- Additional Plants: native plants, ornamentals
- Education and Training: extension, on-farm/ranch research, workshop
- Pest Management: biological control, field monitoring/scouting, integrated pest management, weather monitoring
Urban forestry, communities, and businesses rely heavily on the green industry to supply quality ornamental trees, shrubs, flowers and bedding plants for the green space around businesses, parks and homes. Nurseries and greenhouse operations grew many of these plants and contributed nearly $19 billion in value-added impacts to the economy in 2002 (Hall et al. 2006). These businesses grow or maintain plants following pest management programs to keep insects and diseases under control. Redheaded flea beetles are polyphagous insect pests capable of causing enough damage to render plants unsalable. Nurserymen have limited opportunity to use integrated pest management against redheaded flea beetles because so little is known about their biology. The goal of proposed project is to provide growers with additional management options by 1) developing degree-day and plant phenological prediction models, 2) training growers how to scout for larvae and 3) using entomopathogenic nematodes for the soil-dwelling larval stages. Research focused on the beetle’s biology addresses a priority established by both the National IPM Roadmap and the American Society of Horticulture – improving pest management strategies for insects. Incorporation of biological control into management efforts will contribute to reducing environmental risk and improve worker safety by reducing the amount of insecticides used to control the pest. Project results willed be shared with nurserymen via publications and a fall workshop.
Project objectives from proposal:
Growing Degree Days and Plant Phenological Indicators
The project will collect data from a nursery in Maryland to monitor the activity of S. frontalis from spring through summer. Temperatures of ambient air, soil, and soilless potting media in containers will be recorded with Hobo® data loggers (Onset Computer Corporation, Pocasset, MA). Ambient air temperatures will be compared against nearby weather stations operated by NOAA, the Delaware Environmental Observing System, or similar climate centers. Missing data values will be filled in by data from regional centers or averaged from days preceding and following the missing data point. The redheaded flea beetle overwinters as an egg; therefore, the first evidence of infestation is when the adult emerges. Nursery containers will be inspected early in the spring for larval and adult activity and correlated with recorded soil, potting media and air temperatures to calculate the GDD. The larval data will provide nursery managers an opportunity to control beetle populations with EPNs before the emergence of adults, the damaging stage of this insect. Soil temperatures may be different than the potting media in containers; thus larvae found in the ground may develop differently, thereby a potential source for staggered adult emergence in the spring.
Our goal is to create a simple predictive model for nurserymen to use on a regular basis. We will start recording daily temperatures on March 1. The ‘average method’ is the procedure we will follow in use in calculating the growing degree-days below:
GDDi = [(Tmax+Tmin)/2]- Tbase,
where GDDi is the accumulated growing degree-days on day I, Tmax and Tmin are the maximum and minimum daily temperatures, respectively, Tbase is the baseline temperature. The baseline developmental temperature for S. frontalis, like many ornamental insect pests, is not known and a common baseline temperature used is 50°F (10°C; Herms 2004). Developmental thresholds for other flea beetles are reported between 7.5°C to 9.3°C depending on the flea beetle species (Skinner et al. 2006, Pettis and Braman 2007). Skinner et al. (2006) cautions regional differences may affect the accuracy of the predictive models and should be considered before generalizations are made. The developmental threshold and corresponding predictive growing degree-days of 9.3°C (48.7°F) developed for Aphthona nigriscutis, a specialized flea beetle on leafy spurge and Altica litigata will be used as a guideline to predict S. frontalis activity. The research on other flea beetles at this temperature suggests 237 to 670 growing degree-days for adult emergence (Skinner et al. 2006, Pettis and Braman 2007). We will also use base temperatures of 10°C (50°F) and 7.2°C (45°F) at the different locations to obtain an average number of growing degree-days when adults or larvae are active. Data will be gathered to determine larval activity, adult emergence, duration of peak adult activity and subsequent generations. The models for the three temperatures will be averaged and analyzed for accuracy in predicting spring adult emergence by comparing actual and predicted Julian dates. A goodness-of-fit analysis will be conducted and the best model used in future years to predict pest activity.
