Solution sheet Sod Webworm // The Problem Sod webworms are named after the characteristic silk- or web-lined burrows that the larvae form in the thatch and soil under turf. Sod webworms are a large and diverse family of grass-attacking moths (often referred to as Lepidoptera) that are native to North America. One study found 14 species of sod webworms associated with turf in Virginia. Because of this diversity, we have to make a number of generalizations about sod webworms in this document. The six most important include; bluegrass webworm (Parapediasia teterralla Zinck.), striped sod webworm (Fissancrambus mutabbilis Clem.), silver-striped webworm (Crambus praefectellus Zinck.), larger sod webworm (Pediasia trisecta Wlk.), corn root webworm (Crambus caliginosellus Clem.) and subterranean webworm (cranberry Gilder) (Chrysoteuchia topiaria Zell.). The bluegrass webworm may be the most widespread webworm, causing turf damage from New York to eastern Colorado and south to the border. The larger sod webworm occupies turf in roughly the northern half of the U.S., from coast to coast. The striped sod webworm is widespread east of the Rocky Mountains, especially from Illinois to Tennessee and Pennsylvania. The silver-striped webworm is also widespread over the eastern half of the United States. All six can feed in both cool- and warm-season grasses. The tropical sod webworm (Herpetogramma phaeopteralis Guerne) may be the most common web- worm affecting warm-season grasses. What To Look For Sod webworms feed almost exclusively on grasses, thus all turfgrass species are susceptible to feeding. Small (0.5 inch long with 0.75 - 1.0 inch wingspan), white, gray or tan moths fluttering above the turf while mowing or walking across the turf are usually the first signs of sod webworms, but they are usually not at damaging levels and are not a good diagnostic aid. Moths of sod webworms are unique among other moths because they have relatively long, snout-like moth parts. Moths will also roll their wings into a “tube” around their body when at rest. The exception is the tropical sod webworm that holds its wings like a roof over its body when at rest. Moths of sod webworms do not feed on or otherwise injure turf and are mostly inactive during the day, flying only when disturbed. Most activity and egg-laying are in the early hours after sundown. Sod webworms overwinter as larvae and will emerge and start feeding with warming soils in the spring. Depending on species and location, webworms may have two to five generations per year, and thus can be problematic throughout the growing season. Larval sod webworms are the feeding stage, and they usually feed only on surface layers of leaves and shoots, making physical damage difficult to detect. First symptoms are usually golf ball- to baseball-sized patches that turn yellow to brown in mid-summer. These small patches may quickly expand and coalesce in dry or hot, stressful weather. Bird feeding may also provide additional evidence of substantial sod webworm populations. Careful digging into these patches can reveal silk-wrapped “burrows” in thatch and soil. A soap solution of one tablespoon of dish soap per gallon of water can be poured onto turf where sod webworms are suspected at approximately two gallons/sq. yd. Larvae will usually come to the surface in three to five minutes. Larvae vary in color from black to tan depending on food source, species, and age, but will often have dark circular spots scattered across the body (except corn root webworm and subterranean webworm). Mature larvae are about inch wide and up to 1 inch long. // The Solution The best solution is to plant species and cultivars resistant to feeding where possible. Endophyte-containing perennial ryegrasses, tall fescues, and fine-leaf fescues are good examples where appropriate. Maintaining adequate fertilization and irrigation to maintain growth and potentially outgrow damage is important. Watch for flying adults and carefully investigate any small yellow to tan patches in the turf. Pour a disclosing solution mentioned earlier into suspected areas and larvae should surface within minutes. If damage and/or populations justify control measures, Dylox®420 SL or Sevin® SL can be very effective. In high-value settings or in stressful weather, when even minor damage cannot be tolerated, a quick knock-down product like Tempo® SC Ultra or Tempo WP Ultra will limit damage quickly. Low populations of sod webworms will rarely kill turf since their feeding is usually limited to leaves. However, sod webworm feeding can induce additional stress to lawns during already stressful weather, and thus can compromise the long-term health. Solution1 Rate (per 1,000 sq ft) Rate (per acre) Application Interval Limit applications to no more than 3 per calendar Dylox 420 SL2 4.6 - 6.9 fl oz 200 - 300 fl oz year, minimum retreatment interval of 7 days. Repeat applications can be made up to 4 times Sevin SL3 4.4 - 6.0 fl oz 6.0 - 8.0 qts per year, minimum retreatment interval of 7 days. Reapply if needed, but do not apply Tempo SC Ultra4 0.135 - 0.270 fl oz 6 - 12 fl oz more than 6 times per year. 5 - 10 g Reapply if needed, but do not apply Tempo WP Ultra4 7.7 - 15.4 oz (1 - 2 premeasured scoops) more than 6 times per year. 1See the product labels for complete use instructions. Always read and follow label instructions carefully. 2Do not use more than 16.2 lbs. of AI/A/year. 3Do not irrigate within 24 hours after application. 4Use higher rate for faster knockdown and longer residual. Do not water or mow for 24 hours after application. Close up of sod webworm larvae emerging from soil/thatch Color of sod webworm larvae varies, but most will have dark circular interface. (Bayer) spots scattered across the body. Mature larvae are about 3/8 inch wide and up to 1 inch long. (Doug Richmond, Purdue University) ALWAYS READ AND FOLLOW LABEL INSTRUCTIONS Bayer Environmental Science, a Division of Bayer CropScience LP, 5000 CentreGreen Way, Suite 400, Cary, NC 27513. For additional product information, call toll-free 1-800-331-2867. Not all products are registered in all states. Bayer, the Bayer Cross, Dylox, and Tempo are registered trademarks of Bayer. Sevin is a registered trademark of Tessenderlo Kerley Inc. © 2019 Bayer CropScience LP. ES-818-LL-196-A-R2.