Biology and Biological Control of Knapweed

Wilson, L. M. and C. B. Randall. 2003. Biology and Biological Control of Knapweed. USDA-Forest Service FHTET-2001-07. 2nd Edition.

Chapter 3: Elements of a Knapweed Biological Control Program

This chapter discusses the elements necessary to successfully operate a knapweed biological control program. Biological control programs require years of continuous observations and a commitment to specific steps or processes.

A systematic process to establish a knapweed biological control program consists of the following elements:

1. Selecting and preparing study sites
2. Collecting biocontrol agents
3. Transporting biocontrol agents
4. Releasing biocontrol agents
5. Monitoring
   1. Biocontrol agents
   2. Vegetation (quantitative and qualitative)
   3. Establishing photo points

Methods for carrying out each of these processes are discussed in separate sections in this chapter. (For solutions to common problems encountered when establishing a biocontrol program, see Appendix A.)

1. Selecting and Preparing Release Sites

Biocontrol sites are characterized in three ways: 1) study, 2) nursery, and 3) field release site.

Study site. A study site is a release site where the damage and impact is evaluated. Study sites can be used as demonstration areas for educational and training purposes, and can be monitored intensively to determine the effects of bioagents on knapweed over time. However, demonstration and monitoring activities at the study site should be planned carefully because frequent site visits can damage the site through disturbance and trampling of vegetation.

Nursery site. A nursery site, or field insectary, is used to grow large quantities of surplus bioagents for redistribution to other knapweed infested areas where bioagents have not been previously released or are of low density. Nursery sites should be left undisturbed for 3 to 5 years to allow the bioagent populations to increase. Careful monitoring will determine when the bioagent population is large enough to enable collection for redistribution. It is essential that nursery sites receive minimal disturbance.

Field Release. A field release site is simply an open site for general control purposes. Monitoring or redistribution efforts are not planned for these sites.

Pesticides. Select sites which are pesticide-free (no herbicides and insecticides have been or will be applied to the area).

Landowner consent. The landowner/manager must be willing to have the release site available for visitations and monitoring over several to many years. Consent is particularly important when planning a study or nursery site. When getting permission to use a site, be sure to secure the following:

1. Written permission from the landowner or land manager allowing use of the area as a release site.
2. Written agreement by the landowner allowing access to the site for monitoring and collection for a period of at least six years (three years for establishment and buildup and at least three years for collections).
3. Permission to put a permanent location marker at the site.

Preparing the Site

Preparing the release site involves the following activities:

• Determine the need. Look for presence of bioagents before the release is made. Some knapweed bioagents are so common and widespread that it is no longer necessary to redistribute them; for example, it is likely that the two Urophora flies (U. affinis and U. quadrifasciata) are already present. If so, it will not be necessary to release these flies at this site.
• Establish a permanent location marker. After selecting a site, choose a dense, uniform patch of knapweed in which to place a marker. Use white wood or metal stakes to mark the exact location of the release site. Stakes must be tall (4 feet [1.2 m]) and highly visible so they can be found easily on future visits.
• Set up a photo point. A photo point is used to photographically record changes in knapweed infestation (decline or increase) over time following release of bioagents at a site. Use a permanent feature in the background as a reference point.
• Draw a map. A map and written directions to the study site are essential for other people to locate the site. Note permanent roads, creeks, rivers, mile markers, etc. Include a legal description or latitude and longitude global positioning system (GPS) coordinates so that the site can be easily re-located.
• Monitor baseline vegetation. In study sites where vegetation will be monitored, baseline data are used for comparing knapweed infestation measurements before and after releasing bioagents in the area. It is always useful to collect baseline vegetation data even at nursery or field release sites.

2. Collecting Biocontrol Agents

Planning and timing of collection is critical. The type of bioagent and the knapweed species will dictate the best time in the season to collect. Ensure that all necessary collection supplies are on hand. Also, accurate identification the bioagents is essential.

Whether collecting larvae or adults, follow these general guidelines.

General Collection Guidelines

Quantity. The minimum needed to optimize establishment is 200 bioagents per site, but more is better.

