Controlling rats in macadamia orchards used to be very tricky. Infestations are generally quite hard to detect until they have already caused significant damage and loss.

You might spot broken twigs or branches that indicate roof rats have built nests in the tree canopy, well-hidden because of the dense foliage, says Mark Wilson, BASF’s technical services manager.

Another sign is gnawing on the irrigation pipes as thirsty rats have been looking for water. Either way, the rats have been in the orchard for a while.

Mr Wilson said finding out that rats have already moved in is a major cause for concern. “They can destroy a significant percentage of the very valuable crop you’ve invested so much money in producing. Controlling rodent populations is always much easier if you can catch the problem early and deal with low numbers.

“The other big challenge until a couple of years ago was that even once you knew you had a problem, there were no rodenticides registered for use in macadamia crops.

“Products were – and in many cases still are – chosen on the grounds that there’s nothing on the label that says they can’t be used in macadamia orchards. By the same token, there’s nothing to say they should be.

“In practice, most of them are quite unsuitable. The control they provide in the orchard environment can be unreliable and inefficient and put beneficial predators like raptors and owls at risk.

“Selontra Soft Bait rodenticide from BASF is very different. It has the ideal profile for very effective, sustainable control with minimal risk to other wildlife. That’s why it became the first rodent bait specifically registered for use in macadamias in 2020.”

Mr Wilson said Selontra can quickly bring existing infestations under control. “Plenty of growers who have used it to turn around dire situations can vouch for that – but the best way is to use it preventively.

“Because monitoring rodents in the crop is so difficult, the best way to prevent rodent damage is by setting baits that the pests will find even more attractive than the crops.

“Selontra has a proven ability to attract rats, no matter what alternative food sources are on offer. You just have to make sure it’s placed in areas that they’ll pass by.”

Mr Wilson said when Northmac took over an established but run-down 34,000-tree macadamia orchard at Oakenden near Mackay, they had to begin by cleaning up a very large, well-entrenched rat population. They tried a range of baits and quickly identified that Selontra was the most attractive and effective.

“Selontra’s ability to quickly establish and maintain control of rodents is complemented by another, even more important advantage over alternative treatments: minimal risk of secondary poisoning.

Secondary poisoning is the accidental poisoning of non-target animals that feed on the dead bodies of pests that have ingested a bait.

Standard rodenticides are classified as anti-coagulants. They thin the blood to cause massive, fatal internal bleeding.

“It’s generally pretty effective, but the big drawback is that the active ingredient lingers in the carcases and remains potent. So, if an owl or a hawk – or your pet dog – eats a rat killed by a standard product, they will receive a dose of the poison.

“Even if that dose isn’t fatal, they can add to it by eating more carcases and the poison will keep building up in their systems.

“Again, Selontra is very different,” Mr Wilson said. “It’s quickly metabolised by mice and rats, then breaks down quickly in the environment after they die. So, there is very little chance of a predator consuming a lethal dose.”

Mr Wilson said there’s one more advantage that helps convince growers Selontra is their best option.

“If you’re setting out baits to maintain control, you don’t necessarily want to have to check and refill the bait stations too often. It’s time-consuming and the costs add up.

“Even a single rat can eat a lot of any standard bait, because they can keep eating their fill for days while it’s slowly taking effect. That might be many times a lethal dose, which makes their carcases more deadly to other animals and means a lot of product is wasted.

“Using Selontra is far more efficient because its ‘stop-feed’ technology causes rodents to lose their appetite after consuming a lethal dose. That reduces wastage, lowers costs and means a single bait block can last much longer and control many more rodents.

“It’s just a final clincher that makes Selontra a great match for macadamia growers’ needs.”