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I have marathon grass. It has several bad spots. I’m told by a longtime neighbor, it’s because of yard moths and I need to spray insecticide once a month for grass to grow there. Any suggestions?

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  1. What your neighbor is referring to is more commonly known as "lawn moths" or "sod webworms". The larvae feed on grass and live in the thatch layer of your lawn. Brown spots in your lawn are the result of their feeding. The brown patches will increase in size as the larvae increase in size and in numbers.

    I always recommend an organic or more natural approach before resorting to chemicals. Start by applying Bt (Bacillus thuringiensis), which is an organic, spore forming bacterium that is toxic to caterpillars (and webworms) but not to people, birds and other wildlife. Bt works best on controlling new larvae rather than the more mature larvae. Apply the Bt early in the morning or on a cloudy day. To get rid of the more mature larvae, follow up with a release of beneficial nematodes (available at garden centers and online), which is a biological control for this pest.

    If natural methods are lacking and your infestation more severe, look for a granular insecticide that kills webworms or grub worms, such as Dursban, Sevin, Orthene, or Talstar. Keep in mind that the insecticide will most likely kill the sod webworms' natural predators which include ground and rove beetles, so only use as a last resort.

    To keep future infestations from taking hold, your best defense is a good offense by growing healthy turf: mow high and mow often, irrigating during dry periods (the webworms thrive in drier lawns), control weeds, and fertilize properly. Good luck!

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