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Slugs

Agronomist, Sarah Heazlewood (Gorst Rural Supplies) has reported very high numbers of slugs in several cereal crops around Lake Bolac, Caramut, Streatham and Willaura, in the Western district of Victoria. Sarah says the slugs are quite small (less than 1cm in length) and can be found in wheat, barley and oat crops. Slugs have also been reported in other canola crops in the Western district in recent weeks. Although slugs mainly feed at night, Sarah has had no trouble finding slugs during the day when conditions are wet. There is some feeding damage along the tillers, although this appears somewhat different to typical slug damage caused by adults. Slugs eat by rasping plant tissue, using their specialised mouthparts. Researcher, Michael Nash (cesar), says feeding by smaller slugs generally appears as shallow rasped strips along leaves.

Slugs are unlikely to cause significant damage to cereal crops at this time of year, so baiting is unlikely to be cost-effective. Cereals are most susceptible at or soon after crop emergence. Because slugs are more likely to be found in paddocks where they have previously been a problem, it is advisable to record paddocks containing high slug numbers. Next year, these paddocks should be checked prior to sowing or before crop emergence. Using terracotta tiles, or another type of ‘refuge trap’ such as carpet squares or flowerpot bases is the best way to monitor. Traps should be placed on the soil surface when it is visibly wet, and then checked after a few days for the presence of slugs underneath.

Michael says the extent of slug problems next season can be related to current population levels, however there are two other important factors to consider. Higher moisture levels, thus availability of refuges, will assist adult survival over summer and will also determine the timing of slug emergence in autumn. Secondly, the availability of food sources, such as crop volunteers and weeds, is likely to have a significant influence on slug survival following their emergence.

Management strategies that can be useful in reducing slug problems are good crop hygiene, cultivation, and the removal of stubble. Sowing crops early is another strategy that will generally reduce damage. Consideration should also be given to planting less susceptible crops in paddocks with high slug numbers. Broadleaf plants such as canola and clovers are most at risk.

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