5. Perennial pepperweed, Lepidium latifolium In cooperation with H. Hinz and E. Gerber, CABI, Delemont, Switzerland; R. Hayat and L. Gultekin, Ataturk Univ. of Erzurum, Turkey; R. Ghorbani and A. Ghorbanali, Ferdowsi Univ., Mashhad, Iran; and Livy Williams, USDA ARS, Reno, NV, USA. Lepidium latifolium is a herbaceous, semi-woody perennial that typically reaches 0.5–1.5 m in height and reproduces vegetatively and by seed. Plants regrow early each year from a dense network of creeping, horizontal roots, flower in June/July, and set seeds in July/August. It is a prolific seed producer, capable of producing more than six billion seeds per acre of infestation. This weed is native to central Asia and is believed to have been introduced into the United States through California around 1900 as a contaminant of sugar beet seeds. Now, it is widely distributed in western United States, costal New England, Mexico and Canada. Perennial pepperweed is often associated with mesic habitats, such as river banks, drainage ditches, and subirrigated pastures and hay meadows. However, it can invade a wide range of habitats including pastures, open fields, roadsides and residential areas. It is highly competitive and invasions result in dense monocultures and subsequent loss of biodiversity through the exclusion of native vegetation. In agricultural settings, the species competes with crop plants and reduces agricultural yields. In rangelands it decreases the quality of hay and reduces livestock-carrying capacity. In addition, it produces secondary plant compounds that are reported to be toxic to livestock. This weed is difficult to control because of its large, stout root system. Mechanical or cultural control techniques usually provide no permanent reduction of populations. In 2006 CABI E-CH and BBCA decided to share resources and collaborate closely in their effort developing biological control for Lepidium latifolium. Since then, field surveys have been conducted in cooperation and some of the results of both research teams are presented in the following paragraphs.
5.1. Summary of 2007 activities Field surveys in part of the likely area of origin of perennial pepperweed were continued in 2007. Six field trips were conducted, two to central and north-eastern Turkey and one each to southern Russia, western China, southern Ukraine and Iran. The field trips to Turkey, Russia and China focused on collecting potential biological control agents already prioritized in 2006, while surveys in the other countries aimed to find new potential agents. As in 2006, surveys in Turkey were conducted in cooperation with Prof. Rüstem Hayat and Dr Levent Gültekin (both Atatürk University, Erzurum). Special emphasis was given in 2007 to studying the biology of Melanobaris sp. n. pr. semistriata in the field and to collecting adults of this root-mining weevil to conduct host-specificity tests in quarantine at CABI Europe – Switzerland (CABI E-CH). Further, the field
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