Testing the efficacy of specialist herbivores to control Lepidium draba in combination with different management practices

摘要

Lepidium draba L. [=Cardaria draba (L.) Desv.; Brassicaceae] is a perennial mustard, indigenous to Eurasia. In the 18th century, L. draba was introduced into North America, where it is now listed as noxious in 16 states and three Canadian provinces. In 2001, a biological control program was initiated investigating the possibilities for biological control of L. draba in North America. To determine whether specialist herbivores are actually limiting population growth of L. draba in its area of origin and how their effect might interact with soil nutrients and management regimes, we established manipulative field experiments in Spring 2006 in eastern Romania, where five of the currently studied biological control agents are present. Plots (3 x 3 m) were established in already existing L. draba stands, and four treatments applied in a split-plot design: (1) grazing (yes, no); (2) cultivation (none, shallow, shallow + sowing of grasses/legume mix; (3) pesticide application to exclude herbivores and/or augmentation of specialists (yes, no) and (4) carbon addition in the form of sawdust to reduce plant available soil nitrogen (yes, no). First results indicate that cultivation and cultivation + sowing reduced the number of L. draba plants, however only atthe beginning of the field season. As expected, neither pesticide nor sawdust applications had an effect on plant numbers or plant vigor in the first year; they will probably need more time to become apparent. We expect that grazing treatments, which will start in May 2007, will probably have the largest effect on L. draba vigor and densities. Final results should allow us to develop recommendations for an integrated management strategy for L. draba.