Controlling Adult Japanese Beetles

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Overview

Adult Japanese beetles usually appear in mid-to late June and their feeding can virtually destroy your favorite plants overnight. We know that beetles will feast upon roses (all types), ornamental cherries, crape myrtles, linden trees and birch trees, just to name a few. If you adhere to step #2 in our “Recommendations for Landscape Beds” you’ll be in good shape. Ornamental plants “protected” with imidacloprid will still exhibit a modest amount of feeding damage (“skeletonized leaves”) by Japanese beetles, but remember, the beetle has to take a few bites of leaf tissue to ingest enough of the insecticide.

If you don’t follow Step 2 in our "Recommendations for Landscape Beds”, you can protect your trees with either of the two imidacloprid products sold by THE Turf Plan^®, timing the applications around June 1 to June 7 each year in St. Louis. For those of you in other states, check with your local horticultural extension department, and time your imidacloprid treatments at least 3 weeks prior to the early side of beetle emergence.

Be sure to keep the soil moist for 7 to 10 days after you apply any form of this insecticide, because you want to encourage active root growth, to ensure the that the insecticide will be taken up by roots. Apply Mallet^® 0-0-7 to the root zone of those plants most favored by adult beetles at a rate of 2 TBL/10 sq ft, or 1 cup/100 sq ft, between June 1 and June 7. If you prefer to use the liquid concentrate, Dominion^™ 2L, apply as a foliar spray or a drench. Use our Kalo^® DRI nonionic surfactant when you spray the product. Small (<15 ft tall) shrubs and trees can be protected by a foliar spray or a root drench. To protect large trees, where you can’t spray the entire crown, follow the directions below (directly from the product label).

How To Calculate

Divide the circumference by pi (3.14) to determine diameter. Sticking with the example of Jeff’s pin oak:

1. The drench rate for Dominion^® 2L is 3 to 6 mL per “inch of trunk diameter.”
2. Measure trunk diameter on small trees directly with a tape measure.
1. To calculate the diameter of a large tree, determine the tree trunk circumference by wrapping a tape measure around the tree trunk at 4.5 ft above ground level (diameter at breast height = D.B.H.) (Example exercise below)
2. Divide the circumference by pi (3.14) and that’s the trunk diameter (in inches)
3. Multiply the that number times 6 (mL per inch), to determine the total amount (in mL of concentrate)
4. Divide that product by 30 to convert mL to fluid ounces of concentrate
3. Apply the required amount of imidacloprid in one of four drench techniques, thoroughly explained on the product label: grid system, circle system, basal system or soil drench. Each technique is explained in the product label but the key is to use enough water to ensure even application around the entire 360o around the tree trunk!

Example

A large pin oak in Jeff’s front yard has a circumference of 86 inches

1. 86 inches divided by pi (3.14) = 27.4 inches (diameter of the trunk at 4.5 ft above soil)
2. 27.4 inches times 6 mL/inch = 164 mL
3. 164 mL divided by 30 mL/oz = 5.5 oz

Topics

The Reseeding Bible
Controlling Nutsedge
Moles & Their Control
Irrigation Tips
Our Newest #1 Turf Weed
Controlling Crabgrass
Galls on Pin Oaks
Controlling Adult Japanese Beetles
Grub Control
Know Your Sward Size
Soil Science Basics

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