FLEMINGTON, NJ – Spraying to suppress troublesome black flies is set to resume.

A lobbying effort by officials in Hunterdon and Warren counties has convinced the state Department of Environmental Protection to rejoin the cost sharing partnership with Pennsylvania’s DEP for a non-toxic program to suppress Buffalo gnats – more commonly known as black flies – along the Delaware River, according to a Hunterdon County press release.

“The residents and visitors in Warren and Hunterdon Counties suffer the most if black fly populations are allowed to go unchecked,” Hunterdon Freeholder John King said in the press release. “The renewed program comes as a great relief to the many residents who wish to enjoy their backyards or the county’s parks, trails, and other outdoor recreational activities.”

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According to King, Black flies are not affected by repellents and are extremely painful biters that can cause severe allergic reactions.

“Livestock, pets, farms, wineries, golf courses, outdoor businesses, events, parks, hiking, gardening, in short, any outdoor commercial or private enterprise is subjected to the effects of these pests,” King said, who is credited with spearheading the effort.

New Jersey stopped paying for its share of the program’s cost in the early 2000s.

In 2015, Pennsylvania completely halted black fly treatment on the Delaware because of a lack of funding.

King said the program will be conducted “at no cost to Hunterdon County.”

The spraying by helicopter of a safe, non-toxic pesticide, takes place on both sides of the Delaware River, including Mercer, Hunterdon and Warren counties on the New Jersey side, King said.

New Jersey’s share of the cost of the program is about $200,000. The first new spraying took place on Wednesday.

According to the Pennsylvania DEP, the material used is a naturally occurring bacteria (Bacillus thuringiensis israelensis) that kills the immature (larval) form of the black fly when they feed on it in the waterways. The application is said to be non-toxic to fish or other macroinvertebrates found in the treated waterways.