Diquat loss puts greater focus on spray timing

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- CPM (Crop Production Magazine)

Darryl Shailes says that even though there are alternatives to diquat for early season weed control, growers will have to be more proactive about timing sprays accurately to get the best results and avoid compromising crop safety.

Darryl Shailes

The main contact-acting foliar options for pre-emergence broadleaf weed control are products based on carfentrazone-ethyl (as in Shark) or pyraflufen-ethyl (Gozai). “Adding 1.0 l/ha of Roundup Flex (glyphosate) can provide effective grassweed control where needed but take care and read labels because not all glyphosate has approval for pre-em post-planting use,” he highlights.

Metribuzin, prosulfocarb and metobromuron, while having some contact activity, will generally need bolstering from a contact material if many emerged weeds are present at the time of spraying.

“We’ve seen comparable results to diquat from these kinds of mixes, so the biggest issue for most growers will be timing,” says Darryl.

Many growers are applying diquat up until 10% crop emergence, which can cause some chlorosis (yellowing), but effects are generally not too severe. However, he warns that crop effects from products like Shark and Gozai can be much greater when used at a similar early post-emergence timing, and although crops will recover, growers must be careful not to push the timing as potatoes will be burnt back to the ground.

To minimise risk, he recommends applying herbicides before the crop emerges and the ridges crack. This is absolutely essential if using Roundup Flex in the mix, he adds.

“This may well mean prioritising the first treatments to particularly vigorous or quick-establishing varieties to avoid getting into a post-emergence situation,” he notes.

Using higher water volumes to improve coverage over the ridges is also important for maximising herbicide efficacy, says Darryl, who suggests growers should be using water rates of up to 300 l/ha.

This, combined with using forward and backward-facing nozzles, should help reduce shading effects on ridges and improve overall weed control, he says.

Finding effective alternatives to diquat at either end of the season is just one of many agronomy areas under investigation at the Hutchinsons Fenland Potato Demonstration site near Mildenhall in Suffolk this year.