pyrethrum

noun

py·re·thrum | \ pī-ˈrē-thrəm

Definition of pyrethrum

1 : any of several chrysanthemums with finely divided often aromatic leaves including ornamentals as well as important sources of insecticides

2 : an insecticide made from the dried heads of any of several Old World chrysanthemums (especially Chrysanthemum cinerariaefolium)

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Some gardeners mention pyrethrum as an option for the nymphs, but for the adults, malathion and Sevin are the effective options. — Calvin Finch, ExpressNews.com, "How to stop the bugs eating your tomatoes, peaches," 21 June 2019 Nymphs can be controlled with insecticidal soap, pyrethrum, rotenone or neem. — Ellen Nibali, baltimoresun.com, "Garden Q&A: Black-eyed Susans with fungal leaf spot disease," 11 July 2017

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'pyrethrum.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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3 Jul 2019

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The first known use of pyrethrum was circa 1543

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pyrethrum

noun

py·re·thrum | \ pī-ˈrē-thrəm

, -ˈreth-rəm

Medical Definition of pyrethrum

1 : any of several chrysanthemums with finely divided often aromatic leaves including ornamentals as well as important sources of insecticides

2 : an insecticide consisting of or derived from the dried heads of any of several Old World chrysanthemums (genus Chrysanthemum of the family Compositae)