The feasibility of combating harmful organisms in agricultural activities is determined in different ways. Some advocate for preventive treatments, while others support treatments based on the harmful organism reaching specific criteria. Preventive spraying, usually timed to the phenophases of the crop, is simpler to implement (and does not require highly qualified agricultural services). However, this approach tends to be more costly overall and places a heavier strain on both the environment and public health, as treatments are often applied across entire areas without selectivity. In the early stages of investment, some newly established large agricultural enterprises may opt for preventive applications. During years when grain market competition intensifies - so-called “harvest years” - farms with a significant share of their budget allocated to crop protection measures are compelled to evaluate the economic justification for such interventions. In these cases, decision-making must rely on cost-benefit criteria, particularly the use of economic thresholds of pest damage as a basis for feasibility assessments.

There are two concepts: the threshold of harmfulness (TH) and the economic threshold of harmfulness (ETH). The TH refers to the population density of a harmful organism or the damage to plants at which noticeable harm to the crop occurs, while the ETH refers to the population density of a harmful organism or the damage to plants at which the costs of protective measures are compensated or comparable to the damage incurred.

In most countries, the justification for protective treatments is commonly based on achieving a return that is two to three times greater than the initial investment in those measures.

The economic threshold of harmfulness (ETH) serves as a critical reference point for determining when chemical control methods are warranted. Despite its apparent simplicity, the ETH is influenced by a complex web of interrelated factors. These include the cost, efficacy, and application rate of pesticides; the number and timing of treatments; pest population density and age composition; their spatial distribution within fields; and the physiological condition of the pest species. Additional considerations include the activity and efficiency of natural enemies (entomophages), prevailing weather patterns, crop variety, agronomic practices, and the current health and developmental stage of the crop. Furthermore, the intended purpose of the harvest - such as market value and potential income gains relative to additional expenditures for crop protection - also plays a significant role. All of these variables must be integrated when assessing whether pest control interventions are economically justified.

One of the more straightforward formulas used to determine the economic threshold of harmfulness (ETH) for high-value crops is presented below (Vozov, Polyakov, 1968):

ETH = C×N×P/Y, 

where C - costs for plant protection, tenge/ha; N is the number of destroyed pests per hectare; P is profitability, %; and Y is preserved yield, tenge/ha.

For accurate ETH calculations, it is important to estimate the expected crop yield as precisely as possible, as this parameter tends to contribute the greatest margin of error. In practice, yield projections are most effectively developed in consultation with the farm’s agronomist, whose expertise helps refine these estimates.

More advanced models, which incorporate a broader range of variables - including ecological and social impact criteria - are available in specialised scientific literature (Chiang, 1982; Zakharenko, 1986; Tansky, 1988, etc.). 

If calculating ETH is complicated, published data can be used (Table 1).

Table 1 - Economic threshold of harmfulness for major pests of spring wheat