Trunk injection and ash treatment: what the university bulletin and state agencies say

This page reports what the named codes, regulators and makers say. It is not training and does not teach the work. This page reports what the official source says. It is not legal advice: ask the office named here. Pesticide licensing differs by state, province and country: the offices are on the pesticide licences guide, and the courses that teach tree work are on the certifications guide. Quarantine rules for ash wood are on the emerald ash borer page, and the wider picture of pests is on the pests and diseases guide.

Four ways of delivering the insecticide

The bulletin Insecticide Options for Protecting Ash Trees from Emerald Ash Borer (third edition, by professors of entomology at Michigan State, Purdue and Colorado State, a former Ohio State professor and a senior scientist at the Morton Arboretum) groups the options into four kinds. It says controlling insects under the bark has always been hard, and that most North American ash have little natural resistance to this beetle.

Delivery	What the bulletin says
Soil-applied systemic	Drenches and soil injections at the base of the trunk take up better than applications in patterns under the canopy away from the trunk. Results were inconsistent: excellent in some trials and poor in others. It says soil applications are not made to excessively sandy soils prone to leaching, nor where roots of flowering plants can be visited by bees. It calls these the only option for many owners who do not hire a professional.
Trunk-injected systemic	Injected directly into the base of the trunk. The bulletin lists as an advantage that they can be used where soil treatment may not be practical or appropriate, such as wet, sandy, compacted or restricted soils. Injection generally means drilling through the bark into the outer sapwood.
Basal trunk spray, noninvasive	Sprayed on the lower trunk with a common garden sprayer at low pressure. The bulletin says it is quick, needs no special equipment, does not wound the tree and puts little into the soil when applied correctly, and that sprayers must be calibrated.
Protective cover spray	Applied to trunk, branches and foliage to kill adult beetles feeding on leaves and newly hatched larvae. The bulletin says control is possible but it is not recommended, because of drift, coverage problems and effects on nontarget species. It says cover sprays have no effect on larvae already feeding under the bark.

Wounds from injection

The bulletin says drilling wounds could cause long-term damage, especially with repeated yearly treatments. It adds that studies of two injection methods found ash trees recovered and made new wood over the wounds in late summer. It also says methods that rely on high-pressure injection through needles can damage the tree if the pressure makes the bark bulge and separate from the cambium, which can kill vascular tissue at that point. It reports that products applied by trunk injection are typically absorbed and moved within the tree faster than soil applications, and that uptake depends on the tree transpiring and on soil moisture, so that drought slows it.

Tree condition

The bulletin says insecticides can stop further damage but cannot reverse injury already done, and that a tree must be healthy enough to carry a systemic product up the trunk. From multi-year studies it says that if more than 50 to 60 percent of the canopy has been killed, or the canopy carries less than half the foliage it should, it is probably too late to save the tree. It says trees already declining when treatment starts may continue to worsen for the first year and usually begin improving in the second. It gives 30 miles as the distance from trees with obvious damage at which it says to consider beginning treatment, and says economic analyses found treating landscape ash with effective systemic products much less costly than removing the trees. No cost figures are repeated here.

What the state agencies say

The Wisconsin Department of Natural Resources says ash in urban and residential settings need insecticidal treatment to be protected, that treatment can prevent infestation of individual trees and treat trees with low to moderate infestation, and that treatments typically need repeated applications for the life of the tree. It suggests consulting a certified arborist about whether trees are worth treating.
Penn State Extension says control tactics are extremely limited, with tree removal the principal option, and that some chemical treatments can be effective when started before large trees are infested.
The University of Maryland Extension page says large specimen trees need to be treated by a certified arborist or licensed tree expert, advises checking that the product label names the beetle, and ties its advice on treatment to protecting pollinators. It also advises hiring an insured, licensed arborist for removal.