Fall armyworm (FAW, Spodoptera frugiperda J.E. Smith) is an invasive lepidopteran pest established in most of sub-Saharan Africa since 2016. Although, the immediate reaction of governments has been to invest in chemical pesticides, control methods based on agronomic management would be more affordable to resource-constrained smallholders and minimize risks for health and the environment. However, little is known about the most effective agronomic practices that could control FAW in typical African smallholder conditions. In addition, the impact of FAW on yield in Africa has been reported as very large, but these estimates are largely based on farmers’ perceptions, but not on rigorous field scouting methods. Thus, the objectives of this study were to understand the factors conditioning FAW infestation in African smallholder maize fields and quantify its impact on yield, using two Districts of Eastern Zimbabwe as cases. 791 smallholder maize plots were scouted for FAW and the head of the corresponding farming household interviewed. Grain yield was later determined in about 20% of these fields. FAW infestation was found to be significantly reduced by weed control – either through herbicides or through frequent weeding operations – and through minimum- and zero-tillage. Conversely, pumpkin intercropping was found to significantly increase FAW infestation. Some maize varieties also appeared more susceptible that others to FAW infestation. Although the infestation levels recorded in this research (35 to 48%, depending on the proxy of infestation used) are commensurate with infestation levels found by other studies conducted on the continent, our best estimate of the impact of this infestation on yield (9.14%) is much lower than what these studies found. Although our study presents limitations, losses due to FAW in Africa could have been over-estimated. The threat that FAW represents for African smallholders, although very real, should not divert attention away from other pressing challenges they face.

1. Understanding factors conditioning fall
armyworm (Spodoptera frugiperda J.E. Smith)
infestation in Chipinge and Makoni Districts and
quantifying its impact on yield
Frédéric Baudron (CIMMYT), Peter Chinwada (UZ), Mainassara Abdou Zaman-Allah (CIMMYT),
Isaac Chaipa (GOAL), & Newton Chari (GOAL)

2. Introduction
• Investing in chemical pesticides has been the immediate reaction of
African governments (Harrison et al., submitted)
• The use of chemical insecticides remains the main strategy of
farmers to control FAW, but with mixed results (Kumela et al., 2018)
• Control methods based on agronomic management are likely more
affordable for resource-constrained smallholders and represent a
lower risk for health and the environment (Thierfelder et al., 2018).
• But lack of data. Data from the Americas and ‘anecdotal’
observations –made in the region (Harrison et al., n.d.).
• Yield impact of FAW reported as very large (ranging from 22 to 67% in
Ghana and Zambia, Day et al., 2017).
• But these estimates are based on farmers’ perceptions, not on
rigorous field scouting methods (such as the one proposed by McGrath
et al., 2018).

3. Objectives
1. To quantify fall armyworm infestation of smallholder
maize in two study Districts following a rigorous
scouting protocol
2. To understand the factors conditioning fall armyworm
infestation
3. To quantify yield losses due to fall armyworm
infestation.

4. Training on FAW (AGRITEX staff in 3
Districts, 15 January 2018)

5. Data collection from 791 plots from
791 smallholder farms
• Chipinge: 2 to 7 February 2018
• Makoni: 22 to 28 March 2018

6. ‘W’ sampling, 5 sampling points of 10 plants
S1
S2
S3
S4
S5
No.
plants
with leaf
damage
No. plants
with frass
in the
whorl
Damage
score for
the 10
plants
S1
S2
S3
S4
S5
(from McGrath et al. 2018)

8. Yield data from 167 plots (~20%)
(Makanza et al. 2018)

9. 48.3 ± 28.4 % 31.8 ± 26.4 % 35.2 ± 26.4 %

10. Chipinge: 41.5 ± 28.7 %
Makoni: 55.1 ± 26.4 %
Chipinge: 26.4 ± 24.8 %
Makoni: 31.2 ± 26.9 %
Chipinge: 34.5 ± 27.7 %
Makoni: 35.9 ± 25.0 %
Estimates of FAW infestation in the
2 Districts

16. Total: 2966.3 ± 1649.9 kg ha-1 Chipinge: 2032.9 ± 1464.1 kg ha-1 Makoni: 3416.3 ± 1547.5 kg ha-1
Estimates of maize grain yield in
the 2 Districts

22. R2 = 0.302
F-value = 67.1
P-value < 0.0001
R2 = 0.002
F-value = 0.30
P-value = 0.5825
Much larger effect of plant population
than FAW infestation on yield

23. Our best estimates of the impact
of FAW infestation on yield losses
Total: 9.1 ± 12.5 %
Chipinge: 13.9 ± 19.3 %
Makoni: 6.9 ± 6.1 %

24. Several factors were found to condition FAW infestation in smallholder
conditions:
• Graminaceous ‘weeds’ are likely to host FAW and increase maize
infestation… but they may also host FAW natural enemies (Hay-Roe
et al. 2016). Trap crop?
• The presence of pumpkin appears to increase FAW infestation.
Cucurbita spp. are known FAW host plants (CABI, 2018). But
pumkins are more likely to provide a day shelter for moths and/or
facilitate maize-to-maize migration of larvae
• Some maize varieties appear more susceptible that others to FAW
(e.g., SC500 series). Potential for selecting for genetic resistance to
FAW (Kumar, 2002).
• Minimum and reduced tillage appear to control FAW, probably
because of higher densities of general predators, as found in Florida
and Mexico (Clark et al., 1993; Rivers et al., 2016)
Conclusions

25. Conclusions
• FAW infestation levels – 26.4 to 41.5% in Chipinge, and 31.2 to
55.1% in Makoni – commensurate with infestation rates found by
other studies (e.g., Day et al. 2017)
• However, our best estimates of the yield impact (9.14% for the total
sample, 12.5% for Makoni, 5.0% for Chipinge) is much lower than
what these studies found (22 to 67%).
• Our approach (rigorous field scouting, harvesting of quadrats) is
probably more accurate than socio-economic surveys.
• Still, limitations of our study (scouting only once in the season, and
probably too early to correlate with significant yield losses)
• Losses due to FAW in Africa could have been over-estimated
– Capacity of maize to compensate, particularly with infestation early in the
development stage. SC500?
• The threat that FAW represents should not divert attention away from
other challenges
– Early dry spell during the season under observation (affecting plant population and
the performance of SC600)

26. Thank you for your attention