Location: Southern Horticultural Research2011 Annual Report
1a. Objectives (from AD-416)
The objective of this collaborative research is to evaluate soil incorporated insecticides for controlling strawberry rootworm (SRW), Paria fragariae, infestations in containerized evergreen azaleas.
1b. Approach (from AD-416)
SRW are an important insect pest of evergreen azaleas. SRW overwinter as adults in trash on the soil surface and within the potting media. Adult beetles emerge in early spring (Feb-Mar), mate, and begin laying eggs on the sepals of azaleas. Eggs hatch and larvae migrate into the blooms to feed and develop. Larvae are deposited to the soil surface as blooms are shed from the plants. Larvae move into the soil to either feed on the root system or to pupate, but inflict little damage on the plant at this point. The adults feed at night and cause small irregular shaped holes in the leaves which diminish the marketability of the plants when insects reach high numbers. Since these insects require soil contact in order to pupate and complete their transformation into adults, a soil applied insecticide would prevent further development and prohibit the formation of new adults. A soil incorporated insecticide would also prevent worker exposure to pesticide drift and lessen the impact on pollinators. Bifenthrin (trade name Talstar®) is currently used in containerized nursery stock as a preventative treatment for imported fire ant control, Solenopsis spp., in both spray and soil incorporated treatments. A rate of 25ppm AI of granular bifenthrin is considered effective to at repel fire ants for a certification period of one year. Ornamental nurseries that comply with these regulations are certified “fire ant free” under APHIS-PPQ guidelines. If granular bifenthrin at this rate or slightly higher rates was proven effective at controlling SRW populations in potted azaleas, this would negate need for further insecticide treatments and offer a preventative for eliminating newly developing SRW in the potting substrate. This research will evaluate the effect of increased dosage of granular bifenthrin on SRW populations in a nursery setting. This study will be installed at three locations: Rocky Creek Nursery in Lucedale, MS, the Mobile Ornamental Horticulture Research Station in Mobile, AL, and the USDA-ARS Thad Cochran Southern Horticultural Laboratory in Poplarville, MS. At each location two blocks will be installed in order to account for possible site variation. Each block will consist of a randomized configuration of 40 potted azaleas (4 treatments, 10 reps per treatment). The cultivar ‘Pink Ruffle’, which shows susceptibility to SRW damage, will be used exclusively. One gallon ‘Pink Ruffle’ azaleas will be transplanted into three gallon containers that will contain potting media with 25, 50, and 75ppm of bifenthrin incorporated into the potting media. These concentrations were achieved taking bulk density of the potting media into consideration using formulae provided in the 2007 USDA APHIS-PPQ imported fire ant guidelines for quarantine treatments for nursery stock (USDA-APHIS program aid No. 1904). Controls will consist of untreated pine bark potting media. Each block will be evaluated every 30 days for a period of one year. At each evaluation period, a rating of plant damage due to SRW and counts of any SRW found present will be recorded. This data will be compiled and analyzed using basic ANOVA procedures using a repeated measures design.
3. Progress Report
The pyrethroid drench, bifenthrin (Talstar), was applied to soil of potted azalea plants as a chemical control for strawberry rootworm (SRW), Paria fragariae. Drenches however proved ineffective for SRW control. Concentrations of 25ppm (recommended), 50ppm, or 75ppm failed to kill or immobilize SRW larvae, despite the product’s long half-life of 6 months. Populations of SRW were lower than expected during our trials and perhaps a more severe outbreak may have been brought under control by the Talstar drenches. Findings from a subsequent monitoring program for adult SRW however indicate control for strawberry rootworm is probably best achieved with well-timed aerial applications of registered insecticides. Weatherproof monitoring stations for adult leaf beetles including SRW reduced nursery’s insecticide costs by $2500 in the spring of 2011, which resulted in additional plant sales totaling $10,500. The ADODR or designated representative met regularly with the cooperating scientist, and these meetings included site visits.