2016 could be worse for slugs than 2012
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Growers are being urged to prepare for a slug onslaught this summer as reports indicate populations have surged after several months of wet weather and may even surpass that of 2012.
The spring months of April and May typically represent the peak in the slug breeding cycle and with regular showers during this time and since, molluscs have enjoyed excellent conditions.
With an already high population coming through the winter the pressure could be intense, says slug expert David Glen of Styloma Consulting.
“Newly drilled oilseed rape crops will be particularly susceptible and those intent on establishing crops early to overcome flea beetle attack should be wary of exchanging one pest for another,” he says.
Every opportunity to reduce numbers through cultural controls, such as straw raking, should be fully exploited to limit damage potential.
“Effective control begins with good stubble hygiene, such as destroying the green bridge between crops, but the pressure to establish the next crop can mean this is compromised, especially in wet weather,” he says.
Although not practiced in average years, where slug populations are particularly high and the stubble is moist, David Glen suggests making applying pellets to stubbles in the days after combining, provided that the pellets can be left undisturbed for a few days before drilling.
“The move to direct drilling has all but removed the control benefits once derived from deep cultivations so tactics need to evolve in response. The threshold for applications is quite low in practice, just one slug per trap in stubble before oilseed rape and four slugs per trap ahead of a cereal, so an application of about 30 pellets per square metre shortly before drilling may be advisable.”
After drilling standard advice resumes and he is quick to point out the benefits of rolling in consolidating the seedbed.
“Rolling post-drilling is probably the single most worthwhile action a grower can make before applying pellets. It reduces the ability of slugs to reach vulnerable seeds and seedlings in the soil, deprives them of the living spaces to retreat to during the day and ensures pellets are not lost below the surface.”
Only after exploiting all practical cultural controls should growers consider pellets, says De Sangosse commercial manager Simon McMunn.
But pellet choice is critical he says and by utilising both types of active substance – metaldehyde and ferric phosphate – it is possible to achieve effective control over a prolonged period while managing application limits.
Metaldehyde and ferric phosphate pellets are equally effective, but the different modes of action mean that the effects of one are more readily obvious.
“Metaldehyde destroys the slug’s mucus producing cells rendering them immobile which is why they die on the surface. In contrast, ferric phosphate is a stomach poison which causes the pest to stop feeding immediately, but means it may have retreated underground before death occurs so its effects can seem less obvious.”
What sets pellet performance apart however, is size and manufacturing process.
“The pasta-based larger pellets such as TDS and Ironmax Pro are often the most effective as they have the mass needed to spread evenly and the durability to persist,” he says.