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Improving lives by solving problems in agriculture and the environment

Assessing the impacts of coffee green scale in Papua New Guinea

Almost 90% of Papua New Guinea’s coffee production is supplied by highland smallholder farmers who own less than half a hectare of land and have limited resources. Coffee green scale is a serious pest. Through undertaking regular surveys, this project will build a better understanding of the impact of the pest on the crop yields of smallholders growing Arabica coffee, and its economic consequences. The data will be used to inform decisions about how production can be improved.

Project Overview

So, what's the problem

The majority of Papua New Guinea’s (PNG’s) smallholder farmers grow cash crops on less than ½ a hectare of land or with limited resources. These farmers account for nearly 90% of the country’s coffee production, earning 5% of GDP in foreign exchange income – the second largest in the agricultural sector.

Currently coffee green scale, a combination of two scale insect species, is described as the most serious pests. Although much is known about the pests from studies in both PNG and other countries, little is known about yield loss for the highland smallholders. An estimated loss of 50% of the yield on affected farms is often quoted for Arabica coffee, but data is lacking. Therefore, there is a need to understand the impact of this problem on the crop yields of smallholders and its economic consequences.

What is this project doing?

The project will address the impact of coffee green scales on yield loss and the economic impact of highland smallholders growing Arabica coffee. The main focus will be on smallholders but the team will also execute on station trials and include larger growers/plantations where they are more likely to keep historical information on coffee green scales, yield, and yield loss.

The projects aims to quantify the impact of coffee green scale, in terms of yield loss, in highland smallholder coffee farms in Papua New Guinea. We will also estimate the potential economic impacts to smallholder farmers. To do this, the team will undertake regular surveys of coffee green scale infestations on a selection of smallholder farms within the Eastern Highlands and assess the impact on yields. A maximum of six surveys per year will be conducted from the onset of flowering through to harvest for two growing seasons at around 1500m (where the incidence of coffee green scales is known to be greatest). This way, we will be able to estimate the overall loss due to coffee green scales on total highland smallholder production.

The project will develop relations with smallholders, owners of larger farms, and processors, and establish field experiments at the research station. Ecological and socio-economic surveys will be implemented on smallholder farms in the Eastern Highlands. The impact that coffee green scales have on yields will be estimated by comparing smallholder farms both with and without the pests. We will estimate overall yield loss by comparing smallholder farms with well managed coffee systems (e.g. some large farms) and data from field experiments. The incidence of coffee green scales and its economic impact will be assessed in other major coffee growing provinces (i.e. the Western Highlands and Simbu Provinces). Estimates of overall yield loss will be compared with the perceptions of smallholder farmers in order to inform the development of management plans.

The findings will facilitate efforts to improve decisions about sustainable coffee production for smallholders; it will assist in improving productivity through identifying actual yield loss due to coffee green scales infestations. Steps to mitigate yield loss due to coffee green scales can then be better integrated into current and future education and management programs. Additionally, it will contribute to the ACIAR in-country research programme and will also support the AusAID strategy for the country by quantifying the actual and economic impact of coffee green scales on yields and livelihoods.


So far, the project team has conducted most trips to the country and compiled reports of our findings to our project partners and sponsor – ACIAR.

Alex Brook visited Papua New Guinea to survey green scale on smallholder cofffee gardens. We have created a short photodiary video of his visit, including a short explanation from a local farmer regarding the symptoms resulting from coffee green scale infestation.

We also have a video of the impacts of coffee green scale.

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