There is some concern that slugs will be as prevalent as last year, as populations have built up over last year. In addition there has been potential, with abundant summer rain, to give the slugs an early start to the season. This gives time for extra generations, as well as more green bridge for their feed source.
Our suggestion for growers this season is to check a few paddocks going into Canola, enabling them to monitor pest density and determine whether a proactive treatment protocol is warranted.
To determine the level of slug/snail pressure within the chosen paddocks a simple tile experiment can be used. Collect some 330mm square terracotta tiles from Kojonup Ag supplies and place them out in a known problem area of a paddock. It is also good to check an area you don’t think slugs will be an issue, as a control. One tile per Ha is adequate, if a minimum of 10 tiles are placed around an area to be monitored.
Each tile represents 1 square metre of ground. As the threshold for slugs in canola at seedling establishment is 1 per square metre, finding an average of 1 slug under each tile means your threshold has been met, and control is warranted.
One tip is to poke a 60cm long piece of wire in the ground next to the tile, with some high visibility tape tied to it, this means you can actually find the tile after placing it in the paddock.
Once the pest pressure has been established, the next question is what control measure is optimal. My preferred bait is SlugOut for high active ingredient loading, good spreadability and small bait size – this increases attraction to juvenile slugs. It also tolerates rain–it retains integrity even after 128mm rainfall as seen in figure 1.
|26mm||Coating on all baits
swollen. 100% intact.
|All baits swollen. 100% intact.
|All baits swollen. 100% intact.
|128mm||Coating on 18%
substantially dispersed, balance completely intact.
|6% broken down, remainder completely intact.
|18% partially disintegrated, 82% completely dispersed.
Figure 1: Comparisons of 3 different slug and snail baits.
Broadcast rates for SlugOut would be 2.5kg/Ha compared to Meta at 4kg/ha, to target bait density of 25baits per sq/m. This is the minimum number of baits per square metre for an individual feeding slug to have 80% chance of encountering bait on the first night.
Optimum set up for known problem area would be to spread post seeding with 2.5kg SlugOut, then watch baits – if consumed come back with Meta for cheap top up. Assuming rain is not an issue. Other options in known problem areas is putting 2kg with seed, and spreading surface baits post seeding.
Some farmers used rates that were too low last year and it cost them more, both in terms of re-seeding, and for top up spreading of baits. 1-1.5 kg is possibly not worth doing, as it won’t ensure control. Analysis of spreading 1kg of SlugOut is only equal to 9.4 baits/sq m, the chance of slug finding the bait is only 30%… threshold of 1 slug/sq m in canola…..if you need 3.3 nights to make 99% sure slug finds bait……then they have already severely damaged your crop establishment.
Kojonup Ag has SlugOut bait, Meta and an EDTA iron based bait in stock. We hire a slug bait thrower on a 1/2 or full day basis. For more information please call 98311022.