There is evidence of slug damage in many cereal and oilseed rape crops this autumn, according to Teagasc tillage advisors.
Wet weather is one of the primary factors; crops after oilseed rape and fields with a history of slug damage, have fared worse, according to latest analysis.
Tillage specialist, Ciaran Collins, said the fact that field conditions were not suitable for rolling has only increased the pressure on crops.
Collins added: “Slug grazing in oilseed rape is common but the main concern from now on will be winter wheat.
“Slugs often do most damage to winter wheat at the early stage by eating the endosperm resulting in the characteristic seed hollowing.
“Barley and oats are less susceptible at this stage due to their extra seed coat.”
Chopped straw may also be an additional factor as this will provide slugs with a source of food and land can take longer to dry out in a season like this year.
Slug traps
Where growers suspect slugs may be a problem the advice is to lay down some traps using a plastic bag or slate with muesli underneath to attract the slugs.
Traps should then be monitored on a daily basis to quantify the slug populations within a crop. If five or more are captured, treatment is warranted on emerging or struggling crops.
Slugs are most active at night so the best time to check slug traps is early in the morning.
Collins continued: “In a year like this, growers should not wait for the damage to occur; there is no harm in assessing the slug population before the crop is sown or immediately after sowing.”
The only cultural slug control option is rolling, if crop and ground conditions are suitable.
In relation to chemical control, this is largely based on products containing metaldehyde or ferric phosphate.
Growers are reminded that, as always, it is important to use the recommended rate on the label.
Applying reduced rates reduces the number of baiting points resulting in poorer control.
According to Teagasc, it is better to apply one full label rate rather than a reduced rate twice.
There are primarily three types of slug-related damage to be aware of:
- The shredding of the crop leaves;
- Poor emergence caused by hollowed-out seed;
- The appearance of yellow leaves, caused by slugs grazing below the soil surface.
“This last issue is a recently identified phenomenon, where slugs are concerned. The damage created is similar to that caused by yellow jackets,” Collins said.
But there are also additional risk factors where slugs are concerned, these include later-sown oilseed rape crops and oat straw that had been incorporated into the soil prior to the planting-out of a new crop.