The webworm or “sod webworm” is a common pest for crops such as oats, wheat and corn. While these worms love to feast on crops, their appetite for grassy areas is even more ferocious. These worms are especially destructive to grassy areas such as parks, cemeteries, and golf courses. In its larval stage, the webworm does the most damage to crops and grass. Once the webworm becomes an adult moth, it no longer has a taste for grass or crops of any kind.
If your lawn, landscape, or crops are infested with webworms, you will notice damage around early spring. Damaged areas are characterized by dusty, brown patches that dot the landscape. The brown, patchy grass is an eyesore when compared to normal grass or crops. The webworm feasts for a month or so before fall or early august. While webworms will feast on just about any bed of grass or field of crops, they frequent sunny areas on south facing banks and steep slopes. These areas are hot and dry – which is exactly how the webworm likes it. It is not uncommon for webworms to attack shaded areas, but when faced with a decision to destroy a sunny area or a shaded one, the sunny area will win every time.
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Besides identifying dry, brown patches in order to detect webworm activity, look for thinning areas throughout the grass or turf. A closer look will reveal little green pellets or “frass.” This is the webworms fecal matter. You can also look for webworm adults. They are beige in color and ¾ inches long with a elongated cigar-like shaped body. When at rest on a grass blade, the webworm adult wraps its wings around the body. You will notice two small projections at the front of the moth’s head.
Webworm larvae are typically less than one inch in length and they have dark spots all over the body. Some may have light spots as well. Just a few of the different types of webworms include:
- Bluegrass sod webworm, Parapediasia teterrella (Zincken)
- The cranberry girdler, Chrysoteuchia topiaria (Zeller)
- The larger sod webworm, Pediasia trisecta (Walker)
- The striped sod webworm, Fissicrambus mutabilis (Clemens)
The vagabond sod webworm, Agriphila vulgivagella (Clemens)
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There are many ways to control webworms. You can use cultural controls such as a mixture of fertilizer and water, biological controls such as natural parasites of Bacilus thuringiensis (BT), resistant turf grass varieties, or chemical controls (sprays).
A combination of fertilizer and water will allow the damage to outgrow. Biological controls such as natural parasites (beetles) will control even large webworm populations, if you do not use insecticides. BT (bacterium) can be successful in the early stages of webworm development, but may not be effective when the worms are too big and perennial ryegrasses and tall fescues *(resistant turfgrass varieties) contain fungal endophytes that are resistant to webworm attacks. Chemical controls such as contact or stomach pesticides should be used in the form of a spray. The spray should be administered in the late afternoon hours.
Please note that if you decide to use any chemical controls, you should use them according to the instructions and the laws in your state.