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Project description

Ecological approaches for management of artichoke thistle (Cynara cardunculus) spread. (01XN016)
Program Exotic Pests and Diseases Research Program
Principal
investigator
J.S. Holt, Botany and Plant Sciences, UC Riverside
Host/habitat Grassland; Rangeland
Pest Artichoke Thistle Cynara cardunculus
Discipline Weed Science
Review
panel
Natural Systems
Start year (duration)  2001 (Three Years)
Objectives Use completed data to construct a phenological model to predict the onset of vegetative growth and flowering following dormancy in artichoke thistle and validate the model over one growing season in coastal grasslands.

Conduct experiments on control of artichoke thistle sprouting by burning, mechanical control and chemical control in order to develop effective management techniques.

Combine data from Objectives 1 and 2 to initiate practical experiments on timing and methods of preventing and managing artichoke thistle re-growth and seed production and work with land managers to monitor experiments over a growing season.

Final report This project tested the utility of degree-day models, widely used in agricultural systems, to predict phenology (timing of development) of Cynara cardunculus, artichoke thistle, in a California grassland. Experimental data on artichoke thistle phenology, temperature data from CIMIS (California Irrigation Management Information System) stations close to field research sites, and programs available on the UC IPM Web site were used to construct the degree-day models.

Field experiments were conducted during 2002-03 and 2003-04 in Crystal Cove State Park in Orange County, Calif. to validate the models for practical use by comparing observed to predicted phenology determined by the degree-day models. The model with temperature cutoffs of 10 C and 20 C using a vertical cutoff method best predicted seedling emergence and production of two leaves.

Based on this success, models to predict resprouting, bolting, and flowering of artichoke thistle are under construction. In spring 2003, an experiment was conducted at UC Riverside to test the effectiveness of burning, clipping, and a herbicide (Roundup) for control of mature artichoke thistle plants. In spring 2004, an experiment was conducted on plants that had been clipped at ground level in fall 2003 to evaluate the effectiveness of two herbicides (Roundup and transline) applied at different phenological stages of regrowth (early resprouting, late resprouting, bolting, and flowering).

In the first experiment, burning and clipping stimulated greater resprouting while application of Roundup reduced resprouting relative to untreated plants. In the second experiment, both herbicides were most effective in controlling plants at the late resprouting stage (100% mortality) and least effective at the flowering stage (48% mortality). By combining phenological models with information on control of artichoke thistle, land managers will be able to use available temperature data to choose and schedule management techniques for more effective control of this invasive weed.

Third-year
progress
Research to develop a predictive model of artichoke thistle phenology is continuing for a third season at Crystal Cove State Park near Laguna Beach, California, in artichoke thistle-invaded grasslands. From January to August of 2002, 2003, and continuing in 2004, six permanent transects were visited weekly to record development of 240 plants that began the growing season at one of four growth stages (seedling, juvenile, immature rosette, and mature rosette). Data were recorded on emergence or sprouting, number of leaves, onset of bolting, and onset of senescence throughout the growing season. These data have been used to validate a degree-day model to predict the timing of emergence of artichoke thistle. Following the 2004 season, models will be tested for sprouting, flowering, and senescence. Artichoke thistle was planted at the UCR Citrus Experiment Station in February 2002, and allowed to grow for two seasons. In summer 2003, experiments were conducted to test the effectiveness of burning, clipping, and herbicides for control of mature plants. In spring 2004, we initiated experiments at UCR on plants that had been clipped off at ground level in fall 2003 to evaluate the effectiveness of two herbicides applied at different phenological stages of regrowth. We will combine the phenological models with results of the control experiments to recommend the optimal timing and method of artichoke thistle control in grasslands. This approach will allow land managers to use available temperature data to plan management techniques for more effective control of artichoke thistle.

Second-year
progress
Research to develop a predictive model of artichoke thistle phenology (Objective 1) is continuing for a second season at Crystal Cove State Park near Laguna Beach, California, in artichoke thistle-invaded grasslands. In winter of 2002 we established three 50-meter transects on a north-facing hill and three on a south-facing hill. At ten random points along each transect, the nearest plant at each growth stage was marked (seedling, juvenile, immature rosette, and mature rosette) for a total of 240 plants. Data were recorded on emergence or sprouting, number of leaves, onset of bolting, and onset of senescence. In winter of 2003, 240 new plants were marked and measured to obtain a second season of data. Since 2001-02 was an extreme drought year, the experiment will be continued in 2003-04 to obtain another season of data. This data will be used to validate a degree-day model to predict the timing of emergence, sprouting, flowering, and senescence of artichoke thistle. For Objective 2, we planted artichoke thistle at the UCR Citrus Experiment Station in February 2002 and allowed it to grow for two seasons. In summer 2003 we will conduct experiments to test the effectiveness of burning, clipping, and herbicides for artichoke thistle control. We will combine the phenological model with results of the control experiments to test the timing and method of artichoke thistle control in grasslands (Objective 3). This approach will allow land managers to use available temperature data to plan management techniques for more effective control of artichoke thistle.

First-year
progress
Research on Objective (1) is under way at Crystal Cove State Park near Laguna Beach, California, in artichoke thistle-invaded grasslands. In winter of 2002 we established three 50-meter transects in each of two artichoke thistle populations, one on a north-facing hill and one on a south-facing hill. At ten random points along each transect, the nearest plant at each of four growth stages was marked (seedling, juvenile, immature rosette, and mature rosette) for a total of 40 plants per transect and 240 plants total. Data are being recorded on number of leaves, onset of bolting, and onset of senescence and dormancy. Measurements will continue through August, when leaves typically senesce and plants enter dormancy; measurements will resume in fall of 2002 when re-sprouting resumes. Temperature and soil moisture are also being monitored at five locations in each population. This data will be used to validate a model to predict the timing of sprouting and flowering of artichoke thistle using a degree-day approach. Such a model would allow land managers to use readily available temperature data to time the application of management techniques for more effective control of artichoke thistle. We will also conduct experiments to test the effectiveness of burning, clipping, and herbicide application for control of artichoke thistle. By combining the predictive model and the results of the control experiments, we will be able to develop a specific management plan for control of artichoke thistle in the field.

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