B A C K C O U N T R Y. Bio-Control of Diffuse Knapweed

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1 Highlands Ranch Community Association B A C K C O U N T R Y W I L D E R N E S S A R E A Bio-Control of Diffuse Knapweed The Highlands Ranch Community Association Highlands Ranch is a 22,000 acre master planned community located approximately 12 miles southwest of Denver in Douglas County, Colorado. Highlands Ranch is one of the country s largest mixed use master planned communities. The first homes in Highlands Ranch were built in The Highlands Ranch Community Association (HRCA) is the master association of Highlands Ranch and is one of the largest in the country with a current population of 90,000 with approximately 32,000 dwelling units. Highlands Ranch is zoned for over 36,000 dwelling units. The HRCA s mission is to enhance property values within Highlands Ranch and create quality of life through recreation, community events, and leadership. The HRCA operates four state of the art recreation centers with a total of 329,685 square feet of indoor recreation space. The recreation centers are open 361 days of the year and welcomed about 1.8 million visitors in The HRCA also directs over 100 community events throughout the year and oversees administrative functions such as billing and covenant control. See Highlands Ranch page 2. Volume 1, Issue 1 April 2007 The Highlands Ranch Community Association Finds a Partner in Conservation - Bugs One million acres, or 1500 square miles of land in Colorado have been invaded by aliens; aliens of the plant variety. Non-native weeds that do not belong in our ecosystem have established themselves in Colorado and throughout the United States. They have earned the name noxious weeds because they are invasive, aggressive and they spread quickly. The noxious weeds often overtake native plants and can render huge tracts of land useless to wildlife and agriculture. In Colorado alone, noxious weeds have cost residents $10 million annually in lost productivity (Colorado State Cooperative Extension). Along the Front Range in Colorado, diffuse knapweed has taken a strong hold. A 2002 survey conducted by the Colorado Department of Agriculture found 145,148 acres infested by knapweed. Diffuse knapweed is an opportunistic weed that often invades disturbed areas and once established will create a monoculture and displace most native plants and grasses. Knapweed spreads extremely fast as one single plant can produce up to 18,000 seeds (Figure 1). Land infested with knapweed has very little value for wildlife habitat or agricultural uses. Figure 1 A typical knapweed plant. The light brown, bulbous parts of the plant are the many seed heads. Each seed head can produce anywhere from 4-20 seeds. This single plant has 100 s of seed heads and would easily produce thousands of seeds. There are several methods to control knapweed. Cultural control encourages cultivation of native plants to compete with knapweed, mechanical control includes mowing the knapweed to prevent the plant from producing seeds, and chemical control involves the use of herbicides to kill the knapweed. In 1997 Professor Tim Seastedt of the University of Colorado at Boulder was one of the first along the Front Range to seriously study an often overlooked way to control knapweed: Biocontrol. Biocontrol, in this case, is the introduction of non-native insects to control knapweed. The introduced insects are natural enemies of knapweed in its homeland of Eurasia. The insects involved had been approved for release by the Colorado Department of Agriculture several years before 1997, after it was determined that they would not effect native plants. By 2001 Seastedt s research showed that the introduced insects were experiencing great success in controlling knapweed. In 2002 the Highlands Ranch Community Association (HRCA) approached Shea Homes about the possibility of releasing these insects in the Backcountry Wilderness Area of Highlands Ranch. The

