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Soybean School: Being “fashionably late” with a pre-harvest burndown

By: RealAgriculture Agronomy Team

September 7, 2021

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When it comes to applying a pre-harvest burndown, getting in the field for an accurate pod assessment is crucial. When a harvest aid is applied at the appropriate time, it can work quickly.

On this Soybean School episode, Bernard Tobin is joined by BASF agronomist Ken Currah in the field to talk staging soybeans for a safe and effective burndown application.

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In the area of the field Currah is standing in, 90 per cent of the pods have changed colour, and there’s a bit of a green tinge to the top pods, and everywhere else in the field, the plants have yellowed and are heading to maturity.

“We always look at pod colour change staging first,” says Currah. “The leaf drop number is kind of a coincidence — it’s usually 70 to 90 per cent — but what I tell agronomists and growers is don’t fall in love with the leaf drop levels, and what you’re seeing in the field at a distance. You have to look at pods to properly stage your burndown.”

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The disclaimer right up front for any grower, especially those growing IP soybeans, is talk to the buyer or contract holder, to know what’s permitted in terms of glyphosate use, says Currah.

As for pre-harvest intervals, Currah says it’s better to be “fashionably late,” especially when the pre-harvest aid is applied properly, in good conditions. Adding glyphosate can push the pre-harvest interval days up, but that’s still a short amount of time from application to harvesting.

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“If we’re too early, we risk leaving some green in those top, later developing pods,” says Currah. (Story continues below video)

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White mould was widespread this year and soybeans got quite large this year. Currah recommends 20 gallons of water or more per acre, to even out the diseases pockets of the crop for more even burndown.

Proper environmental conditions are crucial for this type of application, ideally in the heat of the day with lots of sunshine. “We want plants and weeds to be actively growing, they’re opened up to take that chemistry in,” says Currah.

High water volumes with the proper surfactant, as well as slowing down the travel speed, all ensure as close to optimal an application as possible.

Currah’s final tip is that desiccation is not weed control — by now, weeds are mature, have gone to seed, and have become woody, and at best a burndown application will prevent viable seed from entering the seedbank. But desiccation timing can also be an opportunity to weaken perennial weeds as they’re shutting down and translocating nutrients.