Red-headed Flea Beetle
It seems early, but with the unseasonably warm winter, it's time to start thinking about Red-headed Flea Beetle (RHFB).
Growing Degree Days (GDD) for the Piedmont as of 3/11/19
Greensboro- 168.5
Concord- 205.50
Pinehurst NC- 254.00
The following information is from Danny Lauderdale, who has lead the research on this pest.
First generation:
You can begin finding high numbers of hatched larvae as early as 250 GDD for plants overwintered in houses or as late as 500 GDD for those left outdoors and jammed. At most nurseries I have scouted in eastern NC with plants overwintered outside and jammed with winter protection placed on them only during the coldest periods of winter, I usually find larvae active in the substrate at or just after 400 GDD. Adults typically emerge as early as 500 to 800 GDD.
Second generation:
Second generation larvae are active from 1,570 to 1860 GDD50. Second generation adults emerge from 1,878 to 2,318 GDD50.
Pre-larvae hatch control:
If you want a treatment that can be applied before larvae hatch from eggs then here are my one time results: (plants were treated at 200 GDD) (all are drench applications except for the Marathon 1G, which is a granular topdress application)
acephate, Acephate 97UP, 12 oz./100 gal., 94% control
thiomethoxam, Flagship 25 WG, 8 oz./100 gal, 100% control
imidacloprid, Imidacloprid 2F (10.6 oz./100 gal.), Marathon 1G (1 tsp/1 gal topdress and watered in), Marathon II (1.7 oz./100 gal), 100% control
azadirachtin, Azatin O (16 fl. oz./100 gal), 96% control
dinotefuran, Safari 20SC (16 oz./100 gal), 100% control
cyantraniliprole, Mainspring GNL (12 fl. oz./100 gal), 75% control
--note that based on observations from my trials and conversations with other researchers that the neonicotinoid treatments above will protect foliage with these applications as well (I have not taken data on this, just anecdotal observations). Neonicotinoids do not provide great protection as a foliar spray from injury if beetles are already present in large numbers and actively feeding when applied based on the IR-4 research. Drenches are more effective there also based on the IR-4 work.
Post-larvae hatch control:
If you wait until larvae are hatched and present in substrate, I can say that based on two different trials I have done that acephate (I used Acephate 97UP at 12 oz./100 gallons) as a drench resulted in 92% control in the first study and 100% control in the second. Three other products worked well in one study, but I have not had the chance to repeat their use yet. They were chlorpyrifos (Dursban 50W at the highest rate of 16 pounds per 100 gallons--not practical in my opinion and has a 24 hour REI on top of that, did give 100% control and I may repeat at a lower rate and/or with different formulation), Isaria fumosorosea (Ancora--microbial insecticide at 28 oz. per 100 gallons, gave 94% control), and Millenium (Steinernema carpocapsae--beneficial nematodes at 250 million per 100 gallons, gave 100% control). The nematodes have specific application requirements and conditions. Acephate works well and is inexpensive and only a 12 hour REI. Any of the effective treatments would need to be made once larvae have hatched and are found on edges of root balls.
Adult control:
If you let all the eggs hatch and then try to control that huge population of adults feeding, it is a losing battle.
Late season adult control:
Another key is to make sure not to miss late-season foliar applications of adults. If they are left alone, they will lay eggs that will be next year's population. Any species currently being damaged should be a focus of applications next year. The top three species that infect everything else seem to be Itea virginica, Hydrangea paniculata, and Weigela florida.
