Using IPM Methods for Dealing with Major Insect Pests of Dahlias
In the spring of 2018, Nick Weber of the Maryland Dahlia Society asked us to develop an integrated pest management approach for dealing with insect and mite pests of dahlia plantings. Over the years we have developed many biological control programs for greenhouses crops with good success rates. We decided that a combination of systemic chemical and biological control releases could work well. Working closely with Nancy Rechcigl of Syngenta, Bell Nursery of Burtonsville, Jan Meneley of AgBio of Westminster, Colorado, and Koppert Company, we analyzed several products before settling on the use of Mainspring drenches applied twice during the year, combined with predacious mite releases, use of banker plants and predacious insects, and pheromone and food-baited sticky traps.
The first step was obtaining seed of an ornamental pepper called ‘Purple Flash’ from Ball International. We used this cultivar for its characteristic of continual blooming during the growing season. These peppers would be used as banker plants to produce pollen and nectar to feed a predacious bug called Orius, the minute pirate bug, which is used to control thrips. Bell Nursery started growing the plants for us in March. Pepper plants are slow to get going and we needed them in bloom by midsummer, so three months needed to be allotted to have them in bloom for our Maryland growing season.
The dahlia tubers were planted in late May at two sites in Maryland: Nick Weber’s Heritage Rosarium in Brookeville, and Crazy 4 Dahlias, John Spandenberg’s Damascus farm. We had treated blocks and conventional treated blocks of plants. On the treated blocks we made a soil drench of Mainspring at a rate of 8 oz. /100 gallons of water. Each plant was drenched at the base with 8 oz. (237 mL or .24 L) of prepared liquid solution.
Mainspring™ GNL is a suspension concentrate (SC) formulation containing 1.67 pounds of cyantraniliprole per gallon. Cyantraniliprole belongs to the anthranilic diamide chemical class, introducing a new class of chemistry in IRAC Group 28 to ornamental insect control. Mainspring quickly stops insect feeding after ingestion. It is compatible with many beneficial insects and mites.
This Mainspring application provided protection from aphids and thrips feeding on dahlia foliage and stems. The two common species of aphids found on dahlias are green peach aphid and melon aphid. Plants were monitored on a weekly basis, and no aphids were detected in the first 12 weeks of growth. Also, no thrips populations were found on treated plants.
We obtained Amblyseius cucumeris mites, a predatory mite that feeds on thrips nymphs, and has been used for prevention, control, and maintenance of various thrips species with fairly good success in greenhouses. The mites use sucking mouthparts to pierce and ingest contents of their prey. We purchased the mites under the name THRIPEX-PLUS from Koppert Biological Systems. For the first release we used mites in a loose grain container mix, sprinkled on dahlia foliage and flowers. The growers found the grain mix undesirable in appearance so we switched to using A. cucumeris in small sachets. Each paper sachet with a hook contained 1,000 predatory mites and grain mites (all stages), mixed with bran.
Amblyseius cucumeris performs best in temperature under 90F. Maryland temperatures can exceed this in July and August, so in July we switched to sachets of the predacious mite Amblyseius swirskii, which performs better at higher temperatures. This mite is about 2 to 3 times the cost of A. cucumeris.
Materials used: two 100 mL bottles containing 1000 minute pirate bugs.
Pirate bugs were sprinkled at each pepper plant at both sites on August 30, 2018.
Mainspring (cyantraniliprole) at 8 oz./100 gallons of water, applied as a soil drench, was excellent in controlling aphids on treated plants, and provided control for the entire growing season. The Mainspring drench applications did not impact predator releases of the predacious mites or Orius released during our study.
The season of 2018 had records amount of rain in both frequency and abundance. This generally suppressed both Tetranychid mite (two-spotted spider mites) and thrips activity. The dahlias in the biological control/systemic chemical control area had a greater number of blooms and thus had a slightly higher populations of thrips in blooms. The thrips populations remained low on the conventionally-treated plants and the plants that were treated with chemical and biological control.
The banker plants did well, and after the initial release the Orius populations remained active throughout the season. We switched from releasing Amblysieus cucumeris in midsummer to A. swirskii, which costs about three times more.
We encountered a pest during the study that we had not anticipated—spotted cucumber beetle. Working with Jan Meneley of AgBio, Inc of Westminster, Colorado, we evaluated a yellow sticky card baited with pheromone and essence of cucumber extract. The traps worked well in catching insects, and preventing feeding damage to the petal rays of the dahlias.
The quality of the plants and flowers were equally high on the conventional and biological/systemic chemical treated plants.
We would like to conduct a second year of this project, ideally with a less rainy season. We will try reducing the number of biological releases to reduce the cost per plant.
Stanton Gill is an extension specialist (professor rank-principal agent) in IPM and entomology with the University of Maryland Extension based at the Central Maryland Research and Education Center in Ellicott City. He is also a professor in the Landscape Technology Program at the Germantown Campus of Montgomery College. Contact him at [email protected]