Sod Webworms in St. Augustine Grass: Signs and Treatment

Sod webworms are a development stage of lawn moths. They are caterpillar pests that particularly love St. Augustine grass, which is perfect to feed on and breed in. Lawn moths and brown patches may indicate infestation. So, after identification, how do you get rid of sod webworm?

Mow and water your lawn after identifying sod webworms in the grass to expose most of the pests. Apply a webworm killer such as Bifen IT  or Talstar to get rid of both the lawn moths and their larva. Do not water the lawn for at least 48 hours after treatment for maximum exposure to the pesticide.

While a pesticide like Bifen IT is very effective at getting rid of sod webworms, cutworms, and armyworms, you can also introduce beneficial nematodes or encourage predators like spiders to control their population.

Signs of sod webworm damage in St. Augustine grass

Signs of sod webworms are not very obvious because they feed at night on grass leaves and stems closer to the soil surface. During the day, they hide within thatch, burrows, and their silk webbing. The first identifiable sign of sod webworm attack is the spotting of ragged brown spots in your St. Augustine grass. It looks like a spot with dying grass since the patch will turn brown as the damage becomes extensive.

Here are the signs of sod webworms in St. Augustine grass:

The presence of lawn moths

You’ll see grayish or tan brown-colored lawn moths zigzagging over your St. Augustine grass more at dusk or at night than daytime. While lawn moths (adult webworms) are harmless, their presence should be worrisome because they lay eggs in your turf.

• The eggs hatch into worms (caterpillars)
• Sod webworms feed on grass and cause a lot of damage
• The brown patches should not be confused with fungus in St. Augustine grass.

The type of zigzagging movements that adult moths make in your lawn allows them to scatter their eggs all over your lawn. When they hatch, they eventually cause a lot of damage – patches of discoloration.

Bare patches in your lawn

This will also occur since sod webworms begin to eat some of your grass blades and stems from the bottom (soil surface). This phenomenon will lead to a situation that looks like you have plucked the grass from the root, thus the term scalping. The soil will be easily visible at this point.

Note that the scalping might not be as extensive as the lawn scalping that’s done using equipment.

Brown patches of dying grass

Extensive damage is witnessed when most of your St. Augustine grass looks like it is dying. It starts to show as yellow patches of grass that eventually turn brown when the damage is extensive.

More often than not, sod webworms will leave large patches without grass, especially because sod webworms in large numbers cause more damage. However, sod webworm damage is often confused with heat stress in the summer and even some types of fungal infections.

Fresh grass clippings in the lawn

You can also know you have sod webworm infestation when there are fresh grass clippings. These webworms feed on grass blades in such a way that looks like they are cutting grass. If you haven’t mowed your lawn and there are grass clippings around, look out for sod webworms in the deeper areas closer to the soil surface.

Light green fecal pellets in your grass

Another sign of sod webworm in your lawn is fecal matter that appears to be light green in color. While assessing your grass, check for larvae, webbing, and silk tubes, in which the worms lounge during the day before they come out to eat in the evenings.

You may have to do a close inspection to see if the worms are visible or have at least left small pellets of light green fecal matter in the thatch or on the soil surface.

How to kill sod webworms in St Augustine grass

The best way to get rid of sod webworms is to use an insecticide such as FMC Talstar Pro. Spray the insecticide to control adult lawn moths, the active larvae, and even their eggs. This interferes with their life cycle and helps control the pests for a few seasons.

Here’s how to get rid of sod webworms in St. Augustine grass:

1. Mow the lawn short

The first step to killing sod webworms in your St. Augustine lawn is to trim tall grass. I recommend mowing and bagging the grass clippings to reduce as much cover as possible for the webworm larvae.

Trimming the grass will increase the penetration rate of the insecticide through the grass, which also means greater success in killing the sod webworms. Deep penetration of insecticides ensures the deeply thatched areas (that house webbing) are also dealt with.

2. Water the lawn

Irrigate your lawn with 1/2 to 3/4-inch of water before applying the sod webworm killer. Watering the grass forces the webworms to move closer to the surface as opposed to staying hidden closer to the soil surface where it is not easy to reach them.

The closer they are to the surface, the easier it is for the insecticide to come into contact with them when spraying.

3. Spray the sod webworm killer

The best sod webworm killer is Talstar Pro. Apply the insecticide at a rate of 0.18 – 0.25 fluid oz. per 1000 sq. ft. to get rid of both larval and adult stages of the pest. You can increase the application rate 2-4 times if you are spraying tall grass or heavily thatched lawns.

