SECTION A. INTRODUCTION Section contents Biological Control (Revised March 2021) . A-1 Using Pesticides Safely (Revised March 2020) . A-8 This handbook is designed as a quick and ready reference for weed Important Points to Remember control practices and herbicides used in various cropping systems or sites in Idaho, Oregon, and Washington. This handbook is not intended as a complete guide to weed con- trol or herbicide use. Authors have assembled the most reli- This handbook will be useful to Extension agents, company field able information available to them at the time of publication. representatives, commercial spray applicators and consultants, her- Due to constantly changing laws and regulations, authors can bicide dealers, teachers, and producers. assume no liability for the recommendations. Recommendations are based on research results from the Agricultural Any use of a pesticide contrary to instructions on the printed Experiment Stations and Extension Services of Oregon, Idaho, and label is illegal and is not recommended. Before using any Washington. A few suggestions are included from research conducted herbicide, read the label on the container. Before a herbicide in other states, and from U.S. Department of Agriculture research can be recommended for a specific use, it must be thoroughly centers. In all cases, authors make every effort to list only registered her- tested. The recommendation on the manufacturer’s label, bicides, and to ensure that the information conforms to product labels when followed, can prevent many problems arising from the and company recommendations. improper use of a chemical. Revision and Availability This handbook is updated annually. Trade-name products and services are mentioned as illustra- Individual sections are revised once each year; revision dates are tions only. This does not mean that the participating Exten- listed at the start of each section. Most sections are also available as sion Services endorse these products and services or that they PDF documents on the weed handbook website: intend to discriminate against products and services not men- http://pnwhandbooks.org/weed tioned. Commonly recognized trade names (brand names) Some sections may include additional online content, such as photos of some commercial pesticides are used in this handbook to and links to related websites, publications, and other resources. help identify the common name used by the Weed Science Society of America (WSSA), not as recommendations for that Please send comments or suggestions to handbook editor particular product. Ed Peachey ([email protected]). Biological Control Jennifer E . Andreas, Joseph Milan, Carol Randall, and Joel Price Revised March 2021 Classical biological weed control involves the introduction and in controlling Mediterranean sage, St. Johnswort (Klamath weed), management of selected host-specific natural enemies to reduce tansy ragwort, Dalmatian and yellow toadflax, purple loosestrife, and suppress problematic non-native weeds. The majority of the diffuse knapweed, and leafy spurge. Pacific Northwest’s weeds are exotic, originating from other con- Biocontrol is a slow process, and its efficacy is highly variable. Since tinents. These newly introduced plants, freed from the natural it can take several years for biological control agent (BCA) popula- enemies found in their native range, gain a competitive advantage tions to build to levels capable of weed suppression, many BCAs over native plants which allows the introduced plants to become have not been present or studied long enough in the Pacific North- weedy. Once weed populations become well distributed, herbicides, west to determine their ability to control their host weed. Only after cultural, and mechanical methods of weed control are not always monitoring target weed and BCA populations over time will the economical or physically able to meet weed management objec- impact of newly introduced BCAs become evident. tives. Classical weed biological control (biocontrol) is a weed man- agement tool that is inexpensive, self-sustaining, and host-specific BCAs impact their target weeds directly and indirectly. They directly and may help reduce the negative impact of weeds, particularly impact weeds by destroying plant tissues and interfering with plant where other control methods are not feasible. functions. BCAs cause indirect impact by increasing stress on the weed, which may reduce its ability to compete with desirable plants. Biocontrol differs from other weed control methods because it does not result in immediate weed population reductions. Successful Biocontrol can be integrated with other management practices to biological control reduces the competitive ability of target weeds, reduce target weed populations. For example, once weeds are weak- allowing other plants to successfully compete with and suppress ened by BCAs, competitive plantings can reduce the availability of target weed populations through time. Unlike other weed control light, water, and nutrients to already stressed weed populations. In options, biocontrol rarely causes substantial weed population re- addition, satellite weed populations can be controlled by herbicides ductions in the initial year of release; however, successful biocontrol or physical means to reduce weed spread while BCAs attack the can result in significant, sustained weed reductions over a period primary infestation. of years. In the Pacific Northwest, biocontrol has been successful PNW Weed Management Handbook A1 Similar to other weed control methods, biocontrol is not a silver management methods. Interdisciplinary vegetation management bullet; it will not eradicate all of the target weed since a BCA’s sur- teams are working strategically to find the best single or combina- vival depends on the presence of its host plant. Therefore, when tion of weed control tools to minimize adverse environmental and using BCAs, expect weed populations to persist, but at much lower socioeconomic impacts. levels. After target weed populations decrease, populations of BCAs If you are considering importing BCAs from another state, be aware will decrease correspondingly. This is a natural cycle. A resurgence that federal interstate transport permits may be required. For more of weed populations may occur due to seed reserves in the soil, host information, contact your nearest USDA APHIS PPQ office, or visit weed plants missed by the BCA, and lagging populations of BCAs. https://www.aphis.usda.gov/aphis/ourfocus/planthealth/import-in- In areas where the BCAs do not provide sufficient control, other formation/permits/regulated-organism-and-soil-permits/biological- weed control methods may need to be integrated to achieve desired control-organism-permits or your state weed biocontrol specialist. results, or a search for additional BCAs may be pursued. Permits for approved BCAs are free but take time to review and issue The BCAs released in the Pacific Northwest have been tested to so it is best to apply well before your anticipated ship date. ensure they are host-specific (i.e., they will only feed on the host Anyone who implements classical biological weed control is en- weed species). Host-specificity testing is an expensive and time- couraged to follow the International Code of Best Practices for Clas- consuming task that must be done before a BCA is allowed to be sical Biological Control of Weeds, adopted by the delegates at the introduced into the United States. Some candidate BCAs, which 1999 International Symposium on Biological Control of Weeds. The could be effective in reducing target weed populations, may not twelve codes for safe and effective biocontrol practices can be found be approved for introduction because they are not host-specific at http://www.invasives.wsu.edu/Code.htm. Briefly, the key guide- enough. A candidate BCA that is not sufficiently host-specific will lines for biocontrol implementation includes: be rejected for release in the United States to ensure that the BCA, in the absence of its host weed, will not move to crops, native flora, • Releasing only safe and approved BCAs. or endangered plant species. • Using the most effective BCAs. Biocontrol of certain weeds may not work in your area, even if it • Documenting releases. State agencies can provide release does elsewhere. BCAs require specific conditions to survive and forms and appreciate receiving release information for their thrive. Climate variations (e.g. cold winters), plant biotype differ- records. ences, and nearby insecticidal treatments (e.g. mosquito abate- ment or agricultural pest insect control) may account for some • Releasing only the intended target BCA by thoroughly remov- past biocontrol failures. To maximize success, trained personnel ing all other insects and plants from collecting material. should supervise and monitor biocontrol efforts. To monitor BCAs, • Stopping releases of ineffective BCA, or when control is the Standardized Impact Monitoring Protocol (SIMP) is recom- achieved. mended. More information on SIMP can be found by accessing the • Monitoring for impacts on the host weed, non-target species, ISDA/BLM biocontrol website (http://invasivespecies.idaho.gov/ and the environment. bio-control-monitoring). Once release sites for BCAs have been selected, protecting those areas from disturbance so BCAs can get established is essential. As highlighted in the code of best practices, do not use non-APHIS Initial BCA releases often consist of a small number of individual approved natural