Billbug larvae (Sphenophorus cicastristriatus) are white, legless grubs with a brown head. They can be separated from white grubs by the complete absence of legs.
Billbugs are grass feeding weevils, or snout weevils. Adults have a distinct, prolonged snout at the tip of which are small chewing mouth parts. Billbugs range from gray to black and the most common billbug of the region (Denver billbug) has distinct double-dash gold markings on the wing covers.
Billbugs apparently do not fly and apparently move to sod farms from adjacent grasses that are also hosts or on infested sod. They can crawl considerable distances. When disturbed they play dead - pulling in their legs and remaining motionless.
The life cycle of the Denver billbug is still incompletely understood. It does differ from that of the bluegrass billbug (Sphenophorous parvulus), a species that is widespread in the eastern half of North America and is present in low numbers in Colorado. The bluegrass billbug has a single generation a year that is synchronized, with only the adult stage surviving winter. Eggs are laid in spring after adults resume activity and there is a peak of larval feeding by bluegrass billbug in early summer.
In contrast, the Denver billbug does not have a synchronized life cycle. Overwintering may occur as larvae in soil or as adults in protected sites on the surface. Some egg laying may occur throughout the growing season. Multiple peaks of feeding may occur - usually in early summer and again in late summer. This may suggest two generations being produced annually or just reflects that generations are not synchronized.
Signficant feeding damage is only done by larvae. Early stages feed within the crown of plants, tunneling and often killing the plant. As larvae get larger they move into the root zone and feed on roots and other plant crowns.
Heavily damaged turfgrass appears droughty. Larval riddling of the plants also cause the turfgrass to hold together poorly so that rolled sod often falls apart at harvest.
The presence of large numbers of billbugs in sod can also lead to rejection of product. Billbugs can damage lawns in residential and commercial sites. However, problems are much more common in sod farms.
There are several natural enemies known to control billbugs and their activities likely are the reason that serious infestations rarely persist at any site. Billbugs are very susceptible to fungal diseases (Beauveria bassiana) and various insect and bird predators feed on them.
Insect parasitic nematodes can be an excellent control of billbug larvae. Both the 'standard' Steinernema carpocapsae and various Heterorhabditis species are effective for control. There are many commercial sources of these organisms.
There is a range in how different Kentucky bluegrass cultivars respond to billbug injury, with some much more tolerant than are others. However, none are resistant to the insect.
Endophytic fungi present in fescues and perennial ryegrass can help control billbugs.
Sod will usually recover from billbug injury, given the care common in sod production. If harvest can be delayed until after a period of peak larval feeding, sod will usually be in good condition for sale and will have few larvae present.
Adult activity can be monitored by pitfall traps - a simple cup sunk with the lip flush with the soil. When used over time this can identify periods of peak billbug activity.
Larvae produce a conspicuous granular material where they feed. When examining the crown and root area of grasses where billbug damage is suspected such material is useful for diagnosis.
Control of the Denver billbug is difficult for several reasons. Larvae present inside plants are not easily reached by insecticides applied to the field surface. Even larvae that have moved to the root zone are little exposed to insecticides that may be bound by the organic matter of the thatch and blades. The only insecticides that can be expected to have effectiveness for control of larvae are those which move in adequate concentration to the root zone. Presently only imidacloprid-containing insecticides (e.g., Merit) can be recommended for control of billbugs in turfgrass.
This can be confusing, as there are several additional insecticides that list billbugs on the label - notably pyrethroids (Talstar, Scimitar, DeltaGard). These labels were developed for control of bluegrass billbug and to be applied to the adult stage of that species. This can be effective since bluegrass billbug emergence in spring is synchronized and a persistent insecticide that remains in the thatch can be used for control. Adult control of billbugs is inappropriate to the Rocky Mountain region since adults of the Denver billbug are present throughout the growing season and many winter as larvae. The pyrethoids and Dursban will not penetrate to the crown/root zone as they have high affinity for organic matter and are not very water soluble. They will not have any effect on billbug larvae.
On the other hand, insect parasitic nematodes can be an effective biological control for billbug larvae. These are microscopic roundworms that penetrate insects and kill them rapidly from injection of bacteria. Both the species Steinernema carpocapsae and various Heterorhabditis species can be used for billbug control. Several suppliers are available in the United States and pricing is variable.
When applying insect parasitic nematodes some special handling and application considerations are important. They are perishable and should be used shortly after receipt. Insect parasitic nematodes are also sensitive to drying and light. Ideally applications should be made very early or late in the day and post treatment irrigation is essential. For more information on insect parasitic nematodes see http://www.ext.colostate.edu/PUBS/INSECT/05573.html
Steinernema carpocapsae, Heterorhaditis bacteriophora, Heterorhabditis megadis and others. Various trade names. Insect parasitic nematodes are typically applied at rate of 100 million to 1 billion per acre. They are living organisms sensitive to UV light and drying. Irrigation immediately after application is essential. Some pretreatment irrigation may also be useful. Applications should not be made during the middle of the day to avoid excessive heat and light. Billbug larvae are typically killed within 3-7 days after application.
Product List for Billbugs in Sod Farms:
Insecticide |
Product per Acre |
Preharvest Interval, remarks |
|
Merit 2 |
1.25-1.6 pt/A |
12 hour reentry. Neonicotinoid insecticide (imidacloprid). Moderate to low water solubility, but will move to crown, upper root zone with irrigation. More persistent than other turf insecticides. Has systemic activity that is expressed in top growth. |
|
Merit 75WP, WSP |
6.4-8.6 oz/A |
12 hour reentry. Neonicotinoid insecticide (imidacloprid). Moderate to low water solubility, but will move to crown, upper root zone with irrigation. More persistent than other turf insecticides. Has systemic activity that is expressed in top growth. |
|
Mach 2 1.5G |
133 lbs/A |
12 hour reentry, 7 days must elapse before harvest. Insect growth regulator (halofenozide) that interferes with molