Andrew Milligan farms in partnership with his brother James and their father Michael at Mains of Greenlaw Farm, outside Castle Douglas and has been owned by the family for 60 years.

In recent years, Andrew began sighting rats on the farm and involved local pest controller John Galloway, of South West Scotland Pest Control. “At first we saw the odd rat, but soon we were seeing dozens running through the fields towards our farm buildings. I brought John in because I had tried everything, but the numbers were still increasing,” said Mr Milligan.

Mr Galloway had been working with the Milligans on and off for almost 20 years. “Rat numbers need to be controlled in this area because there’s a river nearby, plenty of ditches and, when the fields are harvested and the temperatures drop, the rats look for places to find harbourage and breed,” he explained.

The infestation on the Milligans' farm had ballooned since last winter when Mr Galloway had finished his last treatment. “I only use rodenticides when I have to. Most of the time, rats can be kept away from buildings by other methods such as cutting away weeds, tidying rubbish, removing food and water sources and proofing buildings,” he pointed out.

Mains of Greenlaw extends to 250 acres and adjoins two further farms owned by the family. The land is mostly planted with cereals and there is some grazing for heifers.

“We have slatted sheds for the cows and this was where the main problem seemed to be. The rats were getting under the slats and breeding. You could see them running along the crust of the slurry and disappearing into holes beneath the slats,” said Mr Milligan.

This August whilst combining a field close to the farm buildings, Mr Milligan saw rats running away from the combine towards the buildings. “There were dozens and the following day I shone a light around the shed. There were eight cattle and about 40 or 50 rats, it was crawling,” he said.

The infestation had reached a level where he needed professional help and so Mr Galloway returned. In 2019, Mr Galloway suspected resistance to two rodenticide baits that he chose to use.

“I started with a bromadiolone bait and it had almost no effect. The rats were eating plenty of it, but there was no change in the bait take and I was finding very few dead rats,” he said. He changed to another bait with a different active, difenacoum.

“I started to recover some dead rats, but the bait take was still high which meant there were still rats feeding on the bait and I was not reaching a control point,” he added.

Rodents resistant to commonly used rodenticides are being identified in new areas of the UK and the increase in numbers of these so called ‘super rats’ presents a challenge to both farmers and pest controllers. Bromadiolone and difenacoum are the actives present in a number of common and widely available rodenticide baits.

However, these are proving ineffective against resistant rodents which are capable of eating large quantities of bait with no ill effects. “I had never experienced this before,” said Mr Galloway.

Following two treatments he was forced to use a third product, this time with the active brodifacoum. “It worked quickly and within weeks I was seeing very little bait take, which suggested that a level of control had been reached,” he said. However, the bait had only delayed the infestation and in 2020 when Mr Galloway returned at the end of August, the infestation was even larger.

Rats thrive when there is a plentiful supply of food, water, and shelter. A breeding pair is capable of creating an infestation of 2000 in just one year. Resistance had been compounded by using rodenticides without first establishing whether resistant rats are prevalent in the area.

“I suspected we were experiencing resistance, so it’s more important than ever that farmers and pest controllers establish whether there are resistant rats on the farm and choose the correct bait to control an infestation,” said Mr Galloway.

To treat the infestation Mr Galloway chose Storm Ultra Secure, a flocoumafen bait, manufactured by BASF. “Rats have no known resistance to flocoumafen and this new product is also more palatable because it contains a higher percentage of human grade food and no wax,” he explained.

Storm Ultra Secure is a single feed anticoagulant and the label required the product to be pulse baited. “Pulse baiting is an efficient use of a single feed bait because the first placements, or ‘pulses’, are designed to control the dominant rats that hunt for food,” said Mr Galloway.

He used bait boxes to secure the blocks of Storm Ultra Secure on wires. “I put 10 boxes down a week before I started baiting, to overcome the neophobic response rats have to new objects,” he added (rats have a fear of new objects, neophobia, so for a bait box to be effective the rat needs to have accepted the box as part of its environment).

“I checked the boxes after the first pulse on day three and almost all were empty, which was a good sign. I put more bait in and returned on day seven and the bait take had reduced,” he added, returning after 14 days to find very little bait take in the boxes and only one that was empty.

“I am happy that this has controlled the bulk of the infestation. I have removed dead bodies and topped up each box to control any remaining rats. The treatment has been fast and effective, so I will remove the bait in a week and continue to monitor the farm,” said Mr Galloway.

Mr Milligan cut away weeds, removed rubbish and made finding harbourage for any rat more difficult. “It’s important to be disciplined and reduce the ways that rats can find places to live and breed on the farm. We know that rats are in the fields, the ditches and down by the river but we just want to make sure that they are kept out of the buildings,” he said.

Rats continue to be a concern for farmers, but with the added complication of rodenticide resistance, farmers can only reduce the numbers by using baits that rodents have no known resistance to.

“There is a resistance map (see below) available online that farmers should consult before using any bait. If we work together to use baits that rodents are not resistant to, we can help to keep numbers under control,” concluded Mr Galloway.

* Rodent resistance maps can be found at:

If you suspect that you have resistant rats on your farm, these can be tested free of charge. All it requires is for you to cut the tail off three freshly trapped or shot rats and to pop in the post. Details can be found at