14 September 2001

Specialists back PC traps

Over the following three pages

our Pest Control Special

helps you combat grain

storage pests, rabbits and

slugs. Here Amanda Dunn

takes a closer look at the

use of PC traps to monitor

stored grain for insect pests,

a practice that could become

compusory under assurance

schemes rules next year.

Edited by Charles Abel

MONITORING grain stores for insect pests is notoriously difficult, so can PC traps really bring benefits and if so how should they be used?

Most storage specialists support their use, stressing that they are significantly more effective than alternative approaches.

"Finding insects in any form of bulk grain storage is very difficult," says Achetas Mike Kelly. "We know that conventional methods such as sampling and sieving are extremely inefficient and they are recognised as such.

His comments are echoed by CSLs pest management scientific liaison manager Paul Cogan. "Conventionally sampling grain using spears is a very poor way of detecting insects. By the time you see pests they are at a high level and damage will already have been done."

Ten years ago, with the aid of HGCA funding, Mr Cogan developed the PC trap, a system proven to be 10 times more efficient than conventional methods.

"We looked into various traps that could be used, knowing that UK grain needs to be monitored for insects that spend most of their time on the surface, such as the grain weevil, as well as other species that congregate below the surface, such as the saw-toothed grain beetle and the rust-red grain beetle."

PC traps should be placed in pairs, one on the surface and one just below, in a 4-5m grid formation, as soon as possible after grain enters the store.

In silos where health and safety prevents extensive access, two traps should be placed at the silo entrance, one on the surface and if possible, one just below.

"If silos have a side which is sunnier, provided it is safe, place traps on the warmer side which is likely to attract more activity," advises Mr Kelly.

"While grain is warm, pests are likely to be most active," says Igroxs Ian Clayton-Bailey. "Traps should be laid down as soon as grain goes into store and monitored at least weekly. Once temperature drops below 10C and the commodity becomes more stable, fortnightly or even monthly checks will suffice."

Monitoring should involve tapping out contents of traps on to a tray with a white background and recording any findings together with the decision made.

"Do not be shy about recording decisions," advises Mr Kelly. "At 10-12C if a farmer finds a single grain weevil and decides not to do anything he can still write down why he has made that decision."

Mr Clayton-Bailey agrees. "Detection of pests does not mean automatic treatment. Identification and risk assessment should be pre-cursors to any treatment.

"Use the trap as a monitoring tool," Mr Clayton-Bailey continues. "If on first inspection three pests are found, record this and then go back in 4-5 days time. If numbers are higher this may suggest the problem is getting away from you and treatment may be appropriate. But if numbers start to reduce while cooling grain, this suggests you may be in control of the situation and a risk assessment should be carried out before deciding whether treatment is necessary."

As a rule of thumb, if there are six or more insects in 25% of traps, stored grain may be getting to the point where treatment should be considered, confirms Mr Cogan.

Cooling alone may be sufficient to kill off pests, as little or no activity is likely below 10C.

PEST PRESSURE

Potential monthly pest

increase

&#8226 Saw-toothed grain beetle – 60x @ 35C.

&#8226 Rust red grain beetle – 60x @ 38C.

&#8226 Grain weevil – 15x @ 28-30C.

Source: Acheta.

Treatment costs

&#8226 £1-£3.50/t curative fumigation – three month guarantee.

&#8226 75p-80p/t chemical + handling – no guarantee.

Source: Igrox.

PC TRAPS

&#8226 Place in grain ASAP.

&#8226 Position in pairs – one on surface, one below (max 10cm depth).

&#8226 Arrange in 5-6m grid formation.

&#8226 Check weekly until grain cools to 10C, then fortnightly/monthly.

&#8226 Tap contents on to tray with white background.

&#8226 Identify pests.

&#8226 Record findings and decisions made.