Those chemicals most difficult for farmers to obtain appear to be glyphosate and trifluralin.

Elders senior agronomist Rob Harrod said the COVID-19 pandemic had also had a significant impact on supply lines.

"There was a complete stock-out of trifluralin earlier on and that hasn't been re-supplied since then," he said.

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"There's been a couple of things I believe. My understanding was this was partially from the COVID-19 situation.

"When that started up a lot of production of tech' was ceased."

Mr Harrod said some manufacturing had resumed, but new stock was unlikely until April.

"We had the big rain up north and that sucked a lot of glyphosate and I believe trifluralin since," he said.

Walla-base agronomist Tim Paramore said the shortages had created "a lot of concern" among producers in the area.

"Elders in Wagga, for instance, haven't got any Roundup left," he said.

"There seems to be some confusion over resupply, about how much longer it will be before the new orders are filled."

Mr Harrod said another issue stemming from the recent late-summer rains - falls right across the southern Riverina were plentiful, up to the 100mm mark in eastern parts - was substantial weed growth.

"We've obviously had a bad bindii year and the summer grasses are in," he said.

"We've done a lot of summer spraying for that and that puts a big strain on the reserves of glyphosate that we've been living hand-to-mouth with.

"We're over that period, the next issue is sowing. You've got people going again with a knock-down product like a glyphosate-based product before sowing and mixing it with these pre-emergent herbicides.

"All these pre-emergent herbicides are under a little bit of pressure supply wise.

"We'll just be thinking on our feet all year, changing programs."

While the rain replenished critically dry soil moisture levels, Mr Paramore said there had also been considerable infestation with summer weeds such as bindii and Bathurst burr.

"A long dry spell tends to break down a lot of hard seed and so you get germinations where you never thought you had weeds."

But both agreed the early start to sowing was a tremendous outcome for producers, with possibly more rain next week that Mr Paramore said was "going to lift people's spirits a lot".

Mr Harrod said he was fortunate he could "drive around paddocks looking" without having face-to-face contact with people "because the last thing I want to do is stop farmers farming".

"It's going to be a year of challenges trying to get things done," he said.

"But so far it's looking pretty good."