Containers. Use "breathable" containers at all times. Breathable containers allow air flow to the insects and will not form condensation. One of the best containers to use is a pint-sized, nonwaxed ice cream carton. These are sturdy and breathable. Paper bags can work as temporary containers if care is taken to keep the bag from getting wet or squashed. Do not use plastic bags as containers because they are airtight and will not release moisture. Put a small wad of paper toweling in the container to absorb moisture and to give the insects a crawling surface.

DO NOT USE PLASTIC BAGS AS CONTAINERS

Cooling. Keep bioagents shaded and cool at all times while collecting, sorting, counting and transporting. Bring a cooler with pre-frozen blue ice packs to the field. Secure an ice pack to the interior side of the cooler so that it does not roll around and crush the bioagents (see Fig. 52).

Sorting. Sorting is done after collecting to separate the insects from other organisms and debris, such as weed seeds, collected along with the insects. Empty the contents of the sweep net onto a tray and aspirate or hand-pick the insects out of the debris. For fast moving insects, keep them in the net and grip the top of the net at the rim. Slowly loosen your grip to open the top of the net and collect the insects as they attempt to escape (insects will always move toward the light). If the collected material is first chilled, the insects (especially beetles) move slower and are easier to collect.

Care. Exercise care in handling bioagents. Difficulties that may be encountered when collecting bioagents are identified in Tables 9 and 10 (see also Appendix A).

KEEP INSECTS COOL AND SHADED WHILE COLLECTING
SORTING, COUNTING OR TRANSPORTING THEM

Table 9.  Level of difficulty in collecting knapweed seedhead feeders.

¹Level of difficulty: • (easiest) to ••••• (most difficult)

Table 10.  Level of difficulty in collecting knapweed root borers.

¹Level of difficulty: • (easiest) to ••••• (most difficult)

Planning and Timing

Planning and timing of bioagent collection is critical. It involves knowing where, when, how, and what to collect.

Where to collect

Collect from nursery sites or open field sites that have an abundance of insects. You may wish to consult with your county extension educator, university or state entomologist, or county weed superintendent for an appropriate site.

When to collect

Determine the collection and release date(s) using the recommended timetables for knapweed seedhead feeders and root borers (Tables 11 and 12) as guidelines.

• Due to varying emergence time for individual insects, adult weevils can be seen at other than the optimal emergence periods given in Tables 11 and 12. However, for the greatest success in collecting adult bioagents, collect them during the peak emergence period.

• When sweeping for insects, the best time to collect is during the heat of the day (between 1 and 6 p.m.) because bioagents are more active at that time. Exceptions are Sphenoptera adults, which are nocturnal; the best time to collect them is early on warm evenings.

• Wait for a good day. Do not collect in the rain. Flying insects will not be around during a rain; crawling beetles will hide in protected niches and become more difficult to find. Excess moisture problems also occur easily when both the collected bioagents and collection containers get very wet.

How to collect

Choose a collection method to use for the desired life stage (larvae or adults) of the insects (see Tables 11 and 12). The best collection method is the one that 1) produces the greatest number of insects in the least amount of time and effort, 2) produces insects in the best condition, and 3) requires the least handling and sorting (clean collection). The six typical collection methods are as follows: sweep net, aspirator, handpicking, tapping (stick and bucket), black light, and seedhead collecting.

• Sweep net. A sweep net is made of cotton or muslin on a hoop, 10 to 15 inches in diameter, attached to a handle 3 feet (0.9 m) long (Fig. 47). As its name implies, it is used to "sweep" insects off the knapweeds. The sweep net method is recommended for collecting adult beetles. It is relatively easy and efficient. It is best to alternate between sweeping insects off the knapweed and aspirating them out of the net. Sweep no more than 25 times before aspirating (Fig. 48). This reduces the potential harm that could result from knocking the bioagents around with debris or other insects inside the net (Tables 11 and 12). Flies are very delicate, thus collecting them with sweep nets can be harmful or fatal. For this reason, sweep-netting is not recommended for collecting flies. Sweep-netting delicate moths can also be harmful. When collecting adult moths, gently sweep the top half of the plants 7 to 10 times and immediately remove the moths from the net.

