By: Mary H. Dyer, Credentialed Garden Writer
Tropical sod webworms in lawns do extensive damage in warm, tropical or sub-tropical climates. They usually don’t destroy turf unless infestations are severe, but even minor infestations can cause problems for lawns that are already stressed by hot, dry weather.
Signs of Tropical Sod Webworms in Lawns
The pests, which feed exclusively on grass, are the larvae of small moths that you may notice flying around your lawn when disturbed by walking, watering or mowing. The moths themselves don’t cause any problems, but they lay their eggs in the surface of the soil. It’s the larvae that eat the blades of grass and create tunnels in the thatch.
The larvae overwinter in the thatch, then begin feeding on your lawn when the weather gets warm in spring. The pests multiply quickly, producing three or four generations in a season.
The first symptoms of tropical sod webworms in lawns, other than the appearance of the moths, include small patches that turn yellow or broth by midsummer. Sunny, dry areas are most susceptible, and the pests aren’t usually found in shady spots.
The damage spreads quickly, especially during hot, dry weather. Soon, the grass thins and becomes uneven and ragged. You may also notice thin webbing when the grass is dewy.
Birds feeding on your lawn more than usual are a good sign of pests, and they are a big help when it comes to tropical sod webworm control.
How to Manage Tropical Sod Webworms
Controlling tropical sod webworms in the landscape consists of good maintenance. Care for your lawn properly; well-maintained turf is less susceptible to damage. Water and feed regularly, but don’t over fertilize, as fast growth may contribute to the infestation.
Mow regularly, but don’t scalp your lawn. Set your mower to 3 inches (7.6 cm.) and your lawn will be healthier and better able to withstand problems, including pests, drought, heat and other stresses.
Pour a mixture of 1 tablespoon dish soap and 1 gallon of water onto infested patches at a rate of about a gallon per square yard. You’ll see larvae coming to the surface in a few minutes. The soap should kill the pests, but if not, destroy them with a rake.
Bacillus thuringiensis (Bt), a natural soil bacterium that works well as a pesticide, usually kills pests and has fewer harmful side effects than chemical products. Repeat every five to seven days
Use chemical pesticides only as a last resort and only when you’re absolutely sure webworms are present, as toxic chemicals often create more problems by killing beneficial insects. Use products labeled for tropical webworms and don’t irrigate for 12 to 24 hours.
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Adult sod webworms, called lawn moths, are typical snout moths: they have sensory appendages called labial palps that extend in front of the head. The moth holds its wings close to and over its body at rest, giving it a slender appearance. When disturbed, the moth makes a short flight close to the grass. At night, these moths drop their eggs indiscriminately onto turf. The creamy larvae have a distinctive double row of brown or black spots down their backs, located at the base of long bristles. The Lucerne moth larva is somewhat larger than the other sod webworm larvae. During the day larvae reside in silk-lined burrows, writhing when disturbed. At night they emerge to feed.
Bluegrasses and bentgrasses often suffer the most damage, while perennial ryegrasses and turf-type tall fescues infected with endophytes (symbiotic fungi) and warm-season turfgrasses are more resistant.
Garden Help: Tiny moths mean you probably have sod webworms
As the summer progresses, so do the many ailments afflicting our lawns. One of the major pests we’ve been seeing pop up lately is the tropical sod webworm.
The tropical sod webworm (Herpetogramma phaeopteralis) is one of a complex of caterpillar pests of our lawns, which also includes the fall armyworm (Spodoptera frugiperda), fiery skipper (Hylephia phyleus) and the striped grass looper. These webworms can be pests on all of our common lawn species, including St. Augustine, Bermuda, bahia, centipede, zoysia and seashore paspalum.
In the northern portions of the state, we often encounter outbreaks of this pest from August through October, though they can be found throughout the warm season. They generally will not survive our winters but instead migrate back from the southern portions of the state, where they persist year-round.
