Submitted to: Washington State Hay Growers Annual Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: January 4, 2010
Publication Date: January 13, 2010
Citation: Boydston, R.A. 2010. Managing puncturevine in alfalfa hay and along field edges. Washington State Hay Growers Association 2010 Conference. Jan. 13-14, Kennewick, WA, pp.45-47. Technical Abstract: Puncturevine (Tribulus terrestris) is a nuisance and difficult to control weed in alfalfa hay field edges and borders. Puncturevine contaminated hay can contain high levels of nitrates and burs can injure mouths of livestock, lowering the value and quality of the hay. Puncturevine is a summer annual weed with spiny fruits that split into five segments, each containing one to four seeds. The seed nearest the pointed end of the bur is the largest and usually germinates first following an after-ripening period of six months. In alfalfa, preemergence applied flumioxazin and norflurazon control early season puncturevine germination. Imazamox, 2,4-DB, and bromoxynil applied postemergence can control puncturevine seedlings less than 4 cm tall. Once burs with viable seed are produced on plants, many growers remove the entire plants and dispose them to prevent attached burs from adding to the soil seed bank. The spiny fruits (burs) mature at different times on the plant and some burs may fail to produce viable seed if the plant is killed by hoeing or if sprayed with an effective herbicide. The viability and germination of puncturevine seed from burs of various maturity harvested from plants that were treated with of 2, 4-D, glyphosate, and imazethapyr were determined. Applications of 2,4-D greatly reduced puncturevine seed viability and germination by 50% or more from burs that were on the plants at the time of herbicide application compared to glyphosate and imazethapyr, which had little effect. Radicals emerging from 2,4-D treated burs were swollen and failed to elongate. No seedlings emerged from burs planted in soil that were derived from 2,4-D treated plants. Spraying puncturevine plants in field borders with 2,4-D once burs have formed on plants could greatly reduce puncturevine emergence in subsequent years and allow for grass cover to establish, further reducing puncturevine’s ability to establish.