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Plantwise Technical Factsheet

beet armyworm (Spodoptera exigua)

Host plants / species affected
Abelmoschus esculentus (okra)
Allium
Allium cepa (onion)
Allium cepa var. aggregatum (shallot)
Allium fistulosum (Welsh onion)
Allium sativum (garlic)
Amaranthus (amaranth)
Amaranthus hypochondriacus
Apium graveolens (celery)
Apium graveolens var. rapaceum (celeriac)
Arachis hypogaea (groundnut)
Asparagus officinalis (asparagus)
Atriplex (orach)
Beta vulgaris (beetroot)
Beta vulgaris var. saccharifera (sugarbeet)
Brassica
Brassica oleracea var. botrytis (cauliflower)
Brassica oleracea var. capitata (cabbage)
Brassica oleracea var. gemmifera (Brussels sprouts)
Brassica oleracea var. italica (broccoli)
Brassica oleracea var. viridis (collards)
Brassica rapa subsp. pekinensis
Capsicum (peppers)
Capsicum annuum (bell pepper)
Carthamus tinctorius (safflower)
Chrysanthemum (daisy)
Chrysanthemum indicum (chrysanthemum)
Cicer arietinum (chickpea)
Citrullus lanatus (watermelon)
Citrus
Corchorus (jutes)
Corchorus capsularis (white jute)
Coriandrum sativum (coriander)
Cucumis melo (melon)
Daucus carota (carrot)
Dianthus caryophyllus (carnation)
Eryngium foetidum
Fragaria ananassa (strawberry)
Glycine max (soyabean)
Gossypium (cotton)
Guizotia abyssinica (niger)
Gypsophila (baby's breath)
Gypsophila paniculata (baby’s breath)
Helianthus annuus (sunflower)
Impatiens (balsam)
Lactuca sativa (lettuce)
Linum usitatissimum (flax)
Malva (mallow)
Medicago sativa (lucerne)
Musa (banana)
Musa x paradisiaca (plantain)
Nicotiana tabacum (tobacco)
Oryza sativa (rice)
Pelargonium (pelargoniums)
Pennisetum glaucum (pearl millet)
Phaseolus vulgaris (common bean)
Pisum sativum (pea)
Poaceae (grasses)
Populus deltoides (poplar)
Rosa (roses)
Sesamum indicum (sesame)
Solanum lycopersicum (tomato)
Solanum melongena (aubergine)
Solanum tuberosum (potato)
Spinacia oleracea (spinach)
Trifolium (clovers)
Triticum aestivum (wheat)
Vicia faba (faba bean)
Vigna unguiculata (cowpea)
Zea mays (maize)
List of symptoms/signs
Fruit  -  external feeding
Growing point  -  external feeding
Inflorescence  -  external feeding
Leaves  -  external feeding
Symptoms
Young larvae feed on the under surface of leaves where they eat the lamina but often leave the upper epidermis and larger veins intact. Larger larvae make irregular holes in leaves and fully-grown larvae devour foliage completely, leaving only major veins. On tomato plants, buds and growing points may be eaten and fruits pierced.
Prevention and control

Cultural Control

Control is largely achieved in the northern range through a winter kill by exposing larvae and pupae within the upper soil surface. Freezing temperatures cause high larval mortality. Therefore, clean cultivation and weeding are recommended.

Biological Control

The importance of natural enemies has been demonstrated in cotton in the southeastern USA in which a large and diverse complex of predatory arthropods, parasitoids and pathogens appear capable of maintaining populations below economically-damaging levels. Disruption of this complex with the use of insecticides contributes to outbreaks of S. exigua. It can also exacerbate problems with other pests because the complex of beneficial organisms attacking the noctuid is comprised of generalist species that also suppress other pests in the cotton production system (Ruberson et al., 1994).

The compound N-(17-hydroxylinolenoyl)-L-glutamine called volicitin was isolated from oral secretions of S. exigua larvae. When applied to damaged leaves of maize seedlings, volicitin induced the seedlings to emit volatile compounds that attracted females of the parasitoid Cotesia marginiventris. Mechanical damage of the leaves, without application of this compound, did not trigger release of the same blend of volatiles. Volicitin appears to regulate tritrophic interactions among plants, insect herbivores, and natural enemies of S. exigua (Alborn et al., 1997).