2 Page 2 The Highlands Ranch Community Association Continued from page 1 With 61 percent of Highlands Ranch devoted to non-urban uses, including open space and recreation, the Highlands Ranch homeowners place a high value on open space conservation. The jewel of conservation in Highlands Ranch is the Backcountry Wilderness Area; an 8,200 acre (over 37% of Highlands Ranch) conservation area in the southern section of Highlands Ranch. The Backcountry is one of the largest conservation areas along the Front Range from Denver to Colorado Springs. The mosaic of habitats including grasslands, shrubs, and ponderosa pines boasts a herd of elk, plentiful mule deer, pronghorn, mountain lion, coyotes, hawks, eagles, and is an operating, historic cattle ranch. Shea Homes (see more on Shea Homes on the next page) will convey the Backcountry to the HRCA in the next few years. The HRCA and Shea Homes completed an early conveyance of 874 acres of the Backcountry in The HRCA constructed over 6 miles of natural surface trails through the 874 acre natural area; providing HRCA residents with yet another terrific and unique amenity. Wildlife viewing, hiking, mountain biking, and trail running are now available right in our backyard. Backcountry Wilderness Area is an 8,200 acre conservation areaas well as a historic and current cattle ranch that is teeming with wildlife and currently owned by Shea Homes, the developer of Highlands Ranch. The Backcountry will eventually be conveyed to the HRCA once Highlands Ranch approaches build out. The knapweed infestation in the Backcountry was relatively light, but left unchecked, would eventually explode into a very serious and very expensive problem. The plan that the HRCA submitted to Shea was to collect the insects from Professor Seastedt s research area near Boulder and release them in certain areas of the Backcountry. The HRCA also planned to compliment Seastedt s research by duplicating his research in the Backcountry in order to provide further documentation of the insects success in controlling knapweed. In July 2002 the HRCA and Shea Homes released two different kinds of insects that would begin to attack the knapweed. Over 3,000 seed head weevils (Figure 2) and 155 root boring weevils (Figure 2) Figure 2 Left, the seed head weevil (Larinus minutus). Right, the root boring weevil (Cyphocleonus achates). One of the reasons knapweed is so successful in establishing large populations and spreading quickly is it produces enormous amounts of seeds. Figure 1 shows a typical knapweed plant and the many seed heads one plant can produce. A typical knapweed infestation can easily produce a few thousand seeds per square meter; and often much more. The seed head weevil attacks the seed production of knapweed. The adult weevil burrows into the seed head where it lays its eggs. The larvae use the seed head as a womb and feed on the seeds as they develop. Four weeks later the larvae emerge from the seed heads as an adult, and the seed head is barren of seeds (Figure 3). Figure 3 A seed head weevil emerges from the knapweed seed head. It takes about 4 weeks for the larvae to consume all of the seeds in the seed head and emerge as a new adult. Figure 4 Evidence of the root boring weevil. The vital tap root on this knapweed plant has been severely weakened by the larvae of the root boring weevil. The root boring weevil attacks the health and vigor of knapweed by attacking its root system. The adult weevil lays its eggs on the root, just beneath the soil. When the larvae hatch, they burrow into the root and feed on the root, weakening the plant (Figure 4). A knapweed plant infested with the root boring weevil is stunted and produces fewer seed heads. The weevil also makes it easier for bacteria and fungi to attack the root system which usually ends up killing the plant.

3 Figure 5 shows the release site in 2002, when the first insects were released. The release site measures 100 meters by 30 meters. This site was chosen as the release site because it was a disturbed site where knapweed had taken over and there was very little native grasses or forbs competing with the knapweed. Fig. 5 Release site at the time of the initial insect release in The white flowers of knapweed are apparent. Very little native vegetation is competing with the knapweed. Along with the release site, two other sites were monitored; control 1 and control 2. Control 1 was adjacent and parallel to the release site with a 20 meter gap in between the two sites. However, it was not a disturbed area and the native grasses and forbs were still very much in control. This site was chosen to monitor the spread of knapweed; and would later be valuable to examine the natural dispersal of the insects. Control site 2 is.6 miles west of the release site. This site was chosen because it had an established knapweed infestation comparable to the release site infestation and would be relatively unaffected by the insect release; at least during the term of the study (Figure 6). Control Area 2.6 miles Release Area Control Area 1 Fig. 6 Location of the release site, control site 1, and control site 2. Table 1 shows the average stems of knapweed per square meter for the 5 year period beginning in Stem density is measured by taking numerous random samples of one square meter sections and counting each stem within the square meter (Figure 7). Notice the release site in 2002 had a relatively high stems per square meter while control site 1 had a low stems per square meter. As mentioned before, control site 1 was not a disturbed site and had good cover with native plants. The knapweed was just beginning to move from the release site into control site 1 in Shea Homes For well over a century, the Shea family companies have been building their legacy of caring for the customer. Shea s history includes work on world renowned projects such as the Golden Gate Bridge and the Hoover Dam. More recently, Shea Homes has earned the reputation of being one of the nation s premier developers and home builders. Since 1968, Shea Homes has built homes and communities for over 52,000 families. The success of Highlands Ranch is due in large part to the progressive thinking and excellent planning by Shea Homes. The Highlands Ranch master plan calls for 61 percent of the land to be devoted to non-urban uses including open space and recreation, 31 percent to residential uses, and eight percent to business properties. According to Shea Homes Vice President of Planning Steve Ormiston, open space preservation and its management has always been an integral part of the plans for Highlands Ranch. The 8200-acre Backcountry Wilderness Area along with over 4200-acres of additional public open space represents one of the largest open space areas in the Denver Metro area protected for future generations. The early planners of Highlands Ranch had exceptional foresight to set aside 8,200 acres of open space now called the Backcountry Wilderness Area of Highlands Ranch. See Shea page 4

