15 September 2000


baiting to waste rats

DONT rush to blame resistance for your failure to control rats. Thats the message from Martina Flynn, Sorex rodenticide product manager. Poor baiting practice is far more likely, she says.

"There is an impression that all anticoagulant rat baits are becoming largely ineffective. That is untrue.

"There are at least two perceived types of resistance – the original, first-generation warfarin resistance and the more recent tolerance to second-generation products, including difenacoum and bromadialone."

Although resistance to the newer materials undoubtedly exists on a few farms in Berks and Hants, the midlands and the north, the picture is much the same as it was 10 years ago, says Miss Flynn.

"The vast majority of suspected cases of resistance are due to operator error. It usually comes down to a lack of understanding about bait placement and the amounts needed for effective control. Ridding rats from some sites may need particular expertise."

Keeping the pests at bay is not easy and requires a methodical approach, she adds. Sorex recently issued a free guide to best practice.

"Are you using the correct active ingredient? Many rats are resistant to first-generation anticoagulants like warfarin and coumatetryl.

"Have you surveyed your area thoroughly to pinpoint where rats live, feed and move? Check for greasy runs along walls and in vegetation around buildings. Look for rat holes, especially near water. Check inside buildings for damage and droppings, and watch out for tracks in dust and mud.

"It is a good idea to plot what you find on a plan, so you can bait accordingly."

Different bait types suit different situations. A cut wheat loose grain base is cost-effective, blocks are particularly useful in burrows, and plastic sachets are best applied as barrier baits, usually towards the end of a control programme.

Where possible, restricting access to other food sources, removing spilt grain and putting lids on feed bins helps a lot. "Trying to get rats to eat baits when these are still around is difficult," says Miss Flynn.

"To avoid aversion to your bait points, leave the baits down for four to seven days and then clear all the other food sources away. Rats are wary of new objects and moving existing food sources makes them unfamiliar and less attractive than the baits."

Also, baiting may need to continue for longer than expected. Anticoagulants work slowly and a rat can take up to 10 days to die after ingesting a lethal dose, she says.

"You may need to wait two weeks before you see any signs that an infestation is declining. Rats usually die in their burrows.

"Ask yourself whether you have enough bait points. Not having sufficient is probably the most common reason for control failure. For every rat you see, there are probably 10 more unseen. Id suggest a minimum of five points for a small infestation. You may need 40 or more for a large one."

It is essential to replace eaten bait until no more is taken, says Miss Flynn. "Check every day for the first three or four and then once every three to four days. If it has all gone, increase the amount used.

"Sometimes you think you have overcome the problem, but rats seem to be coming back. If thats the case, check to see that you havent missed any outlying spots harbouring them and treat accordingly.

"Unfortunately, your neighbours may not use a complete control programme, and rats will soon invade the vacuum you have created. Set up semi-permanent barrier baits to protect your area from becoming reinfested. Monitor them every two to three weeks and restart you own programme if you see any signs of activity." &#42


&#8226 Survey problem in detail.

&#8226 Choose correct active ingredient.

&#8226 Use plenty of baiting points.

&#8226 Inspect and top up frequently.

&#8226 Set up barrier baiting stations.

Rodenticide resistance

Resistance to second-generation rat poisons does not appear to be spreading as quickly as resistance to warfarin did, says the CSLs Alan MacNicoll.

"There are a few hot spots around in north Berks and south Oxon, and we have found it in East Anglia and Humberside. Resistance to warfarin, which occurred around Welshpool in the 1960s, spread at about three miles a year. Resistance to bromadialone and difenacoum, first noticed in Berks in the 1970s, doesnt seem to be growing."

However, the most recent MAFF survey, in 1995-98, of 23 "ratty" farms across the country found 18 had resistance of some sort, says Mr MacNicoll. A new Rodenticide Resistance Action Group, comprising representatives from manufacturers, the pest control and farming industries and academics, had its first meeting last April. It aims to examine ways to tackle the problems of resistance specifically in the UK.

Rat attack – dont blame resistance for reduced control. Better baiting can work wonders.