Apple maggot infestations seem to be on the increase in Michigan, so growers should have a summertime control program ready this year, reported Michigan State University entomologist Dr. Larry Gut at the December Great Lakes Fruit, Vegetable and Farm Market EXPO.

Numbers do appear to be on the rise, agreed Mike Haas, Michigan State University research assistant at the Trevor Nichols Research Center in southwestern Lower Michigan.

“We have some evidence that they are becoming more prevalent, and that is primarily from adult catches on baited spheres,” he said.

He has not yet completed a comparative analysis to provide a percentage population upturn, but indicated that the numbers have been “increasing moderately” over the past few years.

The upward trend in adult apple maggots probably relates to changes in control measures, Haas said.

“When Guthion dropped out of the list of chemicals you could use for apple maggot, I think that had an impact. A lot of the newer materials aren’t adulticides.”

Specifically, he mentioned that some of the neonicotinoids can kill the larvae and eggs of apple maggots, but aren’t as successful against adults. Likewise, many diamides are listed for apple-maggot suppression only.

He added, “The big picture is we’re losing materials that have been very good against apple maggot, and while the injury in apples has not become a problem, it looks like it’s a possibility that populations are building among adults, and it could potentially become a bigger problem for growers.”

For the coming season, Haas said several materials can do a good job against apple maggots, and Gut suggested the use of such pesticides as Assail (acetamiprid) and Imidan (phosmet) against the insects when they arrive in orchards during the summer.

“The most important thing is to base the start of your apple-maggot program on monitoring,” Haas remarked. He added, “Use either yellow, ammonium-baited sticky cards (early) or red sticky spheres baited with a fruit essence blend (anytime). Check regularly starting at the end of June or when 900 degree-days have accumulated.”

He noted that several applications will probably be necessary.

—by Leslie Mertz