2019 could be a severe year for sugarbeet root maggot in the Red River Valley

Sugarbeet root maggot flies on sticky stake. Courtesy of Mark Boetel, NDSU Extension.

By Mike Spieker

The sugarbeet root maggot is rearing its head in new areas, said North Dakota State University Research & Extension Entomologist Dr. Mark Boetel in an interview with Mic Kjar at the International Sugarbeet Institute. In 2018, the pest emerged exceptionally early – about 10 days to almost two weeks ahead of the average for its first emergence. High fly activity was seen at the end of May when Boetel and his crew are normally seeing their first fly. 

Boetel said despite a cool April in 2018, a warm May accelerated the maturity of the root maggot. Even with the 2019 spring expected to be a later one, Boetel explained that pressure from high populations last year will carry over into this growing season.

“We are expecting some very high infestation levels this coming year,” said Boetel. Last year the root maggot got away with producing progeny, which are overwintering in the larval state. They will pupate in the spring into the cocoon stage, then emerge as adults. The adults will lay eggs, the eggs will hatch into larvae in late May, usually, and begin doing their damage through August.

The root maggot overwinters around 12-14 inches below the surface and is very tolerant to cold soil temperatures.

Unlike some other sugarbeet weeds and diseases, root maggots are not resistance to any insecticide yet. “That is somewhat alarming because we’ve been using the same main insecticides between 35 and 50 years,” said Boetel. “I’m thinking the development of resistance is probably not an ‘if,’ but a ‘when’. We are on borrowed time I would say.”

Growers can use an at-plant granular material or a seed-applied insecticide to protect their crop against the root maggot. “If they use the seed-applied insecticide, they really have to watch what is going on with our fly counts at NDSU Extension and follow the root maggot model that tracks degree day units to forecast when peaks will occur in fly activity.”

2019 sugarbeet root maggot infestation forecast. Courtesy of Mark Boetel, NDSU Extension.