Updated February 14, 2023:
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It has been suggested by other researchers that slug eggs hatch in fairly defined periods of time. Baits applied at slug egg hatch would be the most effective at reducing populations. Further, soybean planted before egg hatch might avoid significant damage. The goal of this project was to determine if there was a degree day target that could predict when slug eggs hatch. Nine fields each in 2020, 2021, and 2022 were sampled using shingle traps and residue sifting to find neonate slugs. A subset of slugs in 2020 and 2021 were held in the laboratory to determine if any were infected with potentially pathogenic nematodes. Before departing UD, Dr. Ivan Hiltpold discovered a nematode infecting slugs and was responsible for almost 10% slug mortality. This effort expanded on his work.
Early on in the project, it became clear that our two primary species, gray garden slug and marsh slug, have different life stage timing. Marsh slug neonates were observed in some fields at the beginning of the sampling periods in early March, suggesting that marsh slug eggs can begin to hatch in late February and early March. In some fields, peak egg hatch did not occur for a period of time, and peak populations occurred several weeks later. Gray garden slug eggs on the other hand appeared to have somewhat more defined hatching periods. Fewer fields were identified with neonate gray garden slug. In 2020, egg hatch occurred the last week of March to the middle of April. In 2021, it occurred at the end of March, but in 2022, egg hatch occurred in early March up until the first week of April.
In Fall 2020, 269 slugs were collected for nematode observation. 83 slugs were infested with nematodes, although they were not killed quickly by them. There appeared to be two different species of nematodes infecting slugs. In the Spring, 242 slugs were collected from 9 fields. 47 of the 214 marsh slugs had nematodes in them, while none of the gray garden slugs collected in the Spring had nematodes.