Yellow Starthistle Information

 Mech control
   -hand
   -tillage
   -mowing

 Cultural control
   -grazing
   -burning
   -re-vegetation

 Biocontrol
   -insects
   -biocontrol table
   -plant pathogens

 Chem control
  - risks
    --spray
    --water
    --toxicology
    --herbicide resist
    --effects
   -herbicides
    --preemergence
    --postemergence
    --late season
    --pre- & post-
    --imazapic
    --clopyralid
    --picloram

 Integrated app

 Summary

Management

Integrated approaches

Most often a single method is not effective in the sustainable control of a range weed. A successful long-term management program should be designed to include combinations of mechanical, cultural, biological, and chemical control techniques. There are many possible combinations that can achieve the desired objectives, but these choices will have to be tailored to the site, economics, and management goals. Sometime the control techniques must be in a particular sequence to be successful. For example, in a re-vegetation effort along a yellow starthistle infested canal and roadside the first step was to intensively manage starthistle (Brown et al. 1993, Thomsen et al. 1994). The second step was to reseed with deep-rooted native perennial grasses. In the final stage, native broadleaf forbs such as California poppy and lupines were seeded into the system.

In another study, a long-term integrated approach for yellow starthistle control using combinations of grazing, mowing, and clover plantings (Thomsen et al. 1996a, 1997). For example, seeding with subterranean clover, grazing three times, and mowing once at the early flowering stage resulted in 93% reduction in yellow starthistle seed production and a dramatic increase in standing dry matter (Thomsen et al. 1996a). In another experiment, two timely repeated mowings combined with a subterranean clover planting gave nearly complete control of yellow starthistle (Thomsen et al. 1997).

In Australia, the technique of applying sub-lethal applications of 2,4-D amine in combination with heavy stocking rates of grazing sheep has been a long accepted integrated approach for control of thistles (Dellow 1996).

Using another integrated approach, Pitcairn et al. (1999a, 2000a) hypothesize that combining clopyralid applications with insect biocontrol agents might provide for more effective long-term control of yellow starthistle. Clopyralid applications would reduce plant density and the seed bank. The attack of biocontrol insects on escaped plants in subsequent years should slow the rate of re-infestation by impacting the few seedheads available. Results thus far indicate that the combination of biocontrol agents suppressed seed production by 76% in 1997, and 43% in both 1998 and 1999 (Pitcairn and DiTomaso 2000). In addition, the reduction in starthistle resulting from the herbicide treatment did not affect the ability of the insects to attack the seedheads of escaped plants. It is hoped that seed destruction by the established biological control agents can retard resurgence to 4-6 years and thereby reduce the need for continuous herbicide treatments. This would lower the economic costs required for effective long-term management of yellow starthistle.

A number of other studies are underway to assess various combinations of techniques for starthistle control. UC researchers are investigating the effectiveness of integrating summer prescribed burning and clopyralid treatment. The objective is to determine which sequence is likely to have the greatest benefit for rangeland health, as indicated by plant species diversity and by forage quality and quantity.

In a multi-agency large-scale study at Fort Hunter Liggett in southern Monterey County, researchers are testing integrated approaches combining spring and summer herbicide applications, prescribed burning, and biological control agents. Five-year management plans have been developed for open grasslands 1) used primarily for military training, 2) surrounded by valley and blue oaks, and 3) with rare plants or species of concern. The goal of each of these management plans is to control yellow starthistle, enhance the integrity and utility of the ecosystem, and prevent re-invasion.

As previously described, re-vegetation projects for yellow starthistle control nearly always rely on integrated strategies. In most cases, it is difficult to establish desired plants without the management of competing vegetation, including starthistle and annual grasses. The goal of these re-vegetation projects is to develop sustainable high quality range conditions and improved wildlife habitat capable of providing long-term starthistle control without the need for continued herbicide treatments or other expensive management tools.

In a project on severely degraded rangeland in northern California, an integrated combination of clopyralid treatment and pubescent wheatgrass seeding (see re-vegetation section) was shown to be very effective in suppressing yellow starthistle seed production and providing a better long-term solution than applying clopyralid alone (Enloe et al. 1999a, 1999b). This strategy is also compatible with the survival of yellow starthistle biocontrol agents. With the integration of these insects, it is possible that starthistle seed production will be reduced, further slowing the re-infestation rate.

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