Biological control of turfgrass armyworms with beneficial nematodes

Armyworms: The important insect pest of turfgrass foliage

How to identify armyworms?

Armyworms are easy to identify. Adult moths are light reddish brown in color whereas their full grown larvae/caterpillars are brown in color and having several stripes on their body, and a distinctive “Y” shape mark on the head.

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Life cycle of armyworms:

Armyworms develop through four different stages: Moth, egg, caterpillar (larva) and pupa. Adult moths of armyworm begin emerging from over-wintering pupae early June through early August and start mating. After mating, each female moth lays about 500 eggs in a cluster on the lower surface of the leaves. Under optimal environmental conditions, eggs hatch within one week. After hatching from egg, larval stages starts feeding on grass foliage. While feeding, larvae molts (shed its cuticle) five times, and go through six stages (instars) of development. In the late summer mature, larva falls off the leaves and burrow into ground to form pupa, which survive during winter and life cycle continues. 

Damaging stages of armyworms:

• All the six stages/ instars of caterpillars/larvae of armyworms cause damage to grass or other host plants.
• Adult moths do not cause any type of damage to grasses or other plants.

 

How damage is caused?

All the larval stages cause damage by chewing margins of leaves of all kinds of grasses during night but hide under thatch during day time. Under sever infestation, caterpillars can skeletonize turf plant and reduce the aesthetic value of turfgrass.

Biological control of armyworms:

• Biological control agents including Nucleopolyhedrovirus, parasitoids (Braconid wasps, Apanteles spp. and Tachinid flies) and entomopathogenic nematodes have a potential to manage armyworms.

Why we should use entomopathoegnic nematodes?

• They can kill armyworm larvae with 48 hours after application.
• They are commercially available and easy to apply.
• They are not harmful to children, dogs, cats, personnel involved in its application and beneficial insects like honeybees.
• They do not need a special permission to apply because they are exempted by EPA.

Which species of entomopathogenic nematodes are effective against Armyworms (see literature below)?

• Steinernema carpocapsae
• Heterorhabdtis indica
• Heterorhabdtis bacteriophora

 What stages of armyworms can be targeted?

All the six stages of caterpillars/ larvae are susceptible to entomopathogenic nematodes. Pupae are also susceptible to entomopathogenic nematodes.

What is a recommended dosage of entomopathogenic nematodes required to control armyworms?

•  For the successful control of most of the soil dwelling insect pests, the optimal rate of 1 billion infective juvenile nematodes in 100 to 260 gallons of water per acre is generally recommended (See Table1).

Where you can buy entomopathogenic nematodes?

• All three entomopathogenic nematodes including Steinernema carpocapsae, Heterorhabdtis bacteriophora and Heterorhabdtis indica are sold in our store.
• Steinernema carpocapsae nematodes available both in liquid (sponge-water suspension) and granulated formulations.
• Heterorhabdtis indica and Heterorhabdtis bacteriophora nematodes available only in liquid (sponge- water suspension) formulations.

How long it takes to deliver nematodes?

We can directly deliver entomopathogenic nematodes at your facility in person (service available only in Athens,Georgia) or by UPS throughout US within 3 days after receiving order.

When to apply nematodes

• To target armyworms caterpillars, entomopathogenic nematodes should be applied starting from late June through late August i.e. when young larval (caterpillars) stages (instars) of armyworms are already hatched from eggs (laid in early June) and started feeding on grass leaves.
• To target especially armyworm pupae (to suppress the armyworm moth emergence in the next spring), entomopathogenic nematodes should be applied in late summer when caterpillars starting to fall off from leaves on the ground for pupation.
• Since nematodes are very sensitive to UV light, they will die within a minute or two when exposed to full sun. Therefore, nematodes should be applied early in the morning or late in the evening to avoid exposure to UV light.
• Another advantage of applying nematodes late in the evening is that armyworm caterpillars can be easily targeted because they are generally active and searching for food during night and easily found by entomopathogenic nematodes like Steinernema carpocapsae that uses sit and wait (ambush) strategy to attack its passing by host.  Since armyworm caterpillars are moving actively during night in search of food, they can easily come across to entomopathogenic nematodes like Heterorhabdits bacteriophora and Heterorhabdits indica that uses cruising strategy to finds its host. Because of cruising strategy, both Heterorhabdits bacteriophora and Heterorhabdits indica nematodes can also find caterpillars that are hiding under thatch during day time.

How entomopathogenic nematodes kill armyworms?

After application of either Steinernema spp. or Heterorhabditis spp. on the lawns, their their infective juveniles find armyworm larva or pupa and enter into its body cavity through natural openings such as mouth, anus and spiracles. Once infective juveniles of both Steinernema spp. and Heterorhabditis spp are in the insect body cavity, they release several cells of symbiotic bacteria, Xenorhabdus spp. and Photorhabdus spp., respectively from their gut via anus in the insect blood. Insect blood is conducive for the multiplication of symbiotic bacteria. In the blood, multiplying nematode-bacterium complex causes septicemia and kill their insect host usually within 48 h after infection.

Literature:

• Andalo, V., Santos, V., Moreira, G.F., Moreira, C., Freire, M. and Moino, A. 2012.   Movement of Heterorhabditis amazonensis and Steinernema arenarium in search of corn fall armyworm larvae in artificial conditions.  Scientia Agricola 69: 226-230.
• Ansari, M.A., Waeyenberge, L. and Moens, M. 2007.  Natural occurrence of Steinernema carpocapsae, Weiser, 1955 (Rhabditida: Steinernematidae) in Belgian turf and its virulence to Spodoptera exigua (Lepidoptera: Noctuidae). Russian Journal of Nematology 15: 21-24.
• Kim, J. and Kim, Y. 2011.  Three metabolites from an entomopathogenic bacterium, Xenorhabdus nematophila, inhibit larval development of Spodoptera exigua (Lepidoptera: Noctuidae) by inhibiting a digestive enzyme, phospholipase A (2). Insect Science 18: 282-288.
• Negrisoli, A.S., Garcia, M.S., Negrisoli, C.R.C.B., Bernardi, D. and da Silva, A. 2010.  Efficacy of entomopathogenic nematodes (Nematoda: Rhabditida) and insecticide mixtures to control Spodoptera frugiperda (Smith, 1797) (Lepidoptera: Noctuidae) in corn crops. Crop Protection 29: 677-683.