Armyworms - Identify, Control and Kill These Nasty Pests

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by Max - last update on December 29, 2018, 8:35 pm
Armyworms

Any keen gardener knows that armyworms are one of the most destructive pests that your plants or lawns can encounter. Much like an army troop, they travel in large groups, targeting one plant at a time and quickly destroying it before methodically moving along to the next plant.

They can take out a whole crop with remarkable speed, demonstrating how they earned their apt name of armyworm. Leaving very little behind, armyworms can completely skeletonize their victims, causing huge problems for farmers as well as professional and hobby gardeners.

Quick Facts

OriginOrigin varies between species
Common NamesFall armyworm, True armyworm, Southern armyworm, Northern armyworm, Beet armyworm, Lawn armyworm, Rice ear-cutting caterpillar, Oriental armyworm, Nutgrass armyworm, African armyworm
FamilyBelongs to Noctuidae
Scientific NamesSpodoptera frugiperda, Spodoptera exigua, Spodoptera exempta, Spodoptera eridania, Spodoptera mauritia, Mythimna unipuncta, Mythimna separata
IdentificationVarying distinctive features dependent on species, including: Grey/green with long dark stripes running the length of body. Green/brown with three long pale stripes and a darker head. Black/green with dark red head. Brown with yellow stripes. Green with long dark stripes along upper sides. Pale green with brown and white stripes
Plants AffectedLawns and wild grasses, Sugarcane, Wheat, Fruit and vegetable crops, Tobacco, Rice, Rye, Rapeseed, Corn, Cotton, Many flowering plants
RemediesDiatomaceous earth, Beneficial insects, Neem oil, Bacillus thuringiensis var. kurstaki, Pyrethrin sprays

Where Do Armyworms Come From?

Armyworms, in their different species, are present on all continents, excluding Antarctica. Some are more prevalent and widespread than others. For example, the true armyworm can be found throughout South America, western Asia, southern Europe, Africa, and in the United States east of the Rocky Mountains.

The southern armyworm, true to its name, is more commonly found in South America, the southern states of the U.S., and the Caribbean while the northern armyworm inhabits Japan, China, Australia, and New Zealand.

The fall armyworm, unsurprisingly, makes its appearance in the fall throughout the Americas. It has recently migrated to Africa where it is causing devastation to food crops, threatening to worsen the already poverty stricken third world countries. There is real concern that, as the fall armyworm can travel up to 60 miles per night, they could reach Europe.

Similarly, the beet worm, originated in Asia but has since spread over the globe and can now be found worldwide. The African armyworm, meanwhile, has stayed partially true to its name and is mostly found in Africa and Asia.

The lawn armyworm, as its name suggests, ravages lawns, leaving large dead patches of grass in its wake. The lawn armyworm predominantly resides in Australia, India, and the Pacific Islands.

Identification

An armyworm coils on a leaf
An armyworm coils on a leaf

Armyworms are the caterpillar-like creatures that are the larval phase of a moth’s life cycle. Their coloring varies between species, but they are generally between twenty and forty millimeters in length with many tiny legs hidden under their bodies, and sometimes a furry look about them.

In trying to identify an armyworm, you should always inspect your plants in the early morning or right before dusk as you will not see any armyworm movement during the day. Inspect the under leaf of your plants as well as newly emerging rolled leaves and cracks in the soil where armyworms like to hide.

To correctly identify whether you have an infestation of armyworms, and which species you have, first consider which species are typically found in your location and then match up your armyworm with their usual markings.

True/Common Armyworm

The common armyworm is a green-toned brown in color with white stripes along each side, which are bordered with thin orange lines. The common armyworm also features a yellowish orange colored head, and is smooth-bodied in the absence of hairs. The distinctive markings that differentiate this type of armyworm from other armyworms is its four large dark spots on the underside of its body.

Northern Armyworm

The northern armyworm is regularly confused with the common armyworm as they have very similar markings. Similar to the common armyworm, the stripes and patterns on a northern armyworm become more distinctive as they grow in size. (Queensland Government- Department of Agriculture and Fisheries).

Fall Armyworm

Fall Armyworms
Fall Armyworm - Source: University OF Nebraska–Lincoln

The fall armyworm is predominantly pale brown and is flanked by darker stripes down both lengths of the body. The male of the species tends to have more striking patterns than the females. The head of the fall armyworm features a white marking in the shape of an upside down ‘Y’ as well as a spotty pattern to each side of the head.

Southern Armyworm

The larvae of southern armyworms are dark green with a brownish red head. Each side of their body typically features a yellow or white stripe running along its length. (University of Florida- Entomology and Nematology).

African Armyworm

The African armyworm has a mottled body that can vary in color from green to brown. It features contrasting stripes along its length (Infonet Biovision).

Types of Armyworm

There are many different types of armyworm with each type then being categorized into different species. The fall armyworm alone has as many as 53 different species that have been identified. Of all species of armyworm, it is estimated that at least half are agricultural pests.

Life Cycle of an Armyworm

Armyworm moths lay their eggs in clusters on their chosen food source - usually leaves or blades of grass. The eggs, which are oval and less than 0.45mm at their longest point, are pale green when they are first laid and turn to a tan brown color as they reach maturity at around four to six days.