Depending on the extent of the infestation, you might spot-spay small areas or blanket-spray the entire St. Augustine lawn.

Only apply insecticides when the sod webworms are most in force. Since webworms come out of their silk tubes to feed in the late afternoons and early evenings, it is recommended that you use this time frame to treat your lawn. Sod webworms will be most active at this time, eating away at your grass.

4. Do not water the lawn for 48 hours

For the insecticide to get rid of sod webworms effectively, do not water or mow your lawn for at least 48 hours. If it is very necessary, lightly water the turf with about a 1/8 inch of water.

Some insecticide labels may recommend that you lightly irrigate after applying the treatment to activate the insecticide. Heavy watering washes off the chemical.  

Pro Tip: When choosing an insecticide, investigate the potential damage it can cause on St. Augustine grass. Also, keep in mind that brown patches may appear to be caused by sod webworms, but stress factors and other pests were can also produce such symptoms.

Ensure you also scout for larvae and try counting the adult lawn moths to estimate the number of webworms present.  

Needless to say, the more the lawn moths, larvae, and eggs, the more urgent it is to eliminate them before you have no more St. Augustine grass left. Larvae in particular can become a menace within a very short amount of time.

Here’s a video on the identification and control of sod webworms:

How to prevent sod webworms in your lawn

Integrated Pest Management (IPM) is one of the most efficient means to combat pests on plants. Proper maintenance of a St. Augustine grass patch will keep off all sod webworms since the environment will not be conducive for webbing and laying eggs. Mowing helps keep your grass neat and healthy and makes it easier to quickly identify grass damage, however, small the size.

Prevention works a long way in ensuring your grass remains pest-free. Employing natural pest management tricks is great for avoiding harm to people close by and damage to the larger environment. Chemicals are damaging not only to the grass but also to the soil, air, and humans around.

To prevent sod webworm infestation, consider doing the following tips

Introduce biological sod webworm predators

Introducing natural webworm predators can help reduce the pest population in your lawn as they feed on the adult moths as well as the caterpillars. Encourage larger predatory insects and birds in your lawn and yard to help control their infestations biologically.

Reduce the use of chemical insecticides

Non-selective insecticides cause more damage to your lawn than controlling pests. For example, they can kill wasps, spiders, and other beneficial insects on your lawn.

Cut down on the application of insecticides to allow these natural predators to thrive and kill sod webworms in your St. Augustine lawn.

Mow your lawn regularly

Mowing keeps your grass short and less accommodating to pests like sod webworms. Short grass is not good for webbing and laying eggs. Lawns that are not properly groomed are more susceptible to pest damage and attractive to sod webworms.

The more you interact with your lawn through management, the more likely you are to notice changes that point at the presence of sod webworms. Ensure you keep your grass healthy and maintained so that you do not confuse infestation with anything else.

Will grass grow back after sod webworms?

Grass can grow back after sod webworm damage if the infestation is caught early enough and treated. Keep the lawn well-watered and fertilized to encourage the grass to revive and fill in the bare spots caused by severe pest activity.

It might, however, take some time for the brown patches to turn green again since foliage turnover also depends on the growth rate of the grass and the season.

Sod webworms feed on the leaves thus leading to the death of grass, and the appearance of brown patches in your lawn. When you use proper treatment methods, you will eliminate these pests and provide room for grass regeneration.

Here are great ways to revive your St. Augustine lawn after sod webworm infestation.

• Water and apply fertilizers regularly: Water and fertilizers provide the needed nutrition for the health, growth, and recovery of the grass after pest infestation. You can choose to apply natural or chemical fertilizers to add nutrients to your soil, thus aiding growth of grass.
• Kkeep checking for pests, and applying pest elimination methods. If sod webworms return to your lawn in the process of revival, it will get harder to save your St. Augustine grass the second time round because of fewer and weaker grass blades and stems.

Getting your St. Augustine grass to grow again healthily, might take time. However, what’s crucial is ensuring it doesn’t get re-infested by applying the best sod webworm prevention methods. Sod webworms can be harder to handle when they are in large numbers. Eliminating sod webworms at the slightest sign is key to saving your lawn.

References

• Department of Entomology, Institute of Agriculture and Natural Resources, University of Nebraska-Lincoln: Turfgrass-Sod Webworms  
• Gardening Solutions, University of Florida: Tropical Sod Webworm
• David Smitley, Professor Department of Entomology, Michigan State University Extension: Sod webworm: Tips for your Lawn