Farmers must do more to control rats

That is the finding of the latest annual study, undertaken by Farmers Guardian with BASF Pest Control Solutions this winter.

The National Farm Rodent Control Survey, which has been conducted on the same basis each winter since 2007 has, until now, shown a steady improvement in key elements of farm rodent control practice.

However, latest results from around 100 farms spread over more than 40 counties of England, Wales, Scotland and Northern Ireland suggest a worrying reversal in this trend in the past 12 months (See figure 1).

The extent of this reversal is underlined by the fact that only 22 per cent of farms are currently employing four or more of the six key elements of best baiting practice against the 27 per cent in 2009 and 57 per cent are employing two or fewer elements, compared with 42 per cent in 2008.

“Our results show farms with arable and pig and poultry enterprises are clearly being more diligent in their rodent control than grazing livestock producers,” says study co-ordinator, Shirley Wilson of BASF. “But this isn’t because they are experiencing any greater level of threat.

Infestation levels

“Indeed, dairy units, in particular, are reporting notably higher levels of both rat and mouse infestations than average. While they, like farms overall, have seen fewer significant rat or mouse problems than in 2009, a far higher proportion of these are rated as major (see figure 2).

“More frequent, bigger infestations and longer baiting periods continue to be identified as the three most important farm rodent control challenges,” she says. “As a result, most producers undertook three or more cycles of rodenticide baiting last year, with six in every 10 baiting in six or more of the 12 months and nearly a quarter in nine or more.”

The 2010 study shows average farm bait consumption at 39kg/year - slightly up on 2009 - and varying from 15kg per farm for those baiting just twice a year to more than 60kg for those baiting six or more times.

Although the peak of baiting was, as in the past, from October through to February, a far higher proportion of farms now appear to be using rodenticides throughout the summer - 17 per cent baiting in both June and July, compared with 10 per cent in 2009.

Among rodenticide active ingredients, difenacoum remains the most popular, being employed by around double the number of farms using the next most popular active, bromadiolone.

More than two-thirds of users chose a wheat bait - two-thirds cut wheat, one-third whole wheat - while blocks are preferred by 16 per cent and pellets 10 per cent.

Ms Wilson says the fact an increasing number are failing to implement most key elements of best baiting practice is a big concern.

“Good rat and mouse control depends upon putting down plenty of baiting points covering all the main areas of rodent activity and keeping them well topped-up,” she says. “Effective rodent-proofing and regularly baiting at key times of the year are important.

“Yet only around a third of people are currently baiting following the survey to establish exactly where rodents are (figure 1). Equally, fewer than four in every 10 are putting down more than enough baiting points.

“Only just over half are topping them up at least every five days. Just 20 per cent are rodent proofing alternative sources of food and around 40 per cent are only baiting when infestations are obvious, so it’s clear why so many people are continuing to find farm rodent control so challenging.”

Low resistance

Despite the intense pressure less-than-ideal baiting practice is placing on rodenticides, the survey shows resistance to the most commonly used actives remaining at a very low level on farm.

As in previous years, the latest survey found most people rarely, if ever, encountered rodenticide- resistant rats or mice in the past year. Even among the minority who reported sometimes or often encountering resistance, a good half did not report its classic symptom - poor control, despite good bait consumption.

“Under these circumstances, most current control problems almost certainly appear to arise more from insufficient rigor in baiting than from physiological resistance,” Ms Wilson stresses.

“Our farm studies show just how easy it is to think you have resistance just because you see a lot of bait disappearing, but still have rodent problems.

“Unless you bait widely and intensively enough, you will merely draw-in rats and mice from surrounding areas to replace those which succumb to the bait and crawl away to die. If you continue seeing rodent activity, assume the bait isn’t working.

“Time is clearly the enemy for many people here. You can’t put bait down where the rodents are if you haven’t surveyed the farm to see where the activity is taking place. Nor can you expect to control large populations if you fail to ensure your baiting points are adequately topped-up - especially so during the first week of treatment.

“Do the rodent control job right in the first place and it will pay you dividends, saving time and hassle, not to mention considerable damage.”

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