Fall armyworms can be devastating for corn and also feed on a variety of grasses. Some researchers have suggested that if northern locations begin to experience warmer winters, fall armyworm could become a more frequent pest in the northern U.S. This resource covers organic management practices for fall armyworm.
Midwest
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2023
Fact Sheet Series 23-1
Organic Grain Resource and Information Network | The University of Wisconsin-Madison | www.ograin.cals.wisc.edu
Organic Management of Fall Armyworm Spodoptera frugiperda (JE Smith)
Summary
•
In 2021 the upper Midwest experienced an unusual fall armyworm infestation.
•
Fall armyworms can be devastating for corn and also feed on a variety of grasses.
•
The only organic management option in northern regions is well-timed foliar sprays of Bt or Spinosad. These
treatments are most effective in early larval stages, so timing is critical.
•
Pest monitoring programs can assist with management decisions, including updates from the University of
Wisconsin-Madison at https://ipcm.wisc.edu/wcm/ and University of Missouri’s fall armyworm monitoring
network (https://ipm.missouri.edu/pestMonitoring/faw/index.cfm).
INTRODUCTION
In 2021, the upper Midwest saw an unprecedented
fall armyworm infestation. Fall armyworm is a highly
invasive and destructive pest that can be devastating to
corn. It is not usually a concern this far north; however,
in 2021 some growers in Wisconsin experienced
economic issues, while growers in regions to the south,
including Indiana, experienced even greater losses (1,2).
one. A distinguishing feature of older armyworm larvae
is an inverted “Y” on their head.
Fall Armyworm Identification
Many factors affect the level of damage induced by
pest populations each year including insect migration
patterns and weather conditions (3). It is possible that
the 2021 infestation was a rare occurrence and will
not impact future years. However, some researchers
have suggested that if northern locations begin to
experience warmer winters, fall armyworm could
become a more frequent pest (1,4).
Pest monitoring networks can often provide early
alerts about fall armyworm populations to help assist
with management decisions. This fact sheet will cover
organic management of fall armyworm with a focus on
organic corn production.
APPEARANCE
The fall armyworm moth has forewings that are
mottled with dark gray and light gray while the
hindwings are silver-white (3,5). In males, each
forewing has a white patch at the tip. Fall armyworm
eggs are dome shaped and about 0.4mm in diameter
(6). They are laid in masses, commonly of 100-200 eggs,
usually in a single layer attached to foliage; however,
they can be deposited in layers.
Newly hatched larvae are only a few millimeters long
and greenish in color with a black head that changes
to orange over time (6). Full grown larvae are around 1
to 1.5 inches long and can be light tan or green to black
with 3 thin yellow stripes running down their length. On
either side of their body is a thicker brown stripe next
to a yellow stripe about the same width as the brown
Organic Management of Fall Armyworm
Top: Fall armyworm larvae (damaging stage). Bottom:
adult female (F) and male (M). Image credit: Integrated
Pest Management, University of Missouri. Available
at: https://ipm.missouri.edu/pestmonitoring/faw/
identification.cfm
LIFE CYCLE
Fall armyworm cannot survive cold temperatures.
Therefore, they only overwinter in the southernmost
states, including Texas and Florida (1). In the spring
and summer, fall armyworm moths begin to migrate
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northward. After a few generations, fall armyworm can
reach as far north as the upper Midwest and Canada,
which typically happens mid to late summer. Usually,
they reach the upper Midwest too late in the season for
concern, but this is not always the case.
Female armyworm moths usually deposit eggs when
they are 4 to 5 days old but can do so for up to 3 weeks
(6). Eggs are usually laid in masses of 100 to 200 in a
single layer attached to foliage, with a preference for
whorl-stage corn (7), and each female lays an average
of 1500 eggs over her lifetime.
The speed of development and the number of
generations that occur in a specific area both depend
on the temperature. During hot summers, the eggs
hatch in 2 to 3 days but can take up to 10 days (6,7).
Newly hatched larvae are too small to do much
damage, but older larvae are highly destructive. In hot
weather, larval development takes around 14 days
while in cooler fall temperatures it can last 30 days.