  

  Figure 47. Sweep net

  

  Figure 48. Sweeping for insects

• Aspirator. Use an aspirator (Fig. 49) to suck the insects from the knapweed or the sweep net. It is sanitary (no unwanted or unknown material is inadvertently collected and assures the identity and quantity of the agent being released). Aspirating can be done in the field or indoors. When aspirating indoors, cool the insects to make them inactive and easier to aspirate. Seal and label the carton with the species, number of bioagents, collection site and date. Do not use mouth aspirators for collecting adult moths because the scales from moth wings can break off during collection and get inhaled (by the collector).

  A vacuum aspirator is another device for collecting insects, especially adult moths. It is faster and more sanitary than a mouth aspirator. However, vacuums are cumbersome and not as easy to transport and use as a sweep net and mouth aspirator.

  

  Figure 49. Aspirators for collecting biocontrol agents. - Manual

  

  Figure 49. Aspirators for collecting biocontrol agents. - Hand held vacuum, gasoline or battery powered.

• Hand-picking. Simply pick the insects from the knapweed by hand (with the aid of a pair of forceps, if desired). Hand-picking works best for stationary or slow-moving insects like the weevils Bangasternus fausti and Cyphocleonus achates. Larinus beetles can be hand-picked from plants on windy days as they cling tightly to the plants and resist the sweep net.

• Tapping. If a sweep net is not available, tapping is the easiest collection method to use for collecting weevils. Using a stick (a badminton racquet works well), gently tap the knapweed stems into a bucket to remove the weevils. Separate the weevils further from unwanted debris and other plant materials, then place them in a breathable container. Use a funnel to aid in trapping the weevils into the bucket. To make a funnel, cut a plastic soda pop bottle in half, invert the small neck into the bottom and tape the two pieces together. Do not use funnels of this type for flies or moths.

• Black light method. Black ultraviolet (UV) lights attract moths at night. This method is used to monitor the nocturnal Agapeta zoegana. To use, suspend the black light from a post or set it up on top of a vehicle. Put a white sheet beneath the lights and on the ground to collect the moths that land on the sheet. Either hand-pick or use a vacuum aspirator to collect the moths and place them in a container.

What to collect

Biocontrol agents are collected as larvae, pupae and adults (see Tables 11 and 12 for the appropriate life stage in which to collect bioagents).

Collecting adults

Of the three types of knapweed insects (flies, moths and beetles), the beetles are best collected as adults. Fly and moth adults are more delicate than beetles and can be easily harmed or killed during collection. The ideal weather for collecting insects is a sunny, warm day with a slight breeze. It is best to collect bioagents when they are mating to collect both males and females and to ensure that eggs will be laid at the new site. If the insects are not mating and a collection is made too early or too late, the collection may be mostly one sex and the new population may not establish at the release site.

Collecting larvae

Rearing flies indoors

Collect several hundred dry seedheads from last year’s plants and put them in labeled paper bags. Once indoors, adults will likely emerge in a few weeks, so time the collection of heads carefully. You do not want adults to emerge too early and be out of synchrony with the knapweed plants, so collect heads a few weeks before flies would normally emerge outdoors. Empty infested seedheads from bag into a clear, breathable container such as a covered terrarium or in a rearing cage (Fig. 51). Leave the heads at room temperature. In 2-3 weeks, adult flies or moth will begin to emerge from the seedheads. Collect the adults that emerge, package and release them at the new site, or ship them to a cooperator.

Table 11.  Recommended timetable for collecting knapweed seedhead feeders for redistribution.

Table 12.  Recommended timetable for collecting knapweed root borers for redistribution.

3. Handling Biocontrol Agents

How the bioagents are handled after collection and transported to the release site can affect whether the bioagents will survive and multiply at the new site.

This section contains guidelines for transporting and shipping the bioagents.

Transporting the Bioagents

How the bioagents are handled and transported can greatly impact whether they become established. It is best to redistribute the bioagents immediately after they are collected to prevent injury to the specimens, within 24 hours if possible.

• For immediate redistribution. Store the insects in a breathable container with fresh knapweed foliage, crumpled tissue paper or paper towel.

