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Development of IPM strategies for management of slugs on Christmas trees

Slugs are an understudied pest of Christmas trees in Oregon and Washington despite being one of the most importance relative to load rejections in Mexico, Japan, Hawaii and other Pacific Rim destinations. For example, when a shipment of trees contaminated with Arion slugs is discovered in Hawaii which has zero slug tolerance officials reject the load, and either ship it back to the Pacific Northwest or have it cleaned up in Hawaii at the shipper’s expense. Current strategies for managing slugs (e.g. shaking) are unreliable and consequently slugs continue to pose a significant economic problem for Christmas tree growers in the Pacific Northwest. Thus, in order to develop effective tools for managing any pest it is critical to know what species are infesting the target crop and surprisingly this information is currently lacking for slugs in Christmas trees. This knowledge gap makes it very difficult to design effective approaches for their management. Our results show that eight different slug species infest Douglas fir plantation in Oregon and Washington. Of these, A. circumscriptus, A. subfuscus, A. rufus, D. laeve, D. reticulatum, and L. maximus are European invasive species (Mc Donnell et al., 2009). The remaining two species, A. columbianus, and Prophysaon sp. are native to the Pacific Northwest and are generally not regarded as pests. These native taxa are forest dwelling species and thus their presence in Christmas tree plantations is not surprising. Of the eight species that we collected during our surveys, D. reticulatum was the most abundant, and accounted for ~70% of the total catch in plantations and yards in both Oregon and Washington. However, given that this species is a widespread global pest and has been recorded in Hawaii and throughout the Pacific Rim, it is not regarded as a quarantine species. On the other hand, the presence of A. circumscriptus, A. rufus and A. subfuscus in a shipment of Christmas trees would lead to shipment rejection at ports of entry and importantly these species were present in both holding yards and plantations in the Pacific Northwest. Thus, effective management of these species should be a priority for growers. Our laboratory baiting trials showed that a number of commercial and widely available molluscicides caused high mortality to A. circumscriptus and these baits should be used as part of an IPM approach for management of the species. Bait should be broadcast in areas favorable for slugs (e.g. edges of yards, areas of debris, patches of weeds). Furthermore baits should be applied at times when slugs are active and likely to encounter and consume a pellet (e.g. when a spell of rain is followed by dry weather; temperature >50°C). Broadcasting baits during consistent wet weather is not recommended as such conditions result in rapid breakdown of the pellet and reduced efficacy. Spring and Fall applications will also be more effective than Summer and Winter applications. Although our laboratory bait trials were more limited with A. rufus and A. subfuscus, these slug species may be more difficult to manage with baits alone and consequently other tools will likely need to be employed including shaking, weed removal, debris and trash removal, and avoiding leaving harvested trees on the ground particularly overnight.

  • Project ID16-03-OSU
  • CategoriesPost Harvest
  • Growing Region(s)Pacific Northwest
  • Tree SpeciesDouglas-Fir
  • Investigator(s)Mc Donnell, Landgren, Chastagner
  • Institution(s)Oregon State University, Washington State University
  • Research Year2016
  • Publication Year2020
  • ReportDownload 📁
  • URL(s)