Sod webworms

(Question)

I have had lawn damage from these pests in past summers and have recently noted the moth stage. What advice can you give me to control these pests. ( i live in the Toronto

thanks very much

(Answer)

Sod webworms are caterpillars that feed in the thatch on home lawns. The adults are small, tan moths that fly around lawns at night. The caterpillars grow to 2 cm and are tan in colour with dark spots on their backs. They feed in the thatch, causing damage that is similar to grub damage, where areas of turf can be lifted like a carpet. They also leave behind soft green fecal pellets in the areas they are feeding. The damage occurs in September. (Ontario. Ministry of Agriculture, Food  and Rural Affairs).

Your first line of defense is to ensure you are taking care of your lawn.  Water and fertilize regularly to improve the quality of your lawn. Overseed when you see the grass is getting thin. Remove any thatch buildup which can accumulate when you leave grass clippings on the lawn. Mow more frequently to reduce thatch buildup, as shorter clippings biodegrade more quickly.

The moths themselves are not the problem it’s the grubs. Beneficial nematodes are a very effective biological control for use against webworms. “Nematodes search through the soil, locating a host and then enter through natural body openings. A natural bacterium is released that is fatal only to the insect, which dies within 24 to 48 hours. The nematodes reproduce and continue to eliminate grubs as long as soil moisture conditions allow (6 to 8 weeks).

Application should be done when soil temperatures are above 10°C, preferably above 15°C. The lawn must be kept moist for two weeks after application. The solution must be able to penetrate to the root zone area, thus a properly dethatched lawn is advisable. There are no harmful residues left in soil that could contaminate water supplies.  If renovating a turf area after a severe infestation, consider using new cultivars that are resistant to infestations of grubs”. (Posted in: Ask A Master Gardener July 24, 2012).

See also: https://www.torontomastergardeners.ca/askagardener/grey-grubs-in-the-lawn/

Nematodes can be purchased from reputable garden centres and nurseries and even online.  Follow the instructions on package. Although beneficial nematodes can be applied any time larvae are present and soil temperatures are above 12-14 degrees centigrade, late summer and early fall is the ideal time for application. The grub larvae are vulnerable as they are small, thin-skinned and near the surface feeding on grass roots.  You mentioned that you have seen the moths but not grubs, so check the area for grubs before applying nematodes. Hopefully, these tips will help control these nasty pests.