As slug populations lie in wait below ground following a dry spring, Geoffrey Bastard regional technical specialist at Certis, gives us his advice for getting ahead of the slimy army next season.
“Following a wet winter where slug populations built up considerably, we’ve experienced dry spells, which have caused slugs to retreat underground,” he says.
“However, as soon as it rains, the pest will emerge,” he says. “Over recent weeks I’ve witnessed slugs on flag leaves and ears. Although they will do little damage, this offers us a first look at what the population levels might be like in the autumn.”
Geoffrey stresses that being aware of the pressure you may face will be critical, as well as being prepared to act accordingly to stay on top of the pest this autumn.
Before the season kicks off, it is vital to build a complete picture of the field-by-field risk, says Geoffrey.
“Now is the perfect time to walk through crops to establish pest pressure.
“After it has rained, slugs will emerge from the ground to feed and will disperse throughout the canopy. Walk your crops during wet weather over the next few weeks to get an accurate picture of current pest numbers,” he says.
After harvest and before cultivation, Geoffrey highlights the importance of trapping slugs before further action is taken.
“After rainfall place nine slug traps in a ‘W’ formation, for fields larger than 20 hectares use 13 traps, leave overnight and examine early in the morning while the soil surface is still moist. If four or more slugs are found in cereal crops, then ferric phosphate slug pellets should be applied.”
“With straw prices being high, many will be looking to bale straw after harvest to help their bottom line, which will help reduce slug breeding areas,” he says.
However, those looking to chop and incorporate straw to increase organic matter will run the risk of increasing slug pressure.
“If crop residues are left in swaths on the soil surface, it can create the perfect breeding ground for slugs,” he says.
“Make sure that straw is chopped thoroughly and incorporated well to ensure this breeding ground is eliminated.”
Cultivation and soils
Water logged, and poorly drained soil can increase slug pressure, adds Geoffrey.
“Be aware of which fields are at highest risk and monitor these closely. Pay attention to fields with poor drainage, typically with heavy soil and a cloddy appearance.
“After harvest check all existing drainage to ensure it’s free-flowing. If you’re aware of areas of standing water in the winter, take steps to address these.
“The timing of cultivations is crucial,” explains Geoffrey. “Start only when optimum soil moisture levels are reached so that you don’t create a rough cloddy seedbed where slugs will thrive.
“Seedbeds should be consolidated and enable a good seed-to-soil contact to achieve robust and quick germination. A good soil structure not only reduces slug movement but can help crops grow away from the pest,” he adds.
Slug pellets are an important part of an integrated pest management (IPM) approach to slug control, says Geoffrey.
“With uncertainty around the future of metaldehyde, some growers are now switching to ferric phosphate for the flexibility it offers.”
Geoffrey highlights the importance of understanding the difference in slug behaviour when using a ferric phosphate based pellet, such as Sluxx HP.
“With metaldehyde, growers are used to seeing dead slugs and slime trails on the surface. However, ferric phosphate works differently. Recent research has shown that once slugs ingest ferric phosphate they retreat below ground to die.”
The study, conducted by Harper Adams University, showed that 50 to 60% of slugs who had ingested ferric phosphate pellets retreated below the soil surface, within the first 24 hours, and after two to three days, virtually every slug had died below the surface.
“Understanding slug behaviour and planning ahead, will be key to staying on top of the pest for the 2018/19 season,” he says.