Knowing a pest’s biology is one of the first steps in identifying the most appropriate methods to manage it. Adults of the sod webworm feed on nectar and can be found hiding in protected areas during the day, such as within the canopy of shrubs, ornamentals and at transitional zones with natural areas. The adults of this species are most active during what is called the crepuscular period, basically that period of time while the sun is setting or rising. Particularly during the evening the adult moths can be seen flying in a “zig-zag” pattern across the lawn. As they across the lawn in this manner, they’re actually depositing clusters of eggs on the leaf blades. From there it will take 3 to 4 days for the eggs to hatch and for the young larvae to emerge.
The adults don’t actually cause any direct damage to the lawn it’s these larvae that cause us the issue as they feed voraciously while developing through a total of six larval stages. That development period can last from 21-47 days, during which lawn damage is occurring. The older the larvae get, the harder they become to control. It usually takes some time for their damage to bother us enough and by that time the lawn is starting to look rough.The good news is most lawns can recuperate from this damage if it’s otherwise been cared for appropriately and the outbreak is addressed in a timely manner.
So what kind of damage do the larvae cause and what should you be looking for in order to catch them early? The youngest larvae, up to the fourth instar, are still fairly small and often feed in a manner that allows their damage to be missed it’s called window-feeding and this is where only the epidermal layer of the leaf is being eaten. This results in leaves that are browning out, generally near the tip, but the leaf remains intact. This is that critical time that you really need to identify them before they grow large. The initial damage may be noticed simply as an area of lawn that is a little shorter than the rest or with a ragged appearance. That ragged appearance can really look very similar to how your lawn looks if mowed with a dull blade. Once the larvae get older, though, they’ll start consuming entire sections off of the leaf blade and as their size increases so does the amount they’ll consume. Those last two instars are where the significant damage starts to occur, and unfortunately that’s usually when they finally get noticed.
The larvae are night-feeders, so if you go out during the day you likely won’t see them grazing on your lawn. However, there are some scouting techniques you can use to confirm their presence. These will be found particularly in the hotter and drier, full-sun sections of the lawn. When you find a suspected patch you can search through the leaf and thatch layers and look for the larvae, webbing or insect frass on the leaf blades. The larvae may be deep into the thatch or upper-layers of soil but you’ll see their web tunnels.
Another method is to do a soil drench with soapy water. Use ¼ cup of lemon-scented dish soap in two gallons of water and pour it over a 1-2 square-foot section where the infestation is suspected. After a few minutes the larvae will be clambering up the leaf blades to avoid the irritation caused by the soap. Generally, when populations exceed 15 larvae per square yard then implementation of a chemical control strategy is warranted.
How can you manage these? Keep your lawn fertilizer and irrigated properly. Healthy lawns will tolerate light populations without much aesthetic losses. Heavy irrigation or fertilization will increase your pest pressure through lush tender growth and thatch buildup.
If you start seeing the adults you may consider bagging the lawn clippings during that period and composting them away from the lawn. Mowing can often remove a fair portion of the eggs if it’s conducted regularly.
Another critical management practice is to keep the thatch layer under control. The more thatch you have, the more you open up the lawn for a whole range of pests and diseases.
Once populations reach your control threshold, there are both biological and chemical control options that can be employed. Bacillus thruigniensis var. kurstaki (Bt.k) is a biological control method that can be very effective if applied early while the larvae are still first or second instar. Otherwise products containing azadiractin, carbaryl, chlorantraniliprole, clothianidin, pyrethroids or spinosad can also be effective, but keep in mind the same thing that often encourages population buildup (thatch) will also limit the effective coverage of these compounds.
If you have a professional managing your lawn, understand that most accounts are on a monthly rotation so get out in your lawn, enjoy it and observe. Keep an eye out for these pests and let them know if you see something so they can treat it in time. If the infestation has been raging for 3-4 weeks, it can still be controlled but the damage will already be done! As always, scout regularly for best results.
