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Prepare for Sod Webworms

I often get calls and emails about "moths" hovering over yards. That is almost always an indicator of sod webworms.

Even if you're not seeing moths, you really should examine sickly looking yards for tiny worms or caterpillars. You could also be experiencing cutworms, especially if you're seeing moths in the evening hours. Sod webworm moths are usually seen only in the early morning hours.

The larvae of sod webworms, and in some cases cutworms, feed on grass blades and can extensively damage turf. The insects can be distinguished through their feeding habits and injury symptoms.

These critters are night-feeding caterpillars, even though the moths are seen at different times. They feed around a small burrow or tunnel in the grass, and they carry blades down into it. Silken threads can be seen in the early morning covering the tunnel.

The cutworm is often found on golf course greens after the grass is aerated. The aeration holes provide an ideal habitat for the larvae during the day, and they feed around the hole at night. Apparently, the moths are attracted to dark-green, healthy turf.

Adult sod webworms are small, white-to-gray moths with a snout-like projection on the front of their heads. While resting, the wings of the moth are closely folded about the body. The females scatter eggs at random early in the morning as they fly over the grass. The eggs hatch in 7-10 days, and the larvae begin feeding on the grass. The first signs of sod webworm damage are areas of unevenly or closely clipped grass and patches of brown. The larvae remain active for several weeks, and then pupate. Adults appear about a week later. Their life cycle is completed in 5-6 weeks with several generations per year.

Sod webworms and cutworms are both readily controlled by most liquid insecticides approved for turfgrass — bifenthrin (goes by Bifen IT & Talstar at retail), malathion or any synthetic pyrethroid or carbamate out there. These are short-residual materials, however, and repeat applications are required to control the next generation. Just as in controlling chinch bugs, three applications of liquid insecticide spread over two weeks usually does a great job of breaking the egg cycle.

If you want to stay organic, and can confirm the issue is cutworms or sod webworms, spray liquid BT (Bacillus thuringiensis) products. Identification is critical, though, when using BT sprays. If, for example, you have chinch bugs, the BT will have no effect, and the problem will just get worse. Organic controls are not really a new type of treatment, and you will find BT in ready-to-spray bottles that just hook on the end of a hose. Years ago, BT liquids were usually only found in concentrates and trigger-spray bottles.

If you take only one thing away from this article, know that you must break the egg cycle by applying the liquid control three times over two weeks.

If you have had sod webworms in the past and want to take preventative steps, you can - and probably should - use a granular version of bifenthrin. The most readily available in our area is Nitro-Phos Bug Out. It is considered the strongest formula on the market with .2% active ingredient. The majority of national brand bifenthrin-based products have as little as .05% and .1%.

By the way, early onset brown patch can also start appearing in July when there’s been an inordinate amount of rain. Many people seem to be somewhat successfully treating the worm problem, but still see growing patches of unhealthy grass. That could be caused by a fungus, so if you think you may have brown patch, treat quickly with any liquid fungicide. Then, do it again in 21 days. If we get really hot and dry, that issue should take care of itself.


IMAGES: Randy Lemmon, manufacturers

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