Once-A-Year Insecticidal Drench w/Merit

Once-A-Year Insecticidal Drench is a systemic imidacloprid insecticide you pour around the base of a tree or shrub. The roots take it up and carry it through the trunk to the leaves, so one spring application protects the whole plant for up to a year without spraying. It is the easiest way to protect a tree too tall to spray.

Not available for sale in Canada or New York State.

What insects does it control?

It controls sap-feeding and wood-boring insects that live inside or on the tree, including aphids, flatheaded borers (including bronze birch borer and emerald ash borer), adult Japanese beetles, lace bugs, leaf beetles, leafhoppers, leafminers, mealybugs, pine tip moth larvae, psyllids, royal palm bugs, sawfly larvae, scale insects, thrips and whiteflies. University of Wisconsin Extension reports that imidacloprid soil drenches give excellent protection against emerald ash borer on ash trees under about 47 inches in circumference (roughly 15 inches across).

How much do I need?

Use 1 oz of concentrate for every inch of trunk circumference, measured at chest height. One 32 oz bottle treats a tree 32 inches around. For shrubs, use 3 oz per foot of height.

How do I apply it?

1. Measure the trunk circumference at chest height and work out how many ounces you need.
2. Mix that amount into 1 gallon of water, or 2 gallons for trees over 50 inches around.
3. Pull back mulch and pour the mix slowly around the base of the trunk, as close to the bark as you can.
4. Rinse the area with clean water. Do not apply to waterlogged or frozen soil; in a dry spell, water the tree the night before.

When should I apply a once-a-year drench?

Apply in spring, before insects become active. For emerald ash borer, extension research recommends mid-April to mid-May, repeated every year. The tree needs several weeks to move the insecticide into the canopy, so a spring drench works far better than one applied after damage appears.

What should I know before using it?

• Do not apply to linden, basswood or any other Tilia species.
• Imidacloprid is toxic to bees. Do not treat plants that are in bloom.
• It is toxic to aquatic invertebrates. Do not apply directly to, or near, lakes, streams, rivers or ponds.
• It does not control spider mites and can make mite outbreaks worse. For mites, use a horticultural oil spray instead.
• Heavily infested trees may still decline. Ash trees that have lost more than half their canopy should be removed rather than treated, and ash trees over about 47 inches around need a professional injection.
• Read and follow the full product label before use.

Drench or trunk injection?

For a tree you can't easily drill, or a shrub, use this drench. If you prefer a measured dose placed directly into the trunk, the Multi-Insect Killer Tree Injection Kit delivers imidacloprid through small holes at the root flare. We stock both at TreeHelp.