Abstract
Milbemectin, a mixture of natural compounds derived from the soil microorganism Streptomyces hygroscopicus subsp. aureolacrimosus, is a miticide/insecticide used for selective arthropod management. The objective of this study was to test spray applications of an emulsifiable milbemectin formulation (Ultiflora[tm] 1E) for phytotoxicity on a variety of ferns. Eighteen fern species representing 14 genera were treated just to the point of runoff with aqueous foliar sprays containing 0, 12 or 24 oz Ultiflora[tm]/100 gallons. Plants were held on raised benches in a double polyethylene-covered greenhouse with additional internal shading. Treatments were applied twice at 14-day intervals in two experiments. Acute phytotoxicity was determined visually for two weeks following each spray application and rated on a scale of 1 = no visible damage to 5 = death. In addition, fresh frond weights were determined 50 days after the initial treatment to assess chronic damage. For many species- Adiantum raddianum, Arachniodes simplicior, Athyrium nipponicum, Davallia trichomanoides, Dryopteris erythrosora, Osmunda cinnamonea, Pellaea rotundifolia, Platycerium bifurcatum, Polystichum tsus-sinense, Pteris cretica, P. vitatta and Rumohra adiantiformis -no damage was detected. For Didymochlaena truncatula and Nephrolepis spp., significant acute phytotoxicity was observed only at the 24 oz/100 gallons (2×) rate. Both Polypodium formosanum and Pteris quadriaurita were damaged at the 1 × rate. However, despite visual stunting of Nephrolepis biserrata 'Macho' at the 2 × rate, Ultiflora[tm] treatments had no effect on fresh frond weights of that fern or any others. Even though this was an EC formulation, Ultiflora[tm] applied at the 1 × rate did not cause significant damage to 16 of the 18 ferns used in this experiment.
