Ferti-lome Tree & Shrub Systemic Insect Drench is a soil-applied insecticide that you mix with water and pour around the base of your trees or shrubs. The basic formula is simple: 1 fluid ounce of product per inch of trunk circumference, mixed into 1 gallon of water. Here’s everything you need to know to apply it correctly.
How the Product Works
This is a systemic insecticide, meaning it doesn’t sit on the surface of leaves waiting for bugs to land on it. Instead, the solution soaks into the soil, gets absorbed by the roots, and travels upward through the plant’s vascular system into the trunk, branches, and leaves. It even moves into new growth that appears after you apply it. Because the insecticide is inside the plant tissue, rain and irrigation can’t wash it off.
The active ingredient is imidacloprid at a 1.47% concentration. It targets common sap-feeding and leaf-chewing insects like aphids, whiteflies, scale, Japanese beetles, leafminers, and borers. One application provides up to 12 months of protection. The trade-off for that long-lasting coverage is patience: depending on the size and health of your plant, full distribution from roots to canopy can take anywhere from one week to three months. Large trees take the longest.
How to Measure Your Tree
Your dosage depends on trunk circumference, not diameter. Wrap a flexible tape measure around the trunk at chest height (about 4.5 feet above the ground) and note the measurement in inches. That number tells you exactly how many fluid ounces of product to use. A tree with a 20-inch circumference gets 20 fluid ounces. A tree with a 35-inch circumference gets 35 fluid ounces.
If you don’t have a tape measure handy, you can estimate circumference from diameter by multiplying the trunk diameter by 3.14. A trunk that’s roughly 6 inches across has a circumference of about 19 inches.
Mixing and Dosage for Trees
The ratio is 1 oz. of product per inch of trunk circumference, dissolved in 1 gallon of water. For most trees, that single gallon is your total application volume. Here are some common examples from the label:
- 8-inch circumference: 8 fl. oz. in 1 gallon of water
- 15-inch circumference: 15 fl. oz. in 1 gallon of water
- 25-inch circumference: 25 fl. oz. in 1 gallon of water
- 40-inch circumference: 40 fl. oz. in 1 gallon of water
- 50-inch circumference: 50 fl. oz. in 2 gallons of water
Notice that once you reach the 50-inch range and above, the label calls for 2 gallons of water instead of 1. This simply ensures the solution spreads evenly across the larger root zone of a big tree.
Where to Pour the Solution
Don’t dump the mixture right at the base of the trunk. Instead, pour it in a circular band that starts at the trunk and extends outward about 2 feet in all directions. You’re targeting the root zone where feeder roots will absorb the product most efficiently.
For larger trees with trunk diameters over 16 inches (roughly 50 inches in circumference), widen that band to 3 to 4 feet out from the base and use 2 gallons of solution. The goal is even coverage across the soil where the roots are actively growing. Pour slowly and evenly so the liquid soaks in rather than running off to one side.
Dosage for Shrubs
Shrubs don’t have a single measurable trunk the way trees do, so the approach is a bit different. For multi-stemmed shrubs, you can measure the circumference of the largest stem or estimate based on overall plant size. The same 1 oz. per inch ratio applies if the shrub has a defined woody trunk you can measure. For smaller ornamental shrubs, the label typically calls for a reduced amount of product mixed into a smaller volume of water, poured evenly around the root zone at the base of the plant. Apply the solution in the same circular band pattern you’d use for a tree, scaled down to match the shrub’s root spread.
Best Time to Apply
Because the product can take weeks or even months to fully distribute through a large plant, timing matters. Apply well before you expect pest pressure to peak. For most situations, early spring is ideal. The plant’s roots are actively growing and pulling water from the soil, which means they’ll absorb the insecticide efficiently. Applying during active growth, when the plant is not dormant or drought-stressed, gives the best uptake.
Make sure the soil is moist but not waterlogged before you apply. If the ground is bone dry, water the area lightly a day before application. This helps the solution soak down to the root zone rather than sitting on top of dry, compacted soil. After applying, you can water lightly again to help move the product deeper, but avoid heavy irrigation that might push it past the root zone entirely.
Pollinator Safety
Imidacloprid is a neonicotinoid, a class of insecticides that is highly toxic to bees and other pollinators. This is the single most important caution with this product. If your tree or shrub produces flowers that bees visit, the insecticide will be present in the pollen and nectar once it moves through the plant’s system.
Avoid applying to plants that are currently blooming or will bloom within the coming weeks. For flowering trees like crabapples, cherries, or lindens, the safest approach is to apply immediately after bloom is finished, giving the product time to distribute while minimizing exposure during peak pollinator activity the following season. If the plant is purely ornamental and never flowers, or if its flowers don’t attract bees, this is less of a concern. Keep the product away from water sources as well, since imidacloprid is toxic to aquatic invertebrates.
Tips for an Effective Application
Pull back any mulch from around the base of the tree before pouring. Thick mulch can absorb the solution and prevent it from reaching the soil surface where roots can take it up. Once the liquid has soaked in, you can replace the mulch.
Don’t apply more than once per year. The product is designed to provide 12 months of systemic protection from a single application, and over-applying won’t speed up the process. If you’re treating a very large tree and don’t see results within a few weeks, that’s normal. Give it the full one to three months before assuming the treatment didn’t work.
Store any unused product in its original container, out of direct sunlight and away from extreme heat or cold. The 32-ounce bottle covers a single tree with a trunk circumference of about 32 inches, so for properties with multiple trees, plan your purchases accordingly.