Keep on trapping
As December begins, half of the Slugwatch sites across the arable area of England are showing high numbers. Most have a high proportion of juveniles so later drillings and less advanced crops still need monitoring.
There is a mix of species present at most sites and ADAS entomologist David Green reports that his site in Shropshire is no exception. "We've got round-backed slugs as well as field slugs and a few keeled slugs too. The majority of the population, about 60%, is coming out as the field slug at the moment, both adults and juveniles.
"Juveniles can cause damage as well as adults, particularly the more important damage for wheat, feeding on embryos of wheat grains causing grain hollowing and later on shredding of foliage. So both large and small slugs are important.
"We're getting dusky slugs in appreciable numbers on some sampling occasions. Arion are potentially capable of causing damage as well. Usually the smaller species tend to be more important than the larger Arions."
Summing up the national picture from Slugwatch, Bayer agronomist Gareth Bubb says half of the sites are showing high numbers of 30+ per square metre and 55% of these are juveniles less than 1cm in length. The species split reflects the Shropshire site with a national average of 60% grey field slugs and appreciable numbers of Arions.
"Cereal crops into mid-tillering should hopefully be past the damage stage, but later drilled cereal crops, that are prior to tillering or at early tillering, still need to be monitored", he advises, "Where monitoring indicates a need to treat methiocarb will give equal activity over the range of species and considering the cooler winter weather, you need a pellet like methiocarb that works equally as well irrespective of temperature."
David Green adds that it's important to keep on checking into winter: "even though we've had some frosty conditions in late November, which considerably reduced slug activity, we know from other work that slugs are probably still there in the soil. And with the return of warmer weather and slower crop growth, as a result of the colder soils, growers still need to keep a check on things, particularly if oilseed rape crops lose leaves during the winter.
"It's worth adding that when checking for slugs with refuge trapping you need to do so under conditions suitable for slug activity, essentially when the soil is wet. Trapping under unsuitably dry conditions you may end up with a low or zero catch but that doesn't necessarily mean a low risk to the crop.
"Numbers in the soil can vary with conditions. We know from last year that sampling in dry conditions can apparently depress slug populations as can sampling in cold weather. We've also seen that numbers can quickly rebound given suitable weather conditions."
To keep a watch on slug numbers in their area growers can view Slugwatch free-of-charge online at www.bayercropscience.co.uk and download the latest 'Four Seasons LIVE' podcast to hear more about Slugwatch.