Host-Plant Resistance

Breeding programs for resistance to Spodoptera spp. have developed field crop varieties with improved resistance, one example being maize (Mihm et al., 1988). The resistance mechanism that appears to be operating in maize is increased leaf toughness, vis-à-vis a thicker epidermis (Davis et al., 1995). In celery, the mechanism of resistance involves linear furanocoumarins such as psoralen, xanthotoxin and bergapten, which appear in higher concentration in resistant varieties (Brewer et al., 1995).

Transgenic maize containing genes encoding delta-endotoxins from Bacillus thuringiensis kurstaki have been commercialized in the USA. S. exigua is controlled by these toxins but it appears that resistance breakdown may occur quickly (Moar et al., 1995). Vegetative insecticidal proteins (vip) have been isolated from Bacillus thuringiensis (Bt) during the vegetative phase of growth which show a wide spectrum of activities against lepidopteran insects, especially Spodoptera spp.(Estruch et al., 1996).

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:


Impact
S. exigua is a pest of cotton, soyabeans, sugarbeet, lucerne and maize in the USA, Iraq, Syria, Ethiopia, Egypt, Sudan and Central Asia and Central America (Kranz et al., 1977). King and Saunders (1984) suggested an economic threshold of two larvae per five plants.

In the USA, there were widespread outbreaks of S. exigua on cotton in Texas in 1995. The amount of damage caused varied widely from area to area and over 3 million acres were infested to varying degrees. About 1.2 million acres were treated at a cost of >US$ 31 million (Huthman, 1996). Hardee and Herzog (1996) reported that S. exigua reduced cotton yields by 1.68% in 1995 in the USA.

Cotton-growing areas in Georgia in 1988 were also infested by S. exigua. The area requiring control was 89,505 ha while 102,060 ha was actually treated with insecticides. Production losses on treated areas were 2820 t (Lambert et al., 1989 in Oerke et al., 1994).

Soyabean-growing areas in Georgia, USA, were also infested by S. exigua in 1988. The area of soyabeans requiring control was 11,340 ha while 15,000 ha was actually treated. The cost of control was $558,000. The crop loss on treated areas was 272 t (Adams et al., 1989 in Oerke et al., 1994).

The use of insecticides and the subsequent effect on yield was assessed on soyabeans in Arkansas, USA. Application of chemicals and nuclear polyhedrosis virus reduced larval numbers. Pod damage was lowest following insecticide treatment, and was accompanied by a significant yield increase of 280 kg/ha (McLeod et al., 1978).

Studies by Salama et al. (1990) on soyabeans in Egypt revealed that the yield from untreated areas was 1.34 t/ha (64.2%) less than that on the area harvested with insecticide treatments.

The use of Bacillus thuringiensis and an insecticide against S. exigua on maize and sunflowers was also assessed in Egypt. Application of both products resulted in increased yields. B. thuringiensis increased yields to 436.8-495.6 kg/feddan (123.1-160% over the yield in untreated plots) while the insecticide increased yield by 537.6-835.8 kg/feddan (Salama et al., 1993).
Related treatment support
Plantwise Factsheets for Farmers
CABI; CABI, 2018, English language
Son La; CABI, 2013, English language
Vietnam, Son La Plant Protection Sub-Department; CABI, Vietnamese language
Saeed, M.; Ahmad, F.; Hussain, F.; Iqbal, M. F.; CABI, 2014, English language
Saeed, M.; Hussain, F.; Batool, M.; CABI, 2013, Urdu language
 
Pest Management Decision Guides
Cambodia, General Directorate of Agriculture; CABI, 2014, Cambodian language
Wang, B. J.; Liu, C.; CABI, 2016, Chinese language
Ramazani, G. K.; Sanana, J. M.; CABI, 2016, French language
Chandrasena, G. D. S. N.; Gunewardena, K. N. C.; Nimalananda, N. P. H.; CABI, 2015, English language
Cambodia, General Directorate of Agriculture; CABI, 2014, English language
 
External factsheets
AVRDC International Cooperators' Fact Sheets, Asian Vegetable Research and Development Center (AVRDC), 2000, English language
AVRDC International Cooperators' Fact Sheets, Asian Vegetable Research and Development Center (AVRDC), English language
University of California IPM Pest Management Guidelines, University of California, 2008, English language
University of California IPM Pest Management Guidelines, University of California, 2009, English language
University of California IPM Pest Management Guidelines, University of California, 2012, English language
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