Control sod webworms with beneficial nematodes

Jan 31
Sod webworms: One of the most damaging pests of turfgrass foliage

How to identify Sod webworms?

Full grown larvae/caterpillars of sod webworms are easy to identify as they are about 1 inch long having 4 parallel rows of distinct dark spots along the length of their body and coarse hair distributed all over the body. Also, depending upon species, caterpillars can be gray, brown or greenish in color. Adult sod webworm moths are light, brown or dull ash gray in color.

Life cycle of sod webworms:

Sod webworms develop through four different stages including egg, caterpillar/larva, pupa and adult moth. Sod webworms over-winter as caterpillar in silk-lined tunnels prepared in thatch and/or soil. In the spring, overwintering caterpillars resume feeding on new turfgrass growth, while feeding molts (shed its cuticle) 5-9 times and go through 6-10 stages (instars) of development. Last instar larva pupates inside the cocoons built from soil particles and plant debris in May through June. After 10-15 days of pupation, adult moths emerge from pupae and begin mating. After mating, female moths generally start laying their eggs individually while they are flying and dropping them randomly into the grass. Each moth lays up to 500 eggs during a life span of usually 10 to 15 days. Under optimal environmental temperatures, eggs hatch within 7-15 days. After hatching from egg, larval stage starts immediately feeding on grass foliage. These second generation caterpillars of sod webworms feed through September then overwinter and life cycle continues.

Damaging stages of sod webworms:

All six – ten stages/ instars of sod webworm caterpillars also called larvae cause damage to different grass species or other host plants. Adult moths do not cause any type of damage to any grass species.

How damage is caused?

All the stages of sod webworm caterpillars feed on a variety of grasses. Caterpillars generally chew leaves and stems at the crown of turfgrass causing thinning of grass in small areas. As the infestation progresses, these damaged small areas turn into large brown patches.  When infestation of sod webworms is very high, the damage caused by them is easily noticed as large and irregular brown patches are seen throughout lawns or golf course.  Sod webworm caterpillars feed at night but hide in the silk-lined tunnels prepared by them in thatch and/or soil during day time. The presence of irregular brown patches of dead grass caused by feeding of sod webworm in the middle of a lawn or golf course can reduce its aesthetic value.

Biological control of sod webworms:

Biological control agents including Bacillus thuringiensis (a bacterium which produces a toxin and paralyzes the gut of the caterpillar) and entomopathogenic nematodes also recognized as beneficial nematodes have a potential to manage sod webworms. However, beneficial nematodes have showed promising results in controlling sod webworms.

Why we should use beneficial nematodes?

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

Which species of beneficial nematodes are effective against sod webworms (see literature below)?

  • Steinernema carpocapsae
  • Heterorhabdtis bacteriophora

 What stages of Sod webworms can be targeted?

All the stages of caterpillars/ larvae and pupae can be targeted because both larvae and pupae are susceptible to beneficial nematodes. 

What is a recommended rate of beneficial nematodes required to control sod webworms?

For the successful control most of the soil dwelling insect pests, the optimal rate of 1 billion infective juveniles of beneficial nematodes in 100 to 260 gallons of water per acre is generally recommended (See Table for appropriate amounts of nematodes required for different sizes of sod webworm infested areas to be treated).

Where you can buy beneficial nematodes?

  • Both Steinernema carpocapsae and Heterorhabdtis bacteriophora nematodes are sold in our store.
  • Steinernema carpocapsae nematodes available both in liquid (sponge-water suspension) and granulated formulations
  • Heterorhabdtis bacteriophora nematodes available only in liquid (sponge- water suspension) formulations

How long it takes to deliver nematodes?

We can directly deliver beneficial 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 beneficial nematodes

  • To target sod webworms, beneficial nematodes should be applied starting from early spring through late summer i.e. when young larval (caterpillars) stages (instars) of sod webworms are already hatched from eggs and started feeding on grass leaves.
  • 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 sod webworm caterpillars can be easily targeted because they are generally active and searching for food during night and easily found by Steinernema carpocapsae nematodes that uses sit and wait (ambush) strategy to attack its passing by host.  Since sod webworm caterpillars are moving actively during night in search of food, they can easily come across to Heterorhabdits bacteriophora nematodes that uses cruising strategy to finds its host. Heterorhabdits bacteriophora nematodes can also find caterpillars that are hiding under thatch during day time.

How beneficial nematodes kill sod webworms?

After application of either Steinernema spp. or Heterorhabditis spp. on the lawns, their their infective juveniles find sod webworm 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 sod webworm blood, which is conducive for the multiplication of symbiotic bacteria. In the blood, multiplying nematode-bacterium complex causes septicemia and kill sod webworm caterpillar also called larvae usually within 48 h after infection.

Literature:

Grewal, P.S. Koppenhofer, A.M. and Choo, H.Y. 2005. Lawn, turfgrass and pasture applications. In: Nematodes As Biocontrol Agents. Grewal, P.S. Ehlers, R.-U., Shapiro-Ilan, D. (eds.). CAB publishing, CAB International, Oxon. Pp 115-146.

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