This is University of Minnesota Extension service information that is good. Gives you a lot of information about the Japanese Beetle plus control measures for the “Grubs” and “ Adults”.
A multi approach for this insect is best. About 1030 Growing Degree Days is when adults start to show up; they will continue for about 7 weeks
*** If you use a contact pyrethrin; these are light sensitive so spray early in morning or evening after sunset.
The following list of the most common chemicals useful in the control of Japanese Beetles. Always check label before using and observe Re-entry or restricted entry interval (REI) statement. This means the time length of time that must elapse after the pesticide application before individual may enter the treated area without personal protective clothing and equipment.
Pre-harvest interval (PHI) statements indicate time inter-val that must pass after the pesticide application before the crop may be harvested. Harvesting prior to PHI may result in dangerous and illegal pesticide residue on the crop.
Neem extracts and derivatives are products that as anti-molting and digestive disruptors of adult beetles.
Pyrethrum are natural and extracted pyrethrins are botanical insecticides. Concentration varies from 1.4% to 5.0% (these shutdown the insects nervous system)
Temperature, ultraviolet light and rainfall can degrade both of these. Early morning or late evening spraying are recommended. Maybe a residual effect of 4 to 6 days might be expected but additional spraying will have to be done for the duration of the Japanese beetles cycle.
*There might be other sprays that will control Japanese beetles but check the label for approved use on aronia berries before spraying.
New on the scene for JP control is an organic certified BT product that will kill both the larva and adults of a group of beetles which includes JP. Bacillus thuringiensis galleriae is EPA approved and is being produced and distributed by Phyllom BioProducts in California as beetle Gone. Supplies are tight and may not be available for sale at this time.
Figuring Spray amount
Most sprays will use a standard amount of spray mix to apply per acre. As costly as the sprays are, you might be applying too much or not enough if you use the suggested rate on the label.
You are not spraying a total acre. Example: you have 950 plants per acre and have 10 acres.
Measure length of rows X width of plants across. Divide this number by 43,650 sq. ft in an acre. Example: 10 row of 750 feet long and plant width is approx. 5 ft across.
so 750 ft x 10 x 5 ft = 37,500 sq ft
37,500 sq ft divided by 43,560 sq ft = .86 acre. You will only be spraying .86 of an acre
The product calls for 12 oz per acre. You are spraying only .86 of an acre, so you only need 10.32 oz of product.