Effects of simulated rainfall on two contrasting metaldehyde slug baits.

Slug pests can cause considerable damage to horticultural, pastoral and arable crops, particularly at crop establishment. There is a competitive market for slug baits, most of which use the active ingredient metaldehyde. However, for this single active ingredient there are many products of contrasting formulations, pellet sizes and application rates. While there is anecdotal evidence that some commercial products break down under heavy rainfall, this has not been confirmed experimentally. The efficacy of high and low rates of two contrasting commercial slug baits (large vs. small pellets) was compared under high and low simulated rainfall regimes. Plots were shielded from natural rain such that simulated rainfall could be controlled. The baits were assessed for their ability to protect forage brassicas from slug damage, and both plant establishment and slug grazing damage were recorded. The two baits performed differently under the differing rainfall regime experiments. In the low rainfall experiment carried out at the beginning of summer there was little slug damage, all baits significantly reduced slug damage but there were no significant differences among bait treatments. In the high rainfall experiment carried out at the end of summer there was considerably more slug damage, and the low rate of the small bait pellets did not significantly reduce slug damage, unlike the other three bait treatments.