Armyworm eggs hatch into armyworm larva, which is the form of the pest during its most destructive phase. The larvae grow to around 30 to 4mm in length during this stage, which lasts between 14 and 20 days.

The larvae then pupate in the soil for between 11 and 13 days before breaking out into a moth that will live for up to two weeks. During its life as an adult moth, it will lay around 1000 eggs, beginning the cycle again.

What Do They Eat?

Armyworms have different preferences for food depending on their type and species.

Common armyworm: Eats predominantly barley, oats, wheat, and grasses (Queensland Government- Department of Agriculture and Fisheries)

Northern armyworm: Feasts on wheat, maize, rice, and barley

Lawn armyworm: Prefers to eat lawn grass and wild grasses, including nut grass, Bermuda grass, orchard grass, McCoy grass, para grass, as well as barley, oats, and wheat. They will also strip other plants of their leaves, including beans, cabbage, and kale

African armyworm: Host plants are typically varieties of rice, maize, carrots, sugarcane, ginger, barley, wheat, and sorghum. If they cannot find their preferred food source, they will also feed on plants in the palm family. Wild grasses where the African armyworm can also be found include Bermuda grass, Guinea grass, and Quickgrass (Infonet Biovision)

Fall armyworm: Eats around 80 different crops, including vegetables, rice, maize, cotton, and groundnuts (Source). The broad menu from which the fall armyworm likes to feast is what makes it so threatening to crops, particularly in Africa where the armyworm has recently migrated, and the farmers are not accustomed to managing them

Southern armyworm: Found on many different plants, including weeds and vegetable crops. Their host plants include cabbage, avocado, pepper, tomato, sweet potato, and sunflowers

Damage & Symptoms

Leaves eaten by armyworms
Leaves eaten by armyworms

Armyworms feed primarily on foliage, and when young will feed with vigor, often skeletonizing leaves. For this reason, if an infestation is moderate to severe, the presence of armyworms will be fairly obvious.

Damage will be seen on leaves, grass, and any soft foliage on plants and crops in the form of holes. Older armyworms, as they gain strength, will even root into the fruit and flowers of a plant or the hard husks protecting wheat or corn. The damage on fruit or vegetables will be evident with the armyworm having burrowed itself into the crop.

Other symptoms can include large areas of dead grass, or bald patches in a lawn.

Armyworm Control

Physical Control

Physical controls have their place in home gardens or small farms, but will have little effect on larger spaces infested with armyworms.

If you spot armyworms on your plants, remove them from their hosts and put into a jar of boiling water to kill them.

Remove any affected plants from your garden, and do not compost them.

Wash all gardening tools and equipment to reduce the spread of the armyworm infestation.

Covering plants in lightweight white fabric may also help to deter moths from making a home in your garden.

Keep weeds and wild grasses near your plants and crops to a minimum. These are ideal homes for armyworms and will encourage them to inhabit your land.

Encourage beneficial insects and birds to nest in your garden. Crows, frogs, spiders, flies, bats, and parasitic wasps are all natural predators of the armyworm and will discourage armyworms from making their home in your garden. You can plant herbs such as dill and coriander to attract the beneficial bugs.

Biological Control

Bacillus thuringiensis var. Kurstaki, also known as BT, is a highly effective bacterium that will paralyze the digestive system of an armyworm. It can be bought in liquid form and sprayed over infected plants.

Pyrethrin is a natural pesticide made of dry crushed flowers and water. It can be sprayed onto armyworms and will paralyze them on contact.

Neem oil, made from the extract of neem leaves, is another natural pesticide effective in controlling armyworms. It can be sprayed on affected plants and will restrict their growth.

Diatomaceous earth is a dust like substance which features extremely sharp particles. For the armyworm, this would be like crawling through lots of tiny razor blades, and will shred them on contact.

Prevention

Prepare your land in a way that will expose and remove armyworms. Clean up and debris at the end of each crop season.

Weed your land often. Weeds and grassy areas are ideal homes for armyworms.

Plant crops early.

Strategically grow plants around your crops that will encourage the presence of beneficial insects. This will help to deter or keep any armyworm population in check.

Continuously check your plants for armyworms. Infestations are often not caught until the problem is severe, by which time treating the issue becomes harder and will need to be done on a larger scale. Scouting out armyworms earlier will make removal easier and will save the destruction of your plants. Be sure to look for armyworms in the early morning or evening as they are not active during the day. Check the underside of leaves where eggs are usually visible in clusters as well as new growth where armyworms can be hiding inside unfurled leaves.


Conclusion

Armyworm infestations can range from mild to severe, even compromising the food source of a community as we have seen in Africa with the recent migration of the fall armyworm. They are a fast-spreading pest, and therefore it is useful to keep a check on your plants so that if an armyworm is spotted, you can act quickly before your entire garden is destroyed.

The armyworm, despite its appetite for destruction, can be managed with relative ease as long as you take the necessary steps to eliminate them from your plants. Simple ideas such as planting flowers or herbs that attract natural predators of the armyworm can be easily achieved, and may be enough to discourage the harmful critters from making a home amongst your plants. Natural pesticides have also proven very effective in the management of armyworms, meaning that strong chemical solutions are rarely necessary.

Armyworms - Identify, Control and Kill These Nasty Pests

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