Posted 28 January 2009. Crop Management.
Developing an Effective Weed Management Plan: the Importance of Mapping
Montana State University. extn.msu.montana.edu
Bozeman, Montana (January 26, 2009)--Efforts to control invasive plants are often described as a "war on weeds," and, by many estimates, the war is very hard to win. The intelligence gathered before any war is of vital importance to succeeding on the field of battle, and that is certainly the case in the war on weeds.
Conducting a weed inventory/survey is similar to gathering intelligence about the enemy, and should be designed to answer at least the following questions:
• What is the weed?
• Where is it located?
• How large is the infestation?
• Are there any desirable plants still growing with the weeds?
Although the most rewarding part of weed management may be killing them, collecting information about the weeds and their surroundings before applying control methods is worth the effort. Trying to manage weeds without such information may result in wasted time and money, or even failure. Information on presence, size and density of infestations is critical for planning control efforts. For example, low density, small infestations might be targeted for eradication through hand pulling, while high density, large infestations may require containment through herbicide applications. Mapping allows you to identify priority control areas and areas susceptible to future invasion. Mapping over successive years provides a means for measuring treatment success, and without it you may not know if you are making progress. Mapping is also a critical component of developing cooperation among land owners, defining each partner's responsibilities and obligations.
Understanding the differences between a weed inventory, weed survey and weed map can be helpful. A weed inventory is cataloguing the weeds in an entire management area, i.e. a census. A weed survey is a sample of a representative portion of the management area and would likely be conducted if it is not feasible to cover an entire management unit because of size and/or limited resources. Inventories and surveys are best used to demonstrate the weed distribution and provide a rough estimate of the total number of infested acres. Weed mapping is often used as a catch-all phrase for weed information gathering, recording and display techniques.
Monitoring is another term that often gets confused with inventory, survey and mapping. Monitoring is generally conducted at regular intervals at representative locations and can be designed to detect relatively small changes in weed numbers within an infestation. While inventories and surveys are typically a point-in-time record of weed infestations and levels, monitoring involves repeated measurements of individual weed patches or larger areas.
Information collected during monitoring may include density, height, biomass, canopy cover of weeds and may include photos taken from fixed points. These data can be compared from year to year and help to determine whether weed populations are increasing or management practices are being effective.
Weed mapping efforts should begin with setting goals and objectives.
Goals and objectives will guide the selection of the best field methods and help to ensure that the information collected is useful. Land use goals and realistic weed management objectives are critical to effective weed management. For example, your land use goal may be to maintain an adequate amount of forage for a specified number of cattle, and this may require reducing weeds to less than 10 percent canopy cover.
After establishing land use goals and realistic weed management objectives to meet those goals, you are ready to select a mapping method to help you meet your weed management objective. Including monitoring in your efforts will allow you to review the results of your management from time to time and help you to adapt your weed management plan as necessary to meet land use goals.
Another important initial decision to make is whether or not neighboring land managers will be involved. Often cooperative weed management areas are formed in which all participating members map their weeds using similar techniques. Information can be shared, and that can result in a more comprehensive control and prevention program that benefits an entire community or region.
To determine an appropriate mapping method, consider four basic inventory/survey categories: exploratory, reconnaissance, extensive and intensive.
Exploratory is the simplest category and is used when little or nothing is known about the location and types of weeds in a relatively large area. The purpose of an exploratory inventory/survey is to search as many acres as possible in the least amount of time, noting weed species presence, location and size of infestation.
Reconnaissance is used when abundance of common weeds is already known and maps indicating such basic information may already exist. The main purpose of reconnaissance is to find and record as many small patches of early-stage invaders as possible to allow for early detection and rapid response, and such efforts may be focused on areas most susceptible to new invasion (roads, trails, campgrounds, rivers, etc.).
Extensive inventory/survey should only be conducted after exploratory and/or reconnaissance work has been done, because it involves refining data to look for correlations between weeds and environmental factors.
Finally, an intensive inventory/survey obtains as much information as possible about weeds, other plant species, and environmental factors, and uses this information or a subsample of it as a baseline for monitoring.
When mapping weeds the following information should be collected for each infestation: weed species present, the size of the infestation, date, location description and the kind and preferably the amount of desired vegetation growing in association with the weeds. The size of the infestation is typically given in acres and may be divided into categories such as less than one acre, one to five acres, or greater than five acres. Finer categories would be desirable if recording change over time is a weed management objective. If possible, include the Universal Transverse Mercator or "UTM" coordinates, or latitude/longitude in the location description, which can be achieved by using a GPS unit to mark the infestation site.
Winter is a good time to plan for any weed mapping activities you may undertake come springtime. For more detailed information regarding weed mapping, refer to the Extension Bulletin "Inventory and Survey Methods for Nonindigenous Plant Species" (EB0171; $20), which is available from MSU Extension Publications (406) 994-3273, or MSU P. O. 172040, Bozeman, MT 59717. You also order the publication through your local Extension office.