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1 June 2005 Limonene, a Citrus Extract, for Control of Mealybugs and Scale Insects
Robert G. Hollingsworth
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In a series of bioassays with mealybugs, aqueous solutions of 1% limonene were tested that used from 0.50 to 1.50% all purpose spray adjuvant (APSA)-80 as an emulsifier/surfactant. The two ingredients were added to water or to 0.1% Silwet L-77, an agricultural surfactant. Using 1% limonene, 0.75% APSA-80 and 0.1% Silwet L-77, a semitransparent mixture (primarily a microemulsion) was obtained that was safe for most plants and provided good control of mealybugs when sprayed or used in 1-min dips. Used at half strength, this mixture controlled ≥99% of whiteflies, whereas the full-strength mixture controlled from 69 to 100% of mealybugs and scales, including ≥93% control of root mealybugs. In side-by-side greenhouse tests, this mixture was superior to a 2% solution of insecticidal soap or a 2% solution of horticultural spray oil. Mortality of green scales on potted gardenia plants averaged 95, 89, and 88% on plants sprayed with limonene, insecticidal soap, or horticultural oil, respectively. In a related test, these same sprays killed 44.1, 22.7, or 12.5% of third and fourth instar clustering mealybugs, respectively. Limonene has promise as a safe, natural pesticide for insect pests on tolerant plants. Although 1% limonene solutions damaged certain species of ferns, gingers and delicate flowers, they caused no damage to ornamentals with thick, waxy leaves, such as palms, cycads, and orchids.

Robert G. Hollingsworth "Limonene, a Citrus Extract, for Control of Mealybugs and Scale Insects," Journal of Economic Entomology 98(3), 772-779, (1 June 2005).
Received: 1 October 2004; Accepted: 1 February 2005; Published: 1 June 2005

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