Record plant phenology of nearby plants to use as indicators:
Cooperators at the nursery will observe plants to record phenological plant stages such as: flower bud break, leaf bud break, bloom, full bloom and petal fall when flea beetle larvae or adults are active. Plants classified as in ‘bloom’ will be when the first flower has opened; whereas, plants listed as ‘full bloom’ will have the majority (>50) of the flower buds open and expanded. Plant stages will be recorded from May until August and correlated with the growing degree-days.
Emerging flea beetles will be observed and collected similar to Ulmer and Dosdall 2006. Bug-dorms® will be placed over common weeds, such as lamb’s-quarters (Chenopodium album), and container-grown production plants when larval activity is first detected. A collection vial will be attached in the center part of the cage and inspected for the presence of adult S. frontalis on each visit to document beetle densities. Battery-powered aspirators will be used to collect flea beetles found clinging to the sides of the cage. (Hausherr’s Machine Works, Toms River, NJ). To locate containers with beetle larvae, the entire plant and root ball will be removed from the container and the outside of the root mass inspected. This non-destructive sampling method for flea beetle presence was useful for collection of larvae in laboratory trials evaluating nematode efficacy. One or two larvae per root ball generally indicated an average of 8 larvae per 5 gallon container (Kunkel 2009, unpublished). Bug-dorms will confine three groups of weeds and three container-grown plants at each nursery until the adult flea beetles emerge.
Scouting for plants with existing flea beetle larvae infestations should focus on containers 13 L (3 gallons) or less because efficacy of field-applied nematodes is determined by destructively sampling the plants while searching through root balls. Twenty plants with three or more S. frontalis larvae found crawling on the root ball would be used in the trial. Nematode applications will be made in the evening to minimize the risk of nematodes death from UV exposure. Nematode concentrations will be 0.5 x 106/1 L of container and will be supplied by a distributor. Ten days post-application treated plants will be destructively sampled to determine flea beetle mortality. Two hundred grams of potting-media will be removed to evaluate the media for EPN viability in a laboratory experiment. A common baiting technique uses Galleria mellonella, an insect very susceptible to EPN infections, to determine if IJs are present in potting media. These samples will be placed into Petri dishes (15.0 cm dia.) and 10 G. mellonella larvae added. After 3 d, percent mortality of G. mellonella will be recorded and a fresh 10 wax worm larvae will be added. This baiting technique will continue every three days until there are no dead G. mellonella larvae (Booth et al. 2002). The total of dead wax worms will be tabulated per treatment and analyzed to determine if EPNs persisted throughout the experiment.
Information developed on the two predictive tools for pest activity, growing degree-days and plant phenological indicators will be correlated to vulnerable life stages of S. frontalis. A poster will be designed to illustrate these correlations for use by nurseries in the northeast and distributed in the fall. Techniques for scouting flea beetle larvae in nursery containers will be recorded and compiled into a video that will be posted on the internet at a blog-site hosted by the University of Delaware. The efficacy of EPNs versus S. frontalis larvae, the seasonal biology of the insect, and references to the links of videos will be compiled into a laminated fact sheet for distribution at the fall workshop. A postcard mailing to announce the fall workshop will be sent to a list of growers from the mid-Atlantic region and an additional mailing as a reminder closer to the set date. The workshop will discuss the overall importance of monitoring and scouting for insect and disease pests, the convenience of plant phenological indicators, and the role these IPM tactics played in incorporating biological control as a management option for the redheaded flea beetle, Systena frontalis. This beetle has become a nursery pest from New York to Alabama and west to Michigan; therefore, these fact sheets and a digital version of the poster would also be shared with colleagues in those regions. The cooperating nursery would be encouraged to share their experiences with fellow stakeholders at meetings or other business conversations when appropriate.