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This injector was tested with apple trees.

This injector was tested with apple trees.

Might the airblast sprayer in the future be replaced by IV tubes jabbed in fruit trees?

Michigan State University entomologist Dr. John Wise decided to see if he could control apple insects by injecting insecticides into the tree trunk—much as landscapers now do with some high-value trees to control insects like the emerald ash borer. That invader from Asia has killed 40 million ash trees in the eastern United States in the last decade.

The technology has also been used to control Dutch elm disease on American elms, so both fungicides and insecticides have a history of being injected in trunks.

Wise gave it an initial try on apples in 2009 and followed it up again this year. He showed results during a field day for chemical representatives and fruit growers at the Trevor Nichols Research Complex in Fennville, Michigan, in late September. He is the research and extension coordinator of the station.

Wise stressed that the research is very preliminary. Funding for the tests was minimal. Freezes this spring eliminated fruit from the test block, so most of the results relate to control of foliar-feeding insects, not internal feeders. Tests in 2009 did show that pesticide residues in the fruit were well below federal tolerance levels. Most of the residue was in the leaves, so it’s not clear whether fruit can be protected by this systemic method.

Wise was joined in his testing work this year by Dr. George Sundin, the MSU pathologist who deals with ­diseases like fireblight and apple scab.

The researchers, including two graduate students, drilled small holes low down on the tree trunks and injected into each tree what would be the registered seasonal dose per acre, divided among the 250 trees per acre in the block. They also did a half-rate test. The insecticides they tried were imidacloprid and emamectin benzoate in formulations provided by ArborJet, a company that works with landscapers on emerald ash borer ­control. Treatments were made at petal fall.

Season-long foliage protection was good, Wise said, with control of obliquebanded leafroller and oriental fruit moth being better with ememectin benzoate, and  control of potato leafhopper and spotted tentiform leafminer being better with imidacloprid.

Wise noted that soil-applied systemic insecticides have been used in field crops and potatoes, but that method contributes to issues like groundwater ­contamination and runoff.

Would trunk injection be feasible, given the number of trees that would need to be treated individually? One person commented, “If the science is there, the art will come to it.”

The benefits could be many, Wise said, including reduced worker exposure to pesticides, elimination of spray drift, reduced pesticide impact on natural enemies, and reduced carbon footprint from fewer pesticide ­applications.