Glyphosate-resistant hairy fleabane documented in the Central Valley

Hanson, B; Hembree, K; Shrestha, A

Glyphosate-resistant hairy fleabane documented in the Central Valley

Authors

Bradley D. Hanson
Kurt J. Hembree
Anil Shrestha

Authors Affiliations

B.D. Hanson is Research Agronomist, U.S. Department of Agriculture/Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, Parlier; K.J. Hembree is Farm Advisor, UC Cooperative Extension, Fresno County; A. Shrestha is Integrated Pest Management Weed Ecologist, UC Statewide IPM Program, UC Kearney Agricultural Center, Parlier.

Publication Information

Hilgardia 62(3):116-119. DOI:10.3733/ca.v062n03p116. June 2008.

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Abstract

In recent years, growers and pest consultants have reported poor control of the weed hairy fleabane in some areas of the Central Valley. Hairy fleabane seeds were collected from Esparto, Fresno and Reedley, Calif., and greenhouse-grown seedlings were treated at several different glyphosate rates and compared with an untreated control. None of the Esparto or Fresno plants survived glyphosate rates greater than 0.78 pounds acid equivalent per acre (lb ae/ac), while some of the plants from Reedley survived even the highest rate of glyphosate tested (12.4 lb ae/ac). The dose required to reduce plant dry weights by 50% (GR₅₀) of the Esparto plants ranged from 0.28 to 0.30 lb ae/ac, whereas the GR₅₀ of the Fresno and Reedley plants ranged from 0.26 to 0.61 and 0.92 to 2.88 lb ae/ac, respectively. This study showed that the hairy fleabane plants from Reedley were much more tolerant of glyphosate than either of the other two biotypes and, based on the GR₅₀, the level of resistance ranged from 3-to 10-fold greater.

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