When whitefringed weevil was wreaking havoc with Glen Ryan’s fresh market potatoes on his Quinninup farm in Western Australia in the 1990s, help was close at hand.

Together with his father Tony and brother Dean, Glen enlisted the expertise of entomologist Stewart Learmonth from the Western Australian Department of Agriculture (now known as the Department of Primary Industries and Regional Development) to tackle the problem. At the time, Stewart was leading the three-year project Soil Insect Pests of Potatoes (PT00021), a strategic levy investment funded by the potato levy through Hort Innovation.

Noting the weevil’s life cycle, Stewart and the Ryan family collected samples, discovered how and where to find the females, and devised strategies. One was to eradicate the females through sprays, but its effect was minimal. The other was to remove the food source for the larvae that don’t transform into the weevil, planting a break crop of oats between potato crops for four years.

“A small area (80 acres) was badly infested but they were still a problem over nearly all the rest of the 1,600 acre farm. Using oats, there was a significant depletion in the numbers. It didn’t eradicate the larvae totally, but it made a huge difference. The success led us to start using break crops in all fields as we could see some benefits and it’s something we’re still doing today,” Glen says.

Working with about 1,000 millimetres of rain annually, Glen said they had tried legumes as a break crop but found they were a favoured feeding crop for the larvae. Rye grass had its issues with Rhizoctonia and other diseases, and barley also had mixed results.

Quality outcomes

Seeding the oat crops up to 15 months before planting the potatoes has been the most successful formula, Glen says. It allowed the break crop to grow and then be smashed down by cattle over summer. The oats return as a green manure crop, which is mulched two months before planting potatoes.

“That’s made a huge difference to the healthiness of our soil – turned it right around – and it has had a big bearing on the operation of our farm,” Glen says.

“In our situation, the break crop works really well – not just for taking out the whitefringed weevil but also Rhizoctonia and nematodes to some extent. So, there’s a broad-spectrum effect that’s not just a one-off.

“We’ve been doing that for 10 to 12 years, actively using soil amendments and ameliorants that are microbe- and bug-friendly. The clay is pretty close to the surface in some places – it may only be 75 millimetres below the surface. But going down this path has meant we now have top soil in our paddocks that is double or triple that.”

The project also addressed the “big problem” of African black beetle.

“They are tougher to control and we still use chemicals to control them, but the break crop certainly helped in reducing those numbers,” Glen says.

Keep talking

The collaboration with Stewart led to the formation of a Manjimup and Pemberton potato growers group, which travelled to Tasmania to study soils.

“The information transfer was fantastic and some of their guys have been over here since,” Glen says.

“Collaboration opens up your mind. We went over there and saw a lot of things, we talked and found out more, and saw some things we could implement to make the soil as strong and vibrant and healthy as we can. That’s led to the green manuring, compost and soil ameliorants.

“It all sounds like smooth sailing, but we’ve made a lot of mistakes along the way. You’ve got to keep trying things and talking to growers. There’s a lot of knowledge out there; you’ve just got to source it.”