   Sweet Resinbush Invading Cottonwood - February 21, 2001 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Sweet resinbush (Euryops subcarnosus), a South African native, is spreading across the landscape near Verde Village south of Cottonwood. This plant was introduced to Arizona in the 1930's in the hope that it would produce forage for livestock and protect soils from erosion. Instead, it has steadily expanded its range displacing native forage plants that wildlife and livestock depend upon. Sweet resinbush is a medium-sized shrub to three feet tall. It has small leaves that are divided into three to five narrow lobes. Sweet resinbush has foliage in winter and spring, then sheds its leaves during the dry season. It is a member of the sunflower family and has yellow, daisy-like flowers during January and February. The flowers produce an abundant seed crop by April or May. The seeds form in star-like clusters of about ten fruits. Most of the seeds drop to the ground around the parent plant. In the Cottonwood sweet resinbush infestation, many seedlings can be found both near established plants and several yards away. These fruits are covered with fine "hairs" that allow them to cling to animal fur and clothing. This creates a great potential for seed transport and establishment of new populations. Interestingly, sweet resinbush is not palatable to any domestic or wild grazing animals. This misconception came from a 1928 publication: The Flowering Plants of South Africa, Vol. III, by I.B. Pole Evans. In this publication, it misstated that the plant was palatable. This misinformation attracted the attention of USDA scientists looking for plants to improve the range and, as they say, the rest is history. Recent research has shown that most species of Euryops contain noxious chemicals, which render them not only unpalatable, but also toxic to wildlife and livestock. All one needs to do is smell the foliage and flowers of sweet resinbush and a pungent, resinous aroma is apparent. The largest infestation of sweet resinbush in Arizona is at Frye Mesa near Safford. Records indicate that 12 potted plants were planted in the area in 1935. In 1970, the population had spread about 10 acres and not considered a problem at that time. Today, sweet resinbush plants are found 6½ miles downslope from the original site and the infestation covers 3,000 acres (5.4 square miles). Aside from Frye Mesa, there are seven other known sweet resinbush populations in Arizona. Between 1970 and now, the Frye Mesa sweet resinbush population expanded its range 300 times. This is a vivid example of what could happen in Cottonwood. There is a tremendous potential for this plant to spread throughout the surrounding lands and downward through the watershed. The Cottonwood sweet resinbush population is on U.S. Forest Service and privately owned land. Noxious weeds become a real challenge to control once they invade a subdivision. Another concern associated with many noxious weed species is their ability to form a monoculture and exclude native plants. Sweet resinbush does appear to form a monoculture. It is not known whether this is due to the chemical compounds they contain (allelopathy) or a greater competitive advantage that allows it to better exploit resources (especially soil water). In any case, there are several areas in the Cottonwood population where large areas of bare ground are present near well-established sweet resinbush individuals are growing. The U.S. Forest Service Verde Ranger District is currently gathering public input to control/eradicate the sweet resinbush in the Cottonwood area. This is the first step of the Environmental Analysis process. After collecting and reviewing public input, the Forest Service will create various alternatives and present them to the public. The public will then have the opportunity to review and comment on these alternatives before a final decision is implemented. In 1999, the Forest Service tried to burn the sweet resinbush population. The burn was not successful due to the lack of fuels to carry the fire. The proposed action this year is to use an Integrated Vegetation Management (IVM) approach. IVM uses a variety of techniques to increase control success. Mowing would be used to reduce plant size. Mowing would be followed by hand spraying of herbicide and hand digging. Mowing would also stress the plants and reduce the quantity of herbicide required to kill the plants. The herbicides they propose using would have negligible effects on non-target plants and animals. For more information, call Clare Hydock at the USFS Verde Ranger District at (928) 567-4121. The University of Arizona Cooperative Extension has publications and information on noxious weeds and their control. If you have gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. There are extensive noxious weed resources available through the Yavapai County Cooperative Extension web site is http://ag.arizona.edu/yavapai/anr/nr/. |