Orchard Spray Rates
How to Determine the Amount of
Pesticide and Water to Use in Your Orchard

Bulletin 892-01

Calculations for Concentrate Applications,
How much pesticide is needed for a concentrate application?

Method 3: Use the full rate per acre less 20 or 25%.

Once concentrate spraying became a common practice several decades ago, experienced fruit growers and researchers noticed that effective insect and disease control was often obtained when using a lower rate than the full rate per acre. It became a common practice to use 20 or 25% less than the full rate per acre.

For example, for an application to apples of Imidan 70WP, which has a labelled rate of 1 pounds per 100 gallons:

The full rate by the standard conversion =

(1 lb. pesticide/100 gal. water) x (400 gal. water/acre) = 4 lbs. Imidan/acre

To figure 20% less:

(4 pounds per acre) x (0.20) = 0.8 lb.

(4 pounds per acre) - (0.8 pounds) = 3.2 pounds per acre

A quicker way to get the same answer is to take 80% of the full rate:

(4 pounds per acre) x (0.80) = 3.2 pounds per acre

Our older spray guides (1986 and earlier) included a 20% deduction in their published rates per acre. Note: Our current Ohio tree fruit spray guide does NOT use this 20% deduction in the rates per acre.

Advantage of Method 3: It means lower costs per acre for pesticides than if using the full rate per acre.

Disadvantage of Method 3: The 20% rule can work well for some products or some pest targets but not for others; research results are not available to determine exactly when this rule works and when it does not. It might mean that the rate being applied is below the rate stated on the label, thus the label directions are technically not being followed. If a below-label rate is used, the manufacturer cannot be blamed if the product does not perform adequately.

Recommendation: Growers whose experience gives them confidence in using lower rates can certainly use this 20% reduction, but keep liability issues in mind if using lower than the label rate. It is better to use Method 1 or 4 or 5.

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