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Rules To Grow Midge-Tolerant Wheat

— TODD HYRA

“We estimate use of a resistant variety will prevent $36 per acre of damage.”

Midge tolerance is probably the most exciting technology advancement in wheat in the past 50 years,” says Todd Hyra, the western Canadian business manager for SeCan. Hyra is part of the Midge Tolerant Wheat Stewardship team, a group that’s working to make sure farmers recognize the importance of maintaining this trait. The trait is very effective at killing the feeding larvae, he says, and it’s also very cost effective control for farmers, two good reasons why growing the tolerant varieties require an extra bit of effort on your part.

“We estimate use of a resistant variety will prevent $36 per acre of damage,” he says, making mdige an economically significant pest for sure. Hyra says they use an average predicted yield loss of 15 per cent on 40 bushel per acre yield at $6 per bushel of wheat to come up with that number. In many cases, that loss is conservative — 50 per cent yield reductions are not uncommon under heavy infestation.

The tough thing with controlling midge, Hyra says, is that they’re tricky to scout for and it only takes one adult per four or five heads to do damage. “Spraying also takes out beneficial insects,” he says. Midge levels can be kept in check by having a healthy number of beneficial insects out in the field.

NEED TO PROTECT SINGLE-GENE RESISTANCE

This naturally occurring, non-GMO midge tolerance stems from a single gene — Sm1. Because resistance is based on a single gene, any midge individuals that aren’t affected by its expression would soon be fruitful and multiply. If two such midge multiply, their offspring would also be unaffected by the Sm1 resistance. The Midge Tolerant Wheat Stewardship team wants to keep these midge numbers down for as many years as possible. Hence the varietal blends, which combine a midge-tolerant wheat variety in the same seed lot as a similar variety without the Sm1 gene.

“If we manage the trait with interspersed refuges we could maintain this gene’s effectiveness for as much as 90 years,” says Hyra. Misuse the trait by seeding only tolerant varieties on every inch of a field year in and year out and the midge would likely overcome the tolerance within a decade. “This is the only known (tolerance) gene out there,” he says.

Each new variety with the midge tolerant trait will only be sold as a blend. Seed lots will be sold with 10 per cent content of another susceptible variety, ensuring the susceptible variety is spread evenly throughout the field.

This allows some midge to survive and breed with those midge unaffected by the Sm1 gene, Hyra says. The resulting offspring are susceptible, for the most part, and the population of susceptible to non-susceptible midge should remain in balance.

THE VARIETIES

The Sm1 gene has been bred into three lines commercially available this year and in a fourth that will be available in 2011. “These aren’t agronomic weaklings, either,” Hyra says, noting that the usual yield or quality tradeoffs that can occur when breeding in a specific trait don’t apply here.

AC Unity VB (blended with AC Waskada), AC Goodeve VB (AC Intrepid) and AC Glencross VB (AC Burnside) are available this year. AC Fieldstar VB (AC Waskada) will be commercially available in 2011. The VB stands for varietal blend and will be noted in the name of all midge tolerant varieties. The variety in brackets will be blended in at a 10 per cent rate.

AC Unity (CWRS) is an awned variety that yields 16 per cent better than AC Barrie and offers some sawfly resistance because of a partially solid stem. AC Goodeve (CWRS) is an awnless variety that yields eight per cent better than AC Barrie and matures two days sooner. AC Glencross is an extra strong variety. Manitoba growers might be especially interested in AC Fieldstar once it’s available in 2011, as it yields 10 per cent higher than AC Barrie and has a fair fusarium rating, the same as AC Barrie. Contact your local seed dealer or any provincial seed guide for full details on each variety. Hyra estimates that seed cost for 2010 will be a bit pricey — in the $13 to $14 per bushel range — due to availability. That cost should decrease as seed supplies improve each year.

STEWARDSHIP AGREEMENT

All farmers who choose to grow any of these blends will be required to sign a stewardship agreement that allows for only one year of farm-saved seed. After that, it’s time to buy certified seed once again. That’s because over time, the crucial 10 per cent susceptible crop will diminish in the mix, allowing midge unaffected by the Sm1 gene to once again multiply.

The stewardship agreement is pretty straight-forward: it’s a two-page document outlining your responsibilities as a farmer and what happens if you save seed after the second year. It’s got some teeth, Hyra says, for good reason. Farmers found to have planted seed saved from beyond the first year will face damages of $100 per acre of seed grown and will be on the hook for any damages, audit costs and legal fees.

Hyra is confident that if enough farmers choose to grow midge tolerant varieties, we could see infestations become less severe or less often. “It could mean that because we’re using less insecticide year over year we end up maintaining the beneficial insect population that will then keep the midge in check for us,” he says.

For more on the midge stewardship agreement or midge tolerant varieties visit: www.midgetolerantwheat.ca.

Lyndsey Smith is a field editor with Grainews in Lumsden, Sask. Email her at [email protected]

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