CSIR research to determine the monetary value of the impact of aphids on selected commercial small grains in the Western Cape concluded that aphid-related problems is insignificant from a financial perspective. Aphids (commonly referred to as plant lice) are small insects that suck sap from plants. The study concluded that the impact of aphids on wheat, oats and barley in the Western Cape is less than 4.4% of the gross income of these industries.

CSIR principal researcher and environmental and resource economist, Dr Willem de Lange, says not much was known about the overall distribution and population structure of cereal aphids in South Africa. This made it difficult to estimate the costs incurred by farmers in terms of pest damage, as well as the costs associated with preventative and treatment-based pesticide application.

The study was part of a bigger study by the Stellenbosch University focusing on the impacts of insecticide overdosing and the cultivation of aphid-resistant small grain cultivars.

As an environmental and resource economist, De Lange applies economic principles to natural resource management. Examples of recent work he has undertaken include an investigation into the viability of tradable permits for green algae pollution, the valuation of pit lake services and investigating incentives for the integration of the mining an agricultural sectors in South Africa.  He recently published a book chapter on water management for greening the South African economy.

De Lange obtained the data used in the study from field visits to several farms; industry data and literature. He found that only 1.9% (R120/ha) of total production cost per hectare goes to pest control.  This figure includes insects, and mammals (mice).  The resultant impact on gross margin is 4.4%, with aphids making up a proportion of the figure.

De Lange says an insect considered to be a secondary pest, namely the Red-legged earth mite (Halotydeus destructor), was cited by all respondent as the most important insect-related problem.  This was unexpected and work is underway to focus on this mite specifically.

“The data suggest that the aphid-related problem in the Western Cape small-grain industry is insignificant from a financial perspective. Farmers confirmed during interviews that aphids are not their most prominent insect-related problem and that insect-related problems are among the smallest of their cultivation-related concerns,” says De Lange.

De Lange warns that the results do not suggest that insects or aphids are an unimportant factor.  “All farmers stressed the fact that aphids needs to be monitored very closely during certain growth stages because whole crop loss will result if left unmitigated.  Consequent mitigation (spraying) is considered highly effective,” he says.