Summer in the City of Portsmouth: Weeding and Mosquito Monitoring

August 1, 2023

The Department of Public Works Parks & Greenery Division is trimming, mowing, and conducting garden maintenance as the rains of June give way to abundant plant growth. Prescott Park Garden Tours on Fridays and the seeding in recent construction areas such as Pannaway Park are seasonal reminders of the effort to sustain the urban forest, green spaces and the City’s environment.

Homeowners can assist in these efforts that enhance Portsmouth’s quality of life by pulling weeds in the sidewalks adjacent to their property. In 2017, DPW investigated and began implementing an Integrated Vegetation Management plan that included eliminating the use of synthetic pesticides and implementing organic fertilizing and weed and pest control for a reduced environmental impact. Although funds for this expanded program were cut from the FY19 Budget, staff continue to explore alternative methods of weed control and turf management.

DPW appreciates the efforts of residents to participate in programs such as Adopt-A-Spot, 400 Trees for the 400th, and sidewalk weeding.

Another sign of summer, as the NH Department of Health and Human Services cautions, is the proliferation of mosquitoes, thanks to the greater presence of standing water. NH DHHS notes, “The most important reason to control mosquitoes is to reduce the likelihood of diseases such as Eastern Equine Encephalitis (EEE) and West Nile Virus (WNV) being transmitted to people through mosquito bites. Mosquitoes are most active from June to October.”

In Portsmouth, crews from Dragon Mosquito Control, Inc., the City’s contracted service, are currently checking swamps, salt marshes, woodland pools, ditches, catch basins and other shallow, stagnant water for mosquito larvae. When mosquito larvae are found, treatment may occur using one or more of the following:

  • VectoBac (Bacillus thuringiensis israelensis 2.8%);
  • VectoBac 12 AS (Bacillus thuringiensis israelensis 11.61%);
  • Fourstar Bti CRG (Bacillus thuringiensis israelensis 10%);
  • Natular (spinosad 2.5%);
  • BVA 2 Mosquito Larvicide Oil (mineral oil 97.0%); and
  • SunSpray MLO (mineral oil 98.8%).

Any decision to conduct emergency spraying of adult mosquitoes on City-owned property is made by City officials based on the mosquito surveillance data, disease test results and weather conditions provided by Dragon Mosquito Control. Diseases such as EEE and West Nile Virus are generally found in mosquitoes during the latter part of the summer and early fall. Residents will be advised in advance if spraying is planned.

Residents who do not want their property treated can sign up with the No-Spray Registry at or write to Dragon Mosquito Control, Inc., PO Box 46, Stratham, NH 03885. When writing, residents should be sure to include name, physical address, phone number, the color of the house and acreage or road frontage.

Portsmouth marshland