Background
The change in farming practice from tillage to minimum to no-till in combination with increased lime applications in the southern high rainfall agricultural zone has created favourable conditions allowing conical snail (Prietrocella barbara) populations to build-up (McDonald, 2018). Snails not only feed on germinated crops but contaminate harvested grain which may cause downgraded or even undeliverable loads (Smith, 2019). While there are a number of management options there is no silver bullet solution for controlling snails.
A number of products have been anecdotally suggested to repel snails and therefore have been applied as a foliar application as a means of reducing the number of snails contaminating grain. This trial was set up in a laboratory to test the repellence claims of these products, if conical snails react to the products and how long any effects on small conical snails last.
Aims
The aim of this trial was to test the snail repellence of products being promoted to repel snails in broad acre crops without supporting data or being registered for this use in crops.
Method
The treatments in these two trials were water (control), pyroligneous acid, saponins, urea (dissolved) and carbendazim.
Repellence trial
The five different treatments were sprayed onto standing senesced barley plants that were set in moist sand in pots using a spray boom to simulate an infield application. Individual pots had copper tape around the inside at the top to deter snails from escaping from the pot. The pots were sprayed then placed in a laboratory where 25 snails were added to each pot. The treatments were replicated four times and randomised within the replicates. Photos were taken of the pots every 3 minutes to monitor the movement of snails over time. The photos were edited into a time lapse movie and scored for activity. The maximum height of snails on stubble and the total number of snails on the stubble were measured twice a day for the first 3 days than at 15 and 21 days after application (DAA).
Snail mortality trial
In addition to the repellence trial we also tested mortality from exposure to the products. The spray was applied with the sprayer at the same time as the repellence trial mentioned previously with 20 snails in each pot. The pots were then randomised within the four replicates and placed in the lab and covered with mesh to stop snails escaping. To assess mortality at 21 DAA the snails were removed from the soil pots and placed in the centre of moistened paper in petri dishes. After one day snails which moved from the centre were counted as alive and those that didn’t were counted as dead.
Results and discussion
A spray application of all products tested in this trial as a way of repelling snails off the senesced barley plants proved ineffective.
Saponins reduced the proportion of time the snails were active over the first 24 hour period compared to the other treatments (Figure 1). The maximum height of snails on the stubble was also statistically lower for the saponin treatment than the nil and all other treatments (Figure 2). However the number of snails on the stem was not significantly different to any other treatments at any assessment timing (Figure 3).
Pyroligneous acid did not significantly reduce the total number of snails on the stubble or the maximum snail height on the stubble (Figure 2 and 3). However the activity of snails sprayed with pyroligneous acid was less than Nil in the first 24 hours post application (Figure 1). This experiment showed no evidence that this product repels snails.
Carbendazim did not prevent snails from moving onto the stubble and there was no significant difference in the number of snails on stubble between water treatment and carbendazim at any assessment time (Figure 3). There was no initial difference in the maximum height of snails between carbendazim and nil however the later assessments from 13 DAA onwards show the snails being located lower on the stubble below approximately 20cm from the base whereas on the nil treatments the highest snail was at approximately 36cm (Figure 2).
Urea had no effect on snail activity however it did appear to reduce activity over the first 24 hours similar to all of the other treatments when compared to the nil (Figure 1). Therefore the application of urea throughout the year most likely has no effect on the small conical snail populations on the crop.
At 21 DAA there was no difference in the number of snails on the plants between treatments (Figure 4).
In a 2019 field trial in the Esperance port zone, conducted by King Yin Lui (DPIRD) and Rachel Minett (Primaries), the effect on small conical snails of pyroligneous acid (500mL/ha) when combined with glyphosate was compared to glyphosate alone at swathing. At seven days after application it was observed that there was no significant repellence of snails by the pyroligneous acid and glyphosate treatment when compared to glyphosate alone. There was also no significant difference between treatments in terms of mortality rates seven days after application both in the field and in the laboratory. The grower did not report a decrease in the number of snails found in harvested grain samples from crop treated with pyroligneous acid applied under the swather bar.
Conclusion
No foliar spray treatments applied in this trial were found to effectively repel snails from senesced barley plants at any time during a three week period.
Use existing management techniques such as timely baiting as one of the management tools for controlling snails. Products should only be used at registered rates, times and methods of application in crops for which they are registered.
References
McDonald, D. K. (2018). Snail Management Guide for WA Farmers. Stirlings to Coast Farmers supported by Council of Grain Grower Organisation Limited.
Smith, D. A. (2019). Mitigating Snails, Slugs and Slaters in Southern Western Australia. Grains Research and Development Corporation.
Acknowledgments
Svetlana Micic, King Yin Lui, John Moore, Carlos Babativa Rodriguez and Jeremy Lemon.
This work was supported by DPIRD and GRDC within the 'Building crop protection and crop production agronomy research and development capacity in regional Western Australia' project DAW00256.