Frost and spraying delays after cold weather

A chilly week has resulted in frost across much of the State, with many towns reporting successive frosty days.

While frost damage can significantly reduce crop yield and grain quality, spraying around frosts can also create damage within the crops.

A CropSmart agronomy update said ideally, plants need to be actively growing to uptake the chemical sprayed on them, so if a crop has been partially damaged by frost then herbicide efficacy will be significantly reduced.

Common opinion is that farmers shouldn't spray 24 hours after a frost event, or 48 hours after two events.

WeedSmart estimates that twice as much clethodim is required to kill susceptible annual ryegrass if the product is applied after three days of frost.

Even higher rates are required if the plants have resistance to clethodim.

Continual frost has left Kulin farmer Bryn Davies unsure of when is the best time to spray.

"It's so cold and it's been such a staggered germination," Mr Davies said.

"We had frost today, then it was too windy yesterday and it was raining the day before that," he said last week.

"So that's why I'm picky about spraying, because I've just heard that I'm shearing in two weeks' time and I've got very little of my program done."

Radish resistance has also become an issue, surviving a few frosts, a dry start and herbicides.

This has Mr Davies more concerned about hitting the paddock at "optimal" timing.

"I've heard a lot of people are just going for it," he said.

"One bloke said to me, you're not gonna get perfect conditions, but with frost it makes it even worse."

Mr Davies sprayed on the afternoon of June 20 and for three days until it rained the following Monday which "reset" everything.

He said overnight temperatures for the rest of the week were forecasted to be around the 0°C to 2°C mark.

"It's just one of those perfect seasons," Mr Davies joked.

Merredin Rural Supplies agronomist David Keamy said he wasn't sure how well chemicals would work on frost-affected areas.

"It's got to be done, so we will just accept the result I suppose," Mr Keamy said.

Despite spraying after two or three frosts a no-no, farmers haven't been left with many options.

"We've got so many hectares, it's got to be done at some stage," he said.

"If we leave it and say, 'we'll wait till after this rain', who knows?

"It could be one degree again and you've just gone another 10 days, and the weeds are getting bigger."

Frost has been frequent, with Mr Davies believing it has been some of the worst frost he had seen in years.

"It's been very bad," Mr Davies said.

"The last week I've just had frost, frost, frost and more frost."

He said the past two years had been quite mild for frost at Kulin and he had almost forgotten what it was like to battle it.

Some crops don't appear to be growing on his farm after "brutal" frost in late June.

It was hard for Mr Davies to find the words to describe what his paddocks looked like, with the first adjectives unprintable.

He blamed the late seeding as a large factor, as Kulin was looking dry at the start of the year - and he waited as long as possible before seeding.

Unfortunately, it's a double-edged sword.

Walking around his farm in early May, the paddocks were patchy, with barley varying from six-leaf to two-leaf.

Mr Keamy mirrored this statement, with crops a few weeks behind where they should be.

Merredin was hit with -1.0°C and he said a lot of farms had been hit with a "good" amount of frost.

He wasn't too concerned about frost this early in the season as it was still early days for the crops.

Unlike further north, he said Merredin was looking "very nice" and had received 7mm for the third week of June, while Southern Cross had received about 2mm - but still had some soil moisture.

Like everyone across WA, Mr Keamy was hoping for some more rain.

A spokesperson from the Bureau of Meteorology said frosts were likely to occur when temperatures dipped below 2°C, on cloudless nights.

Over June and July this year there were 10 more days where an overnight temperature below 2°C was recorded, compared to last year.

This is due to an increase in the number of cold fronts bringing more cold southerly air events, which cleared the skies of cloud allowing for the temperature to drop and frost to occur.

These weather events are not as common this time last year.

Last weekend in Wandering the temperature dropped to -2.2°C, with the Newdegate Research Station recording -1.3°C and Collie East, York, and Jarrahwood all recording -1.0°C.

A bureau spokesperson said it was unable to record if frosts occurred during these days, however said that clear, cloudless nights typically led to a sharp drop in temperatures which resulted in frost.

However these figures are considerably different compared to this time last year, where the minimum temperatures did not fall below 4 degrees in the Goldfields region.

From July 17-23, 2022, the average minimums were much milder, staying between 4-6°C, in many towns within the agricultural regions and the Goldfields.

The average temperatures across WA have been 15-18°C in most of the South West Land Division, with pockets of colder temperatures in the Great Southern which recorded an average of 12-15°C.

From the Perth Metropolitan area up the coast line to Geraldton, temperatures have been an average of 9-12°C, with the same at Albany and Esperance.

At the start of this week much of the coastline reached temperatures between 15-20°C, while temperatures at inland towns across the regions recorded between 10-15°C.

Friday morning is expected to be below zero in some areas, however the overnight temperatures aren't expected to drop below 3°C for the weekend.