Ash trees are currently in the “problem” stage with a new pest that’s sweeping across North America – the Emerald Ash Borer.
Small trees (diameter under one inch) were planted in an area where the mature trees destroyed by the borer had been disposed of. So a good supply of borers
Azidarachtin – a derivative of Neem tree seeds – was injected into the trees in varying concentrations. With the higher application rates, all larvae were killed. But no adults were hurt. (rather a good news – bad news kind of thing)
Now – researchers are working on larger trees and trying to establish the level of chemical necessary to stop the larval stage. It would appear there’s a solution on the horizon but it’s likely going to take a few years.
Note that simply spraying the trees doesn’t do anything because the adults don’t seem bothered by the chemical and the larvae are protected within the tree – the chemical had to be injected to be effective.
This means when you hear through the grapevine that neem will kill off emerald ash borers – you know the truth.
Reference: Nicole McKenzie (Dept. of Environmental Biology, University of Guelph, Guelph, Ontario, CANADA N1G 2W1), Blair Iielson, Dean Thompson, Gard Otis, John McFarlane, Tere- sa Buscarini, and Joe Meating, “Azadirachtin: An Effective Sys- temic Insecticide for Control of Agrilus planipennis (Coleoptera: Buprestidae,” Journal of Economic Entomology 103(3), June 2010, 708-717. (Entomological Society of America, 10001 Derekwood Ln., Lanham, MD 20706-4876.)