver bullet’ existing to eradicate snails quickly.

There are three main snails that damage broadacre crops in WA: two species of round snails (Vineyard snail and White Italian snail), and one species of pointed snails (Small conical [pointed] snail).

South Stirlings grower Alaina Smith, who also co-presented at the webinar, says small pointed snails had been present on her farm for 30 years but only noticeably caused crop damage 15 years ago. Snails were initially located around sheds and areas of exposed limestone.

“Small conical snail numbers increased 15 years ago corresponding with a larger cropping program being put in and a decrease in sheep, increased liming, increased stubble and earlier sowing of canola providing a feed source,” Ms Smith says.

Ms Micic says management practices that can be applied in autumn for small conical snails included spraying summer weeds and/or windrow burning, and then baiting prior to seeding.

“These practices ensure paddocks are bare prior to baiting and the snail has no alternative green food sources to distract them from eating the baits,” Ms Micic says.

Trial camera footage has revealed that snails are more active with higher humidity and at night, with movement less dependent on temperature.

“Growers should bait after rainfall events when snails are actively moving and feeding, and prior to the snail laying eggs, which is indicated by its enlarged albumen gland,” she added.

“This year with rainfall in late March, the albumen gland is expected to be fully developed by mid-April, so now is a good time to bait.

“Growers are required to follow the registered rate on the product label, which will also ensure the correct number of bait points for optimal control.”

Good management in autumn will decrease the risk of snail contamination of harvested grain. Seed cleaning and using a snail roller to crush the snails will effectively remove snails from harvested grain.

Recordings of the two webinars, Climate and pest outlook for WA and Managing snails in WA, will be available soon on the DPIRD YouTube channel. The PowerPoint presentations will also be published on DPIRD’s About PestFacts WA webpage.

Resources for snail management include GRDC’s slugs and snails grower resource page and DPIRD’s slug and snail control page, as well as information from Stirlings to Coast Farmers on costs of removing snails at harvest.

Growers can sign up for PestFacts WA’s newsletter, which is published as needed during the growing season. PestFacts WA is an interactive reporting service providing risk alerts, current information and advice on pests and diseases threatening crops and pastures during each growing season. The PestFacts WA Reporter App can be used to report, and request identifications of, crop pests and plant diseases directly from the paddock.