R4D Special: Scientists discover factors influencing FAW damage in African maize fields in Eastern Zimbabwe

Since the presence of the fall armyworm (FAW, Spodoptera frugiperda J.E. Smith) was reported in Central and Western Africa in early 2016, and later in most of sub-Saharan Africa, it has become a serious threat to food security in the region. Although the immediate reaction of governments was to invest in chemical pesticides and their use remains the main strategy of farmers to control the pest, this has yielded mixed results.

The impact of FAW on maize yield in Africa has been reported as very large with an estimate of  between 22% and 67% yield loss in Ghana and Zambia, resulting in losses running into millions of US dollars, while that of Ethiopia and Kenya were placed at 32% and 47% yield loss, respectively. These estimates are, however, based on socioeconomic surveys focusing on farmers’ perceptions.

Following a rigorous scouting protocol, a team of scientists from the International Maize and Wheat Improvement Center (CIMMYT), GOAL, University of Zimbabwe, and IITA, have reported their findings in a study conducted in the Chipinge and Makoni districts of Manicaland Province in Zimbabwe. They carried out the study to understand the factors influencing FAW damage, quantify yield losses due to FAW damage as well as estimate FAW damage in smallholder maize fields in the two districts.

According to the study, both districts are characterized by high environmental suitability for FAW and dry season cultivation of maize—using irrigation and on riverbanks—which probably allows the pest to persist all through the year.

The study also noted that although governments have invested heavily on chemical pesticides, this is not cost effective and control methods based on agronomic management would be more affordable to resource-constrained smallholders while minimizing risk to health and the environment. However, little is known about the most effective agronomic practices that could control FAW under typical African smallholder conditions.

In addition, the impact of FAW damage on yield was reported as large based on farmers’ perceptions and not on rigorous field scouting methods.

The study grouped soil types into five categories in the 791 fields assessed during the growing season, though only a subset of 167 fields were selected for yield assessment. The researchers used structural equation models to quantify yield losses due to FAW damage while accounting for the fact that variables influencing FAW damage may also influence yield directly.

The study found that several factors influenced FAW damage in smallholder maize fields. However, the results are seen as preliminary, as data analyzed were generated from only two Districts of Zimbabwe and from only one planting season.

The study revealed that frequent weeding operations, through minimum- and zero-tillage significantly reduced FAW damage, while it was observed that pumpkin intercropping significantly increased FAW damage. In addition, damage was noticeably higher for some maize varieties.

Although the levels of FAW damage recorded in this research are commensurate with levels found by other studies conducted in Africa, the best estimate of the impact on yield (11.57%) is much lower than what other studies found. However, the researchers noted that the threat FAW represents for African smallholder farmers, although very real, should not divert attention from other pressing challenges that they encounter regularly.

Frederic Baudron, Mainassara Abdou Zaman-Allah, Isaac Chaipa, Newton Chari, and IITA’s Peter Chinwada, TAAT FAW Compact Leader, carried out the study, which is available in Crop Protection at https://www.sciencedirect.com/science/article/pii/S0261219419300304?via%3Dihub.