A hail storm that ripped through an avocado orchard in the Northern Rivers of New South Wales last week has destroyed an estimated 4 million avocados.

Aussie Orchards' managing director Colin Foyster said 80 per cent of the fruit on the 12,000 trees at the Pretty Gully farm was knocked off and onto the ground.

"I wasn't here but some people have said the hail stones were up to three inches [7.6cm] in size and very jagged," he said.

"It only hailed for less than 10 minutes, but [the stones were] big enough to knock the fruit off the tree or damage the remaining fruit.

"It's three months away from harvest, so it's all immature, so it's unsalvageable."

Mr Foyster said the remaining fruit on the trees also had impact marks where the hail hit the fruit, and the trees themselves were also damaged.

"If it's around the stem, or it's severe, it will lead to a rot and that fruit will then drop off," he said.

"But most of the remaining fruit, the 20 per cent, it'll just be downgraded."

It is estimated around 200,000 trays of avocados, approximately 4 million pieces of fruit, were destroyed by the hail storm. ( ABC Rural: Kim Honan )

Mr Foyster said the remaining avocados would be downgraded from premium fruit to class 2 fruit worth half the value.

"It won't go into a premium 5kg tray; it'll go into a 10kg bulk box, which you basically get the same money for," he said.

Record expected for Pretty Gully crop

Aussie Orchards is a family-owned-and-operated business with avocado, lychee, sugar cane, macadamia and vegetable farms spread across the Northern Rivers and far-north Queensland.

Pretty Gully is an isolated area, 35 minutes' drive north of Tabulam in the Upper Clarence Valley.

Colin Foyster is the managing director of the family-run business Aussie Orchards. ( ABC Rural: Kim Honan )

This year Pretty Gully was expected to deliver a record crop for the Foyster family, but instead it is believed to be one of the biggest natural disasters to hit a single avocado orchard in Australia.

"This is a 100 per cent mature orchard; the original trees are 20 years old and the youngest trees are 12 years old," Mr Foyster said.

"It's protected so we don't get the wind rub, so a high percentage of premium fruit comes off this property.

"We don't have pests and diseases like we have to put up with on our other farms and a lot of other growers have to deal with."

The 2019 crop would have produced an estimated 200,000 trays of fruit, or around 50 semitrailer loads of avocados.

Mr Foyster was devastated by the damage and the financial loss.

"My therapy is to assess the damage and get off this farm and go somewhere else for a month or two, and come back and it won't be as apparent," he said.

"But you can't beat yourself up; you've just got to move on.

"It's a bit sad for all my children, we're all partners in the business together, they've only just started in the past couple of years and they were all looking forward to our record crop. But it's not to be. They'll bounce back."

It may, however, take the orchard a little longer to recover.

"Hopefully there will be something left here for next year's crop because it's not just this year's crop that's on the trees, the fruit, it's also the leaves that you see on the ground.

"They're all the tips of where the flowers were coming for the next year's crop, so there will be a major impact on next year's crop as well."

Around 80 per cent of the fruit on the 12,000 avocado trees in the Pretty Gully orchard was knocked to the ground. ( ABC Rural: Kim Honan )

Avocado orchard survived drought and raging fire

It had been a tough season leading up to the hail storm with months and months of dry conditions in the region.

"We just got through the big drought and could see the rain coming, we were all very excited," Mr Foyster said.

"So we stopped watering the orchard the day before the anticipated rain, but unfortunately it came in the form of hail."

It had been so dry at the orchard that they had to truck in water daily for three months to keep the trees alive and growing.

"There's no readily available water close to our farm, we're at the top of a plateau, so I set up a semitrailer with bulk tanks and went and canvassed all the local farmers, cattlemen, anyone that had an excess water supply, a small dam," he said.

The hail stones also snapped off and scarred branches of the avocado trees at Pretty Gully. ( ABC Rural: Kim Honan )

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"I pumped that onto the back of a truck and hauled between 100,000 and 150,000 litres per day to supplement the water that I had to get through that dry period into the cooler growing time.

"The roads here aren't up to standard. I went through a set of tyres every three tanks of fuel just shredding them on the hard rock coming up the mountain."

Then came the destructive bush fire near Tabulam that destroyed more than 20 homes and burnt out more than 4,000 hectares.

Mr Foyster said they were lucky that the orchard did not go up in flames.

"It only needed a good southerly wind and it would've been here within a 24-hour period. As the crow flies the fire was probably about 7 or 8km from the orchard," he said.

"We did a lot of preparation around the orchard with fire breaks and set up a lot of our own equipment in preparation for it.

"The one thing about the fire is that we were aware of it for four or five days, so we had a little bit of a chance to prepare for it and thankfully for us it didn't eventuate."