The 1, 2, 3 of Sod Webworm – DO NOT PANIC!!!

Posted on 28. Aug, 2019 by in Lawn Care

Unfortunately, we have just seen our first case of Sod Webworm. Fortunately this time we are a lot more familiar with these very hungry caterpillars and have the experience and tools to handle this without chem bombing the neighborhood.


These pests DO NOT kill your grass on their own. They eat the blades leaving exposed runners and thatch that make the grass appear dead or dying.

Sod Webworm causes varying degrees of damage depending on the conditions and health of your grass. They appear to favor shaded and wet areas. A healthy lawn is capable of hosting Sod Webworm with little or no long term damage. Even in areas of stress they can sometimes be managed with organic measures ie. composting, correct watering and mowing practices – no insecticide required.


See below the 3 things you should know if these little beasties visit your lawn.

1. What To Look For.

  • Primarily the moths flying around the grass and ground cover. It is normal to see a few moths in your yard, but when it becomes ten, twenty or even a swarm you may see some damage.
  • Areas of grass that are inexplicably shorter than others and may appear thinner.
The side effects of herbicide may initially look similar so if possible keep a note of when and where your last weed treatment was.
  • You can look for the caterpillars (flush them out with a mild soapy water to get them moving) but if you have the moths and damage then you can safely assume you have Sod Webworm.
  • Bite marks on blades – Sod Webworm literally eat the grass. Initially, this will present as discoloration on the side of blades but as the caterpillars grow they will take mouthfuls (think shark bite out of surfboard!)



2. Do Not Panic!

  •  When Sod Webworm came along 3 years ago we hadn’t seen them in over 30 years. Across the City, chemical insecticides were applied at an alarming rate out of fear we would all lose our lawns, (and we were one of the guilty parties) in hindsight we now believe that the over-application of chemical insecticides killed off the Sod Webworms natural predators and exacerbated the problem.

3. What To Do/Not To Do


  • Do assess and monitor your lawn. Sod Webworm can move fast but remember they do not kill the grass on their own, whether you are seeing moths, damage or nothing at all look at your lawn now (take pictures if it helps) and monitor regularly. Consult a professional if you are unsure but continue to monitor your lawn – there is no substitute for regular monitoring especially as we head into the most stressful time of year for lawns
  • Do apply a layer of organic compost over the affected area.
  • Do apply beneficial nematodes as soon as the temperatures are low enough (probably October) then every one to two years to maintain protection.
  • Do consider incorporating more organic measures to your lawn treatment program. The repercussions of Sod Webworm outbreak of 2016/17 was what prompted me to create the Hybrid Organic program that many of our customers are now on. These lawns have already proved more resilient against many grass diseases and pests.
  • Do purchase a worm/caterpillar specific liquid insecticide (we recommend Monterey BT) for use if the damage starts to move rapidly or grass is eaten down to the runner, I strongly recommend that everyone considers carefully before applying any kind of insecticide or chemical to their lawn but it is good to be prepared.

Do Not:

  • Do not use a weed-eater or oversized mower on the affected area, grass healthy or otherwise should be cut at 3″ with a residential push mower.
  • Do not rake the affected area
  • Do not apply a chemical that has not been recommended by a professional or been used successfully in the past on your grass.
  • Do not over-water the area.
  • Do not allow any exposed runners to dry out (the compost will help with this.)

Is Your Lawn High Risk?

Some lawns are more likely to be affected more seriously than others. If your lawn has had any of the following you may need to take preventative measures.

  1. Lawns already damaged from other causes.
  2. New grass
  3. Lawns recently treated with a chemical insecticide, especially in the last 2-4 weeks.
  4. Grass that cannot be monitored regularly.
  5. Lawns with high shade or drainage issues.
YOU WILL CONTINUE TO SEE MOTHS. No matter what measures are taken you are likely to see more and more moths as time passes, but remind yourselves it is the caterpillars that do the damage and trying to control flying insects is like trying to control your neighbors Doveweed 🙂 I firmly believe a healthy lawn is the best protection against any damage the caterpillars may inflict. 





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