MODIFYING the harvester gives farmers a last chance to control snails and prevent them from entering the grain sample.
Early results from trials in South Australia have shown that using the right design of dislodger bar is effective at reducing the number of snails entering the header.
Rigid snail dislodger bars attached to the front of the reel have performed best in reducing snail contamination in standing cereal crops (see photo). In faba beans, a bar fitted with dangling V-belts was the most effective in reducing the number of snails and minimising crop loss (see photo).
The dislodger bars aim to flick snails off the crop and onto the ground so they do not contaminate the grain, resulting in downgrading at the silo. However, the trials found that any reduction in grain contamination achieved through modifying harvester machinery is likely to be at the cost of significant yield losses.
Yorke Peninsula trials
The trials were conducted on Yorke Peninsula during the last harvest, supported by farmers and the Federal Government through the GRDC, involving a number of farmers, manufacturers and local industries.
They were the first in a three-year research program being conducted by the Southern Yorke Peninsula Alkaline Soils Group, project managed by Michael Richards, in conjunction with UniSA's Agricultural Machinery Research and Design Centre.
The trial results should encourage crop producers to invest more on earlier, adequate snail control strategies, according to Jack Desbiolles of UniSA's Agricultural Machinery Research and Design Centre, who helped coordinate the research.
"Harvester modifications should be regarded as the last option when all else fails," Dr Desbiolles said.
Last resort options
According to trials in barley and faba beans, matching the dislodger bar design to the crop type is essential to get rid of the most snails while minimising crop losses. A crop's susceptibility to mechanical losses was the key factor in determining the type of dislodger bar used.
For standing cereal crops, a rigid pusher bar set close to the cutting height performed best in the first year trials. "It dislodged 50-70 per cent of round snails from the harvest zone· and yield losses were only 2- 3 per cent," Dr Desbiolles said. "However, losses easily double when travelling against the hook in barley crops."
A steel Duragal Rail profile (120 x 48 mm) and a PVC pipe (125 mm diameter) both performed well as pusher bars in the trials in cereal crops. Other dislodger bars trialed in standing barley included dangling chains and V-belts.
"While they both caused low yield losses of less than 0.5 per cent, they also removed only 10- 20 per cent of the snails," Dr Desbiolles said.
"Polypropylene brushes, which performed above average in cereals and showed the potential to cause proportionally lower yield losses than rigid pusher bars, were also trialed. However, their performance varies with crop density as the brushes become comparatively more rigid when operating in thinner crops. More evaluation is planned for next season.
"Other dislodgement devices trialed were thick rubber curtains or water-loaded inflatable airbags which created a gradual wiping action on the crop.
"While they achieved no yield losses in cereals, they dislodged very few snails, lacking aggressiveness in their action." In faba beans, dangling V-belts with a 100 mm spacing performed best, dislodging 35-60 per cent of round snails from the harvest zone and causing yield losses of only 4-5 per cent.
Using heavy dangling chains set at 50 mm spacing removed up to 85 per cent of round snails from faba beans but caused at least a 7 per cent yield loss. That loss is likely to be in addition to typical front reel losses at harvest of 10- 15 per cent.
The rubber curtain or inflatable airbag devices are not suitable for harvesting faba beans.
"Apart from the design and setting of the snail dislodger bars, other factors that affect their effectiveness are crop conditions, the header speed and snail type and density," Dr Desbiolles said. The barley crops in which the dislodger devices were trialed had a plant density of 280-400 ears per square metre and a snail density within the harvest zone of 25- 110 medium to large rounds per square metre.
The faba bean crops used in the trials had a plant density of 17-23 per square metre and a snail density of 110- 120 large round snails per square metre.
Conical snails, which are much harder to dislodge than round snails, were also present, but their density was difficult to assess. Dislodger bars were found to be one to three times less effective on conical snails, being most effective with larger round snails located higher up the canopy.
The dislodger bar designs were tested on a dual operator- held frame and a 1420 Axial Flow International Harvester. Further research will be conducted over the next two years and this will include more work on dislodger bars and a stripper header front.
Initial results for snail removal with the stripper front over the conventional open front and pusher bar set-up were excellent for reduced snail intake and reduced snail contamination in the grain box at similar grain losses. At the same time, work rates were increased by 25 per cent.
The results of the trials of dislodger bars and other techniques to minimise snail contamination are outlined in an advice sheet, Harvest Techniques to Minimise Snail Contamination, which is available on the GRDC web site - www.grdc.com.au/bookshop/free.htm.
Program 2.7.1 Contact: Mr Michael Richards 0427 547 052 Email RichardsM@bigpond.com.au