4 Table 1 The average number of knapweed stems, , for each area. Shea Homes Continued from page 3 Shea Homes cares for and manages the Backcountry; but will eventually convey the property to the HRCA. The progressive thinking of Shea Homes played a significant role in the use of Biocontrol insects to help control knapweed in the Backcountry Wilderness Area of Highlands Ranch. When the HRCA approached Shea Homes about using the insects to control knapweed, the insects use was not common place, and documented successes were even rarer. However, Shea Homes recognized the potential benefits, embraced the opportunity, and allowed the HRCA to release the insects. The end result was control of the knapweed, saving Shea Homes and eventually the HRCA thousands of dollars in the cost of herbicides and other control methods; while improving the habitat for the array of wildlife that call the Backcountry Wilderness Area home. Highlands Ranch is truly fortunate to have such a forward thinking master developer in Shea Homes. In 2003 and 2004, the knapweed infestations in all of the sites saw small, insignificant declines. These small fluctuations are most likely a normal cycle. Knapweed seeds are viable in the soil for many years. The seeds can wait out dry years and germinate when conditions are better. It appears that 2005 was one of those years where the conditions were ripe, and the knapweed rose to its highest density in all three of the areas. The infestation in control site 1 was now as bad as it was in the release site; evidence of knapweeds ability to spread to new areas in a short amount of time. However, there was also something else happening in 2005 that was of considerable importance. When the seed head weevil and the root boring weevil were released in 2002, the population of seed head weevils steadily increased while the root boring weevil literally disappeared in 2003 and There were only a few sightings of the root boring weevil in 2003 and zero sightings of it in In 2005 however, the root boring weevil population, along with the seed head weevil population, exploded. Field observations in 2005 revealed that most knapweed plants had 3-10 seed head weevils and at least one root boring weevil (Figure 8).The population growth of both insects was drastic in the fourth year of the study. Now the question was what effect, if any, would this have on the knapweed? Fig. 7 Sampling the release site to attain the number of stems per square meter. Each site was sampled 40 times, in random locations, to get the average number of knapweed stems per square meter.

5 In 2006, the effects of the insects dramatic population explosion was obvious. As you can see in Table 1, the 2006 stem densities plummeted in both the release area and control site 1; immediately adjacent to the release area. The insects appeared to have the desired effects, knapweed was in serious decline. Figure 9 shows the release area in 2005 when the knapweed infestation was at its worst. Figure 10 shows the release area in 2006, when knapweed was virtually wiped out. The cattle ranching operation and wildlife on our property will benefit from this proactive solution to noxious weed problems. Land managers everywhere should be encouraged to think outside the box; we need to be good stewards and balance our approaches to range management. Fig. 8 This was a typical sight in 2005, several of each insect on most knapweed plants. Fig. 9 Above, the release area in 2005, the area was completely covered by knapweed. Gary Debus, HRCA Community Manager

6 Fig The release area in 2006, the majority of the knapweed is gone and the native grasses are coming back. The same Ponderosa Pine is visible in the upper left corner of the photos. In the coming years, the sites will be monitored in order to determine if the insects offer long term control, and if the insects are efficient enough dispersers to seek out other knapweed infestations on their own. Our initial field observations indicate that the seed head weevil disperses very well on its own since it is able to fly, but the root boring weevil is not a flyer and may have a tougher time dispersing. There are plenty of questions yet to be answered; but these results provide evidence that biological control of knapweed with these two insects is a promising possibility; and at the very least, a useful tool in the fight against knapweed. For additional information: (Click on Backcountry Wilderness Area)