• For later redistribution. Store the insects in a refrigerator. Bioagents can last up to three days in a refrigerator; however, only one day of refrigerated storage is recommended. For storage longer than one day, follow the guidelines for keeping bioagents alive during transportation, shipping or storage.

• Seal and label the container. Seal with tape and label the container with the name of the bioagent, the quantity collected, and collection date. Tape a blue ice pack to the bottom of the cooler to avoid physical damage. Put a barrier (e.g., newspaper) between the ice pack and the biogents to protect the bioagents from excess moisture or cold.

DO NOT ALLOW CONTAINERS TO TOUCH THE BLUE ICE PACK

Supplies Needed

• Breathable container
• Masking tape
• Paper towel or styrofoam (for transporting)
• Cooler
• Blue ice pack
• Cardboard box (for shipping)

Shipping the Bioagents

To ship bioagents over a long distance, plan the route and timing of shipments to prevent undue delays and stress on the bioagents. Ship the agents by overnight courier and advise your cooperator as to when they are being shipped, when they can expect to receive them, and to release the insects immediately. Try to collect on Sunday or Monday and ship Tuesday so shipments can be received before the weekend. Avoid shipping late in the week, and be aware of holidays, etc, that can delay shipping. Overall, observe the following guidelines:

• Know the regulations. Observe appropriate rules, restrictions and regulations pertaining to shipping bioagents to a cooperator or moving bioagents out of the county or state. For the current regulations, contact your local weed district, cooperative extension agent, the state Department of Agriculture, or the USDA Animal and Plant Health Inspection Service (APHIS).

• Prepare the bioagents. Sort the bioagents from all other unwanted material to avoid contamination at the receiving site. Put bioagents in shipping containers with enough space to allow the insects to move about within the container. Do the following:

  • Provide the insects with a crawling surface by lining the container with crumpled tissue paper or paper towel.
  • Do not put food or water in the container.
  • Tape lids on the containers and make sure the biogents do not get caught on the sticky part of the tape.
  • Pack the shipping container with care. Tape the blue ice packs to the inner side of the chest and pack with a layer of paper to absorb condensation (Fig. 52). Keep the bioagents cool until they are shipped.

Figure 52. Styrofoam-lined shipping box containing blue ice pack and biocontrol agent cartons

Summary: Care of the Bioagents

• Provide the bioagents with a crawling surface such as crumpled paper towel or tissue.

• Avoid physical damage to the bioagent by taping down potentially harmful objects, such as blue ice packs.

• Ensure that predators (i.e. spiders) are not trapped with the bioagent in the container by sorting bioagents before packaging them.

• Provide container with adequate ventilation. If necessary, punch holes in the lid with a pin.

• Do not expose bioagents to heat above 80º F (26ºC). Keep shipping containers in a cooler out of direct sunlight.

• If release or shipping is not immediate, store the bioagents in refrigerators no colder than 40º to 50º F (4ºC) for a no longer than 2 days or keep them in an ice chest until the bioagents are ready to be shipped or transported. Longer storage decreases the bioagents’ chance for survival at the new site.

Common Mistakes

• Excess heat. Do not expose bioagents to direct sunlight
• Excess moisture. Remove spilled or excess water in the container
• Lack of air. Provide adequate ventilation; use only breathable containers.

4. Releasing Biocontrol Agents

Timing of the bioagent release will determine whether the bioagents will survive and flourish at the new site. Follow these steps for releasing bioagents:

1. Place the permanent location marker. Release the insects at the location marker. This location will be later used to monitor activities.

2. Make the release. Consult Table 13 to determine the appropriate method to use for releasing each insect.

3. Take pictures. Take a series of photographs to record the release. A photo point will record the change in the site over time.

4. Collect baseline vegetation data. Choose a monitoring method listed in Tables 14 and 15. Establish baseline data at the time of the release. Use the same monitoring method every year.

5. Fill out and submit a release form. Complete the Biological Control Agent Release Form (see Appendix B). Submit the form to your county extension educator, university or state department of agriculture. Keep a copy for your records.

Table 13.  Appropriate release method for each bioagent.

