Destruction of Sod-seeded Legume Seedlings by the Snail (Polygyra cereolus

Florida's perennial forage grasses, dormant during winter and early spring, provide little new forage unless overseeded with a cool-season crop such as clover (Trifolium spp.) or alfalfa (Medicago saliva L.). Sod-seeding legumes in bahiagrass (Paspalum notatum Flügge) has resulted in poor establishment unless areas were desiccated with 0.28 kg/ha of paraquat and burned 48 hours later. Poor stands were believed to be due to seedling loss by the snail (Polygyra cereolus Muhlfeld). These experiments were designed to test this hypothesis and determine if burning killed snails. Five experiments were conducted. 1) Populations were estimated by counting snails in 0.3m³ areas and by tallying snails in traps. 2) To determine legume mortality rate, 0, 1, 3, 5, and 7 snails were placed in enclosures with 20 white clover (T. repens L.) seedlings. 3) In a similar experiment two or four snails were exposed to 40 white clover seedlings drilled in rows. 4) Alfalfa, red (T. pratense L.) and white clover were exposed to snails to determine differences in legume susceptibility. 5) Finally, the temperature was recorded 2.5 cm above, 2.5 cm below, and at soil surface during the burning of bahiagrass. Snails were placed on the soil before the burn and their mortality was determined. During a 44-day trapping period in newly seeded legume plots there was an average total of 13.6 snails found vs. 14.0 snails in unseeded bahiagrass. The number of snails per 03m3 was 0.9 vs. 0.84 snails in the respective areas. Greenhouse studies indicated that P. cereolus was responsible for legume mortality. White clover was more susceptible to loss than red clover or alfalfa. More than one snail per 20 seedlings constituted a threat to legume establishment particularly when added to losses from other causes. Burning bahiagrass after desiccation with paraquat resulted in 98% mortality of P. ceveolus. Temperatures at the soil surface rose from 27 to 83 C in 75 sec then dropped to 37 C after 5 min.