Have horticulture questions? For specific recommendations on chemical controls reach out to the Master Gardener Volunteers at your local county extension office. Contact information for your county can be found at sfyl.ifas.ufl.edu/find-your-local-office/.
Chris Kerr is an environmental horticulture agent with the Duval County Extension Service and the University of Florida/IFAS.
Sod webworms are rampant across the Houston area right now and many customers have asked us how to permanently get rid of these pests. Not sure what sod webworms are or what trouble they might cause your lawn?
Take a walk across your yard near your flowerbeds during the day. If you see off-white moths that take flight and then settle back into your shrubs or sheltered areas, it’s probably sod webworm moths. It’s easy to assume that brown grass could be related to high temperatures instead of insects during the summer months however, these pests can rapidly cause significant damage within days. For professional identification, bring a 6”x6” grass sample (with 2” of attached soil) to our garden center and we will be happy to assist with a diagnosis.
Sob webworms life cycle: overwinter, pupate in late spring, and then adults emerge. Eggs are laid mid-summer, and two to three generations of sod webworms could be completed in a year. Adult moths don’t directly cause damage to lawns, but their offspring certainly take their toll. Larvae feed primarily at night, chewing off blades of grass. You can imagine the damage your lawn could sustain very quickly if the cycle isn’t broken.
These pests can be particularly difficult to get rid of and lawn damage occurs rapidly therefore, if you’re seeing these moths in your lawn or suspect an infestation, immediate treatment is recommended for the best result of recovery. If you’d like professional treatment through our Warren’s All-Ways Green program please contact our landscaping office at 281-354-7111 for more details.
To effectively treat Sodweb Worms yourself, Warren’s Southern Garden and Kingwood Garden Center both have treatment bundles available. The treatment process is as follows:
- Granular bifenthrin
- Liquid bifenthrin or Cyonara (applied after granular helps water it in)
- Liquid BT (Organic caterpillar & webworm control)
- Liquid bifenthrin or Cyonara
- Liquid BT (Organic caterpillar & webworm control)
- Liquid bifenthrin or Cyonara
(Repeat full treatment as necessary)
We also recommend the following tips:
- Spray in the late afternoon or evening when they are more active.
- Spray every 7-10 days to break the egg cycle (multiple treatments).
- Give your lawn an extra boost by applying Heirloom Soils of Texas Leaf Mold Compost in the damaged areas.
- Spray with Medina HastaGro Lawn Fertilizer (or similar product recommended by our knowledgeable gardeners) to repair and restore your lawn.
Unfortunately, there are no conclusive ways to prevent sod webworms from invading your lawn. They are aggressive pests and well suited for our region. For more helpful tips on sod webworms or to speak with our garden experts, stop by one of our Garden Centers or give us a call at 281-354-6111.
Tropical Sod Webworms
Damaged turf from tropical sod webworm activity
It’s finally fall in South Texas. The temperatures are a little cooler, there’s more rain in the forecast, and you may be thinking “Finally, my lawn will get a break from a summer of unbearable heat.” We hope that’s the case, but with warm-weather turfgrass, especially St. Augustine, be on the lookout for tropical sod webworms. These caterpillars, like their relative the fall armyworm and cutworms, are destructive pests to newly laid sod and established lawns.
After their eggs hatch, tropical sod webworm larvae begin to feed on turfgrass leaves at night or during overcast parts of the day. It is at this phase in the lifecycle when they are most destructive to lawns and can cause a tremendous amount of damage in just a few days. In addition, with a 28-day lifecycle, several generations of these webworms can be produced in a single season.
Larval tropical sod webworm caterpillar
Look for these signs to identify tropical sod webworm activity in your lawn.
- Affected areas in the lawn will have shorter turf than unaffected areas
- Leaf blades may have a notched appearance due to webworm damage
- Areas next to shrubs or flower beds may show the first signs of damage since the webworms rest and lay eggs in these areas
- Use a soapy water mixture of one tablespoon of lemon-scented dish washing liquid in one gallon of water to flush caterpillars out to the soil surface for identification