Table 14.  Recommended timetable for monitoring knapweed seedhead feeders.

Table 15.  Recommended timetable for monitoring knapweed root borers.

• Direct placement of fly-infested heads. The easiest method for releasing flies and the seedhead moth is to place bouquets of infested plants at the new site. Collect last year’s plants in late winter, tie them into bouquets, take them to the new site and secure the bouquets to fence post or stake. Adults will emerge later in the spring as usual and colonize the new site. Retain 50 heads from the bouquet, put them in a labeled paper bag or dry container and allow the insects to emerge indoors, so that you know for sure which species you released at the new site. You can also estimate the number released based on how many adults emerge from the 50 heads.

• Open-field release. When releasing adult weevils, moths or flies, place the bioagents on the ground within a 3 foot radius of the permanent location marker under knapweed plants where they can continue to mate and disperse on their own.

• Caged release. An alternative to open-field release is to put the insects in a release cage or tent (Fig. 54). The bottomless tent, placed over a patch of knapweed, is very useful in keeping flying insects together while giving them "natural" conditions. Another simpler release cage is constructed from plastic milk jugs (Fig. 55) used for seedhead flies and moths. The cover over the jug keeps the seedheads dry; newly emerged adults can escape through the hole under the handle, and seeds are not released into the environment (the jug, with seeds, can be removed later).

Figure 54. Screen tent cage in which to release and contain knapweed bioagents

Figure 55. Milk jug release cage for knapweed bioagents.

Retaining Voucher Specimens

Retain 5 to 10 living or dead bioagents. Put the bioagents in a small vial with 70 percent ethyl alcohol for a voucher specimen. On a piece of white paper, in pencil (always use a pencil because alcohol will dissolve and bleed ink from pens and markers), write the name of the bioagent, source of the bioagent, the date of release, person or agency releasing, and release site. Put inside the vial. This identifies the bioagent released for future reference. Save several specimens for in-house records. Send the voucher specimens to your county extension educator or weed biocontrol expert.

Frequency of Release

Generally, if done correctly a single release will be sufficient to establish a bioagent population. More than one release might be needed if a prior release fails. It might take 2 years to determine if the release was successful.

Questions to Ask

• Are the bioagents already present at the site?
• Did the bioagents successfully establish following release?
• Are the bioagents found in high enough density to be collected and distributed?
• How far have bioagents dispersed from the initial release sites?
• Are the bioagents causing visible damage to the target weed?
• Are changes occurring within the plant community?

Answers to these questions will allow land managers to do the following:

• Determine the success of biological control efforts for target weed populations.
• Determine if a supplemental release is needed.
• Establish that biocontrol agents are impacting the target weed.
• Document changes in the plant community.

Releasing Multiple Bioagents

It is expected that bioagent populations will overlap and eventually sort themselves out naturally depending on the habitat, population density, and weed levels. As a rule, however, separate the species by at least 100 meters to allow your insect to establish without being impeded by another species.

Suggestions for Optimal Establishment

• A release of at least 200 bioagents.

• Releasing in the early morning hours between 6 and 10 a.m. or in the cooler evening hours between 7 and 8 p.m. is recommended. Bioagents are less likely to fly away immediately when released in cool temperatures.

• Avoid releasing bioagents during rainy or very hot weather for optimal establishment. However, sometimes it may be necessary to release in the rain.

• Releasing weevil bioagents at the bottom of a hill may encourage them to follow the phenological progression of the knapweed uphill, which may possibly increase the rate of spread; however, there is no data to support this observation.

• Common sense and care is a major factor in the survival and establishment of the insects.

5. Monitoring

Monitoring is an activity that tracks changes in the population that you are observing or measuring. In biocontrol, it involves monitoring bioagents (insects) or vegetation at the study site. Monitoring is conducted to: 1) ensure that the bioagents have established, 2) determine of the bioagents have spread from the release site, and 3) assess the impact of the bioagents on the target knapweed. Review the box, Questions to Ask (previous page), to determine your monitoring objectives.

Monitoring Bioagents

There are many methods used to monitor insects, including:

• Visual observations along a transect to count adults
• Sweep net sampling to count adults
• Using black light to capture and count nocturnal adult moths
• Use of pheromone traps to capture adult male Agapeta zoegana moths
• Dissecting roots and seedheads to observe larvae.

Outline your objectives before you begin monitoring (see Appendix C).

When to Begin Monitoring

Some bioagents may be detected as early as 1 year following release.

Some bioagents take 2 to 3 years to be detectable. Thus, if no bioagents are detected a year after the release, it does not mean that the insects failed to establish. Revisit the site for three years. If no evidence of insects is seen, either choose another site or make additional releases (see Appendix A). Consult with your county extension educator or local biocontrol of weeds expert.

Monitoring Methods

The monitoring method you choose depends on the:

• Life stage of the insect
• Amount of time available
• Expertise of the observer
• Availability of equipment
• Monitoring objective

For example, to merely determine if bioagents are established at the release site, observing any life stage is adequate. To determine the density of insects at the release site (i.e., number of insects per root), more detailed and intensive monitoring is needed. Likewise, if you want to know how far the bioagents have spread from the release site, a more systematic monitoring method is needed.

Additional Monitoring Methods

It is usually necessary to collect bioagents in order to monitor their population and activity. Insect monitoring uses the same methods used to collect bioagents for release. Additional monitoring methods including pheromone trapping, manual counting, and dissecting roots, are discussed below.

A Method for Sampling Plants to Evaluate Feeding Damage

Collect six plants along each of four lines in four cardinal directions (N, S, E, W) from the permanent location marker, for a total of 24 plants. Heads can be dissected indoors to see if they contain bioagent larvae or pupae. When sampling roots, dig one root at a time and slice it lengthwise to expose the center.

Monitoring Vegetation

Vegetation monitoring is conducted to describe and measure changes in the knapweed population following the release of bioagents. It consists of taking multiple measurements of a variable, such as plant height, density or number of seedheads. Analysis is performed to determine if changes in the weed infestation have occurred. The type of vegetation monitoring to use depends on the type of site (e.g., study or nursery site), availability of resources, and your monitoring objective.

Monitoring can be as simple as before-and-after photos, or counting seeds left in seedheads, or as intensive as conducting field studies for accurate and detailed assessment over time. The level of intensity used in monitoring should be dictated by the questions you want to address and the level of precision you need in the answer. In general, the simpler the monitoring method, the greater the likelihood of obtaining consistent and useful information. Develop a plan for collecting data based on the monitoring objectives. Use the "Monitoring Plan Questionnaire" (see Appendix C) to determine the objective or purpose of monitoring.

Two types of monitoring are qualitative and quantitative.

Qualitative monitoring

Qualitative monitoring uses descriptive elements about knapweed at the management site. It includes such general recording of presence or absence of bioagents, estimates of density, age and distribution classes, infestation mapping, and permanent photo points. Qualitative monitoring tends to be quick and inexpensive, and provides some insight into the status or change of the knapweed population. Its descriptive nature does not allow for detailed statistical analysis. Data obtained in qualitative monitoring may trigger more intensive monitoring later on. In addition, interpretations derived from this type of monitoring are often subjective.

Quantitative monitoring

The purpose of quantitative monitoring is to record and measure changes in the knapweed population after release of the bioagents. Quantitative monitoring can be as simple as counting the number of flowering knapweed plants in an area, or as detailed as measuring plant height (Fig. 58), seed production, rosette diameter and density, biomass, or plant community diversity. The data can be statistically analyzed and generally give precise information on population or community changes. In quantitative monitoring, sampling is more detailed than in qualitative monitoring (e.g., plant height, rosette diameter, number and size of seedheads, percent cover, species diversity). Quantitative monitoring takes more time to plan and implement, making it more expensive. It may also require specialized skills and training.

Figure 58. Measuring knapweed height at a quantitative monitoring site.

A suggested format for qualitative and quantitative monitoring:

• Choose location to monitor. Begin monitoring where the bioagents were first released since this is where the highest density agents is likely to occur and therefore where changes to the knapweed are more likely to be detected.

• Schedule monitoring activities. Schedule monitoring activities at the same time each year to be consistent and compare year-to-year variation.

• Determine a photo point. Establish a permanent photo point in the monitoring area. The photo point is an area where estimated cover and/or density classes of the knapweed can be recorded. Be sure to label the photo point. Create a photo record beginning at the time of bioagent release and at 2-year intervals thereafter (called before-and-after photos). Trends and changes in the knapweed infestation and the plant community over time can be visually assessed with photographs.

• Plan. This step involves knowing what and how much data to collect before starting. Consult an experienced field technician, researcher or statistician for guidance on the design of your monitoring plan. The types of variables usually measured are one or more of the following:

  • Visual estimates (qualitative). Record visual estimates of canopy cover. Determine the density and distribution classes of knapweeds at the release site at 1- or 2-year intervals (distribution classes are seedlings, rosettes, bolted and mature). Fill out a qualitative monitoring report (see Appendix E). Personnel may have to be trained in estimating general vegetation attributes.

  • Counts (quantitative). Count the number of seedlings, rosettes, seedheads, flowering knapweed plants within the quadrat. Seeds can be counted from a sub-sample of heads (about 30 heads) within the quadrat.

  • Measurements (quantitative). Measure plant height, stem diameter, plant circumference, etc.

• Choose a monitoring method. Choice of a monitoring method depends on the amount of time available to conduct the work and the monitoring objectives. Two methods of quantitative monitoring are transects and macroplots.

  • Transect. A transect is a straight line measured on the ground along which vegetation is sampled. Transect lines can be as long as 300 feet (100 m) or as short as 30 feet (10 m). Vegetation along the transect is sampled or measured using a quadrat placed at regular intervals along the transect (i.e., every 10 feet (3.2 m). While transects are a more systematic method of sampling vegetation, the location of the transect can be random. Transects are faster and easier to set up and use than macroplots (see Appendix F).

  • Macroplot. The purpose of the macroplot is to define a large area (e.g., 4 acres [1.6 hectares]) within which randomly placed small quadrats (1 sq. yd or 1 sq. m) are used to sample vegetation (see Appendix G). Although the macroplot is very useful and allows for sampling over a large area, it can cause considerable trampling by people at the site during sampling.

Establishing a Photo Point

Photographs of the release site are a valuable assessment tool. Visual evidence of vegetation change over time is derived from comparing pictures of the same site taken from the same location, at the same time of year, with the same horizon, and taken over a period of years. Records consisting of photographs are a qualitative form of monitoring and can be used in conjunction with more intensive quantitative monitoring techniques.

• Take baseline photographs at the time of the release. Choose the time of year to take the first set of pictures; flowering stages are ideal because of the contrasts with the surrounding vegetation. Once a year is sufficient but it is good practice to frequently take pictures of the site.

• Locate a photo point. The location of the photo point is determined at the time of establishing the release site. Note and document the location of the photo point marker in case of need to relocate it later. When photographing the site, point your camera so as to include the permanent marker location in the scene.

• Close-up pictures. Close up pictures are useful to show the amount of ground covered by vegetation and litter. A square frame, 3 feet x 3 feet, is recommended. Frames can be made of PVC pipe, steel rods, rebar, etc. Drive brightly painted angle iron stakes into the corners to permanently establish the plot. Repaint the stakes each time photos are taken. Put a plot identification label on the ground next to the frame. The camera point should be on the north side of the photo, so that pictures can be taken at any time of the day without a shadow.

• General view pictures. General view pictures give a broad view of the release site and the surrounding landscape.

  • Establish the point approximately 100 feet from the permanent location marker.

  • Choose an angle that will best show changes in the knapweed infestation over time.

  • Include a photo identification label, a general view of the site, some sky, and a reference point in the foreground (fence post, shrub, or person), and a distinct landmark on the skyline.

  • Use photos taken the previous year as reference for the following year’s photos.

Supplies Needed

• Camera (35 mm or digital)
• Color film (if 35 mm)
• Notebook and forms
• Metal or wooden stake for camera point
• Bright spray paint
• Previous year's photo

[  Contents  ]   [  Previous  ]   [  Next  ]