New trap helps manage snails in irrigated rice fields

Santa Catarina's irrigated rice producers eagerly await September to begin planting the new crop, but it's also the time when pests tend to appear, attracted by the availability of food in the form of seeds. One pest that has worried rice farmers is the snail, which enters the fields through the ditches after the fields are flooded. But starting this year, producers have a powerful ally: the Schneckel trap, developed by the entomologist. Eduardo Hickel (in the photo), from the Itajaí Experimental Station (EEI), which is in the dissemination phase through Epagri extension agents.

The trap was developed by the researcher in 2024, after three years of testing. Until then, only submerged traps were available to capture mollusks, but the three species identified by Eduardo (large snail, flat snail, and small snail) need to come to the surface to breathe and would often escape the traps. The challenge was to devise a mechanism that would prevent the animals from escaping.

So, he developed a trap using a PVC pipe with an opening covered with a shade cloth, which allows water to enter upon installation. Snails enter the trap, attracted by a food bait (1g of food) through two openings in the pipe; plastic mesh funnels fixed inside prevent escape. The trap must be installed in a minimum depth of 30mm of water, with stakes placed around the pipe to prevent other animals from knocking the traps over.

The technology was presented to extension workers in July during Epagri's Rice Project meetings and could become an important tool for identifying the incidence of these animals, which can cause considerable crop losses and even require new planting. This is particularly true because these species cannot be controlled with pesticides, but require integrated management, which includes early preparation of dry soil, cleaning of ditches and canals, installing screens at the water intakes of the fields, maintaining water levels, and occasionally draining infested areas.

Other control methods include placing papaya, cassava, or banana leaves to collect snails and introducing predators such as snail kites (requiring perches) and Peking ducks, at a rate of 30 to 50 per hectare. Crop management during the off-season is also necessary, and, occasionally, alternating cultivation systems and adopting dry-soil sowing.

Monitoring in the experimental field is done three times a week

Although the technology is already in the dissemination phase, Eduardo's work isn't finished. In the second week of September, he began a new experiment at the ISS to monitor snail behavior throughout the harvest season, which ends in March with the harvest. "This isn't population monitoring, as the snails there don't grow rapidly in number. The large snail, which is quite voracious, lives up to three years, while the flat snail lives for one year," he explained.

To monitor this situation, Eduardo installed seven traps across a 15-hectare area: four in ditches and three in fields. The samples are read three times a week. At the same time, he is testing different combinations and quantities of food (fish feed, rabbit feed, etc.) in the laboratory to prevent snails from attacking the seeds. At the end of the harvest, the study will lead to recommendations for improving the control of these animals that have been keeping rice farmers awake at night.

The researcher explains that, in the case of commercial crops, producers are advised to monitor only until November, when the plants are still young and most susceptible to pest attacks. "In irrigated rice farming, there is no other food available for these animals other than the plant itself, so for more efficient control, integrated cultural, mechanical, and biological management is essential," he concludes.