The pupal stage can extend from 8 days in hot weather
to 30 days in cooler weather. Adults live for about 10
days on average but can survive up to 21 days. Overall,
the length of their life cycle ranges from 30 days in hot
summers to 60 days in the spring and fall, and even
longer where they overwinter.
pheromone traps for moths, or when damaged plants
are first seen (3,6,7). If either is found, then look for eggs
and larvae. Larvae can be found on leaves, sometimes
deep within the whorl, on tassels, and ears. Fall
armyworms are cannibalistic, so usually only 1-2 older
larvae occupy a single plant. If there is fall armyworm
damage on plants but no larvae are present, it is
possible that they have pupated, and the infestation
may be over. Sampling 20 plants in 5 areas or 10 plants
in 10 areas is suggested to determine the proportion of
plants affected.
Pest monitoring programs can assist with management
decisions by providing early information about fall
armyworm populations. Updates from the University
of Wisconsin-Madison can be found at Wisconsin Crop
Manager news (8) at https://ipcm.wisc.edu/wcm/ (you
can also sign up for their newsletter on the website).
There are also monitoring networks specific to fall
armyworm in more southern states, including the
University of Missouri’s fall armyworm monitoring
network (9) available here: https://ipm.missouri.edu/
pestMonitoring/faw/index.cfm.
Leaf Damage on Corn due to Fall Armyworm
Considerations for Wisconsin
• If fall armyworms arrive late in the season, they
may only last one generation before it is too cold
for their survival
• Late season cooler temperatures could prevent fall
armyworm eggs from hatching or slow down their
development, which could make them vulnerable
to control measures for a longer period of time
before they reach their most destructive stages (1)
Photo credit: Paul Choate, University of Florida (6).
Available at: https://entnemdept.ufl.edu/creatures/
field/fall_armyworm.htm
SYMPTOMS AND EFFECTS
ORGANIC MANAGEMENT
Fall armyworm has a range of host plants but prefers
grasses including field corn and sweet corn and also
feeds on alfalfa, buckwheat, barley, oats, clover, millet,
ryegrass, Sudangrass, soybean and wheat (6).
If fall armyworm populations are above threshold levels
(greater than 15% of plants infested with larvae), control
measures are recommended (7). The only management
option for organic production systems in northern
regions is well-timed biological foliar sprays. Bacillus
thuringiensis (Bt) products are commonly used and
spinosad is another option. If targeting fall armyworm,
these products can be used at any time of year and at
any crop stage. Treatment is most effective when fall
armyworms are in early larval stages, so timing of the
application is critcal. Optimal timing can be achieved
through scouting and monitoring.
Larvae consume foliage and while newly hatched
larvae don’t cause much destruction, older larvae cause
extensive damage. On corn plants they can feed deep
in the whorl, leading to a pattern of perforations in the
leaves. They also feed in tassels and ears, including
eating through the side of the ear (7). Older larvae
leave behind ragged looking corn plants, which may
resemble hail damage, or sometimes only ribs and
stalks remain. They also can limit further plant growth
by burrowing into the growing bud.
SCOUTING AND MONITORING
It is recommended to start scouting for fall armyworm
when corn is at whorl stage either using blacklight or
Organic Management of Fall Armyworm
Bacillus thuringiensis (Bt)
Bt is a bacterium that occurs naturally in soil. Bt spores
produce compounds that are toxic to insect larvae
if the larvae ingest them (10,11). They are not harmful
to humans and other mammals, are practically nontoxic in birds and fish and have little-to-no toxicity to
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non-target insects including many beneficial insects.
The strains Bt aizawai or Bt kurstaki act against moth
and butterfly caterpillars and are recommended for
fall armyworm. They are most effective against young
larvae. These sprays have a short residual time in the
field, with half-lives of 1-4 days on foliage. For effective
fall armyworm management, it is recommended to
have the product on foliage as the larvae are emerging.
For further information on applying Bt products, refer
to product labels or consult your agricultural extension
agent.
It is important to note that instances of fall armyworms
showing field resistance to Bt corn have been
documented, including in the US (12,13). The same type
of toxin that results from using a Bt spray can also be
present in a Bt corn hybrid, depending on the hybrid
and the specific product used. This raises the concerns
that fall armyworm could begin to develop resistance
to Bt sprays over time.
Spinosad
Spinosad is made by a soil bacterium and can be toxic
to insects that come into contact with it or ingest it (14).
It has low toxicity in people and other mammals and
is practically non-toxic to moderately toxic to fish and
birds. It is moderately toxic to earthworms and highly
toxic to bees, but studies suggest that after the spray
has dried it is no longer toxic to honeybees or other
beneficial insects. It lasts a bit longer in the field than
Bt products, with a half-life on foliage of 2-16 days.
For further information on applying spinosad, refer to
product labels or consult your agricultural extension
agent.
REFERENCES
Resources in bold are especially recommended for
further reading.
1. Fall Armyworms: A Late Summer Surprise in Wisconsin. University of
Wisconsin Insect Diagnostic Lab. 2021. Accessed 2022 Oct 25. Available
from: https://insectlab.russell.wisc.edu/2021/09/29/fall-armywormsin-wisconsin/
2. Jensen B. Fall Armyworm: Keep looking. University of Wisconsin
– Madison Integrated Pest and Crop Management. 14371. Accessed
2022 Nov 1. Available from: https://ipcm.wisc.edu/blog/2021/10/fallarmyworm-keep-looking/
3. Fall Armyworm. Purdue University Field Crops IPM. Accessed
2022 Oct 25. Available from: https://extension.entm.purdue.edu/
fieldcropsipm/insects/fall-armyworm.php
4. Thomas M. Fall armyworms are causing damage in fields
throughout the Midwest. WLFI News 18. Accessed 2022 Nov 1.
Available from: https://www.wlfi.com/archive/fall-armywormsare-causing-damage-in-fields-throughout-the-midwest/article_
ebfe1fd8-d8b2-5f92-acb4-3a15d6c77c8e.html
5. Fall Armyworm Identification & Scouting. Integrated Pest
Management, University of Missouri. Accessed 2023 May 16. Available
from: https://ipm.missouri.edu/pestmonitoring/faw/identification.cfm
6. Capinera JL. Featured Creature: Fall Armyworm. University of
Florida Institute of Food and Agriculture. Accessed 2022 Oct 31.
Available from: https://entnemdept.ufl.edu/creatures/field/fall_
armyworm.htm
7. Hazzard R, Westgate P. Organic Insect Management in Sweet
Corn. Sustainable Agriculture Research & Education; 2005. Accessed
2022 Nov 1. Report No.: 01AGI2005. Available from: https://www.
sare.org/resources/organic-insect-management-in-sweet-corn/
8. WCM news. Integrated Pest and Crop Management; University of
Wisconsin-Madison. 2023. Accessed 2023 May 17. Available from:
https://ipcm.wisc.edu/wcm/
9. Missouri Pest Monitoring Network – Fall Armyworm. Integrated
Pest Management, University of Missouri. Accessed 2023 May 16.
Available from: https://ipm.missouri.edu/pestMonitoring/faw/
index.cfm
10. Bacillus thuringiensis Fact Sheet. National Pesticide Information
Center, Oregon State University; 2022. Accessed 2022 Nov 3. Available
from: http://npic.orst.edu/factsheets/btgen.html
Authors
Emily Bick1, Claire Stedden2, Erin Silva3
1. Assistant Professor, Department of Entomology,
University of Wisconsin-Madison; 2. Outreach
Specialist, Department of Plant Pathology, University of
Wisconsin-Madison; 3. Associate Professor, Department
of Plant Pathology, University of Wisconsin-Madison.
Released: May 2023
Digital version available at: www.ograin.cals.wisc.edu
11. Dewerff R, Jensen B, Liesch PJ, Nice G, Renz M, Smith D, et al. Pest
Management in Wisconsin Field Crops. Extension, University of
Wisconsin-Madison; 2020. Report No.: A3646.
12. King C. Insect resistance to BT corn. Top Crop Manager. 2020.
Accessed 2023 May 16. Available from: https://www.topcropmanager.
com/insect-resistance-to-bt-corn/
13. Huang F. Resistance of the fall armyworm, Spodoptera frugiperda,
to transgenic Bacillus thuringiensis Cry1F corn in the Americas:
lessons and implications for Bt corn IRM in China. Insect Science.
2021;28(3):574–89.
14. Spinosad General Fact Sheet. National Pesticide Information
Center, Oregon State University; 2014. Accessed 2022 Nov 4. Available
from: http://npic.orst.edu/factsheets/spinosadgen.html
The OGRAIN (Organic Grain Resource and Information Network) program is housed in the Organic and Sustainable Agriculture
Research and Extension Program within the University of Wisconsin-Madison Department of Plant Pathology under the
leadership of associate professor Dr. Erin Silva. OGRAIN provides resources and support for new, transitioning, and experienced
organic grain farmers throughout the upper Midwest. We host a variety of events, support a producer listserv (join by emailing
join-ograin@lists.wisc.edu) and provide educational materials at https://ograin.cals.wisc.edu/. To contact us, email Erin at
emsilva@wisc.edu, or call (608) 890-1503.
Organic Management of Fall Armyworm
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