• Introduction
• Evaluating the potential for natural recovery
  • Burn severity & plant survival
  • Noxious weed cover & survival
• Revegetating with competitive plants
  • When revegetation is necessary
  • Formulating a Seed Mix
  • Things to consider
• Establishing competitive plants
• Managing competitive plants
• Integrated Weed Management
• Preventing noxious weeds
• Eradicating small weed patches
• Managing large weed infestations
  • Mechanical control
  • Chemical control
    • Timing & placement
  • Cultural control
  • Biological control
• Monitoring & Evaluation
• Developing a burned-area IWM plan
• Summary
• Sources and Credits
• Additional Resources
• Interactive Exercises

Rangeland Weed Management - Managing large infestations through biological control

Biological Control

The noxious weeds of Montana (see Appendix A) are native to Eurasia. These plants arrived in North America without their coexisting natural enemies - diseases, parasites, predators, etc. In their native countries, natural enemies help keep the plant populations at stable densities. Upon these plants’ arrival in North America, the absence of natural enemies predisposed aggressive invasion and growth characteristics.

Biological control methods reunite a target weed with its host-specific natural enemies (see Table 3). Management by biological control has been effective on some large-scale weed infestations. However, biological control will not eliminate or prevent the spread of the target weed; it aims instead at reducing the density of the target weed to a stable, non-damaging level.

Insect biocontrols remove valuable fluids, defoliate, eat seeds, and bore into the roots, shoots and stems of target weeds. These feeding actions can greatly reduce the competitive abilities of the infestation by weakening and removing individual weeds within the infestation. At this stage in management, revegetation can be highly successful.

Biological control can be especially effective when integrated with other management techniques such as sheep-grazing, revegetation or herbicide treatments. If choosing integration with herbicides, separation between the insect biocontrol and the herbicide may need to be addressed to avoid damaging the biocontrol population. For instance, agents could be distributed in the middle of the infestation while treating the perimeter with herbicides.