Aphid Infestation Score Calculator

The Economic Injury Level (EIL) is the pest density at which the value of crop damage exactly equals the cost of control — the true economic break-even point, as originally defined in Stern, Smith, van den Bosch, and Hagen's 1959 paper "The Integrated Control Concept." The Economic Threshold (ET) is set lower, conventionally at 75% of the EIL, because a grower needs a buffer to scout, decide, and apply treatment before the population actually climbs to the EIL and starts costing more than treatment would.

Treatment efficacy sits in the denominator of the EIL formula, so a less effective treatment (lower kill rate) produces a lower EIL, meaning you'd need to treat at a lower pest density to break even. That's because a weak treatment leaves more of the damaging population alive, so it prevents less loss per dollar spent — the calculator accounts for this by requiring intervention earlier when the treatment itself is less reliable.

No — by definition, once current density exceeds the EIL, the value of yield loss already exceeds the cost of control, so treating pays for itself going forward. What can happen is a large gap between a low ET and a much higher EIL; in that zone treatment is optional rather than urgent, since you're above the action threshold but haven't yet reached the true break-even density.

Crop value (V) is in the denominator of EIL = C / (V × I × D × K), so a higher-value crop reaches economic break-even at a lower pest density — each individual pest is now destroying more dollars of value, so it takes fewer pests to justify the same control cost. This is why high-value specialty crops are typically scouted and treated far more aggressively than low-value commodity crops for the same pest pressure.