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Alternatives to a pyrethroid for controlling madeira mealybug (Hemiptera: Pseudococcidae) on Coleus Cuttings

Abstract:

Mealybugs (Hemiptera: Pseudococcidae) are soft-bodied insects that infest a variety of ornamental plants, and early instars are almost undetectable to the human eye. Because the cryptic mealybugs can cause significant damage quickly, plant cuttings often are preventively dipped into pyrethroidbased insecticides. Dips differ widely, however, in their phytotoxicity, effectiveness in killing mealybugs, and operational efficiency and cost. Therefore, to assess the efficacy of alternative dips, tests were conducted on biorational products for controlling the Madeira mealybug, Phenacoccus madeirensis Green, on coleus plants, Plectranthus scutellarioides, var. 'Big Red Judy' L. (Lamiaceae). Initially, phytotoxicity was evaluated using different concentrations and exposure times for dips containing Natur'l oil, dish detergent, Wetcit®, or Vapor Gard®. The highest concentrations of these products for which phytotoxicity could be tolerated were 1%, 1%, 0.1%, and 0.1%, respectively, in 30 s dips. Based on the results, these concentrations were used in dips to evaluate their effectiveness in eliminating mealybugs. The most effective biorational product, Natur'l oil, then was compared with the commercial standard synthetic pyrethroid, Mavrik Aquaflow® (22.3% tau-fluvalinate). Both products killed > 90% of the nymphs within 14 d when applied as a 1% aqueous mixture for 60 s. Thus, Natur'l oil could be used instead of the pyrethroid as a dip to remove Madeira mealybugs from coleus cuttings.