Homeowners in St. Charles County should treat eastern red cedar for bagworms in late May through early June when larvae are small and most vulnerable. Waiting past mid-June allows the bags to harden and reduces control success on properties we monitor across the area.
Spotting Early Infestations
Eastern red cedar and nearby flowering dogwood suffer heavy defoliation when bagworm numbers exceed five bags per branch. Walk the canopy edge in April and count the overwintering bags before new growth starts. Heavy clay soils in St. Charles County slow tree recovery, so early detection prevents stress that compounds during hot-humid summers.
Treatment Timing That Matches Local Weather
Apply Bacillus thuringiensis or a labeled insecticide between May 25 and June 10 in zone 6. These dates align with the end of freeze-thaw cycles and before summer windstorms arrive. One thorough spray at 2 gallons per tree covers most 15- to 25-foot specimens common in Wentzville and Cottleville yards. A second application 10 days later catches any late hatch if temperatures stay above 70 degrees.
Follow-Up Care Through Summer
Remove and destroy fallen bags in July to cut next year's population. Water newly treated trees with 20 gallons once a week during July and August to offset clay soil compaction. Eastern red cedar holds its shape better when bagworm pressure stays below two bags per branch heading into winter.
For professional bagworm scouting and treatment on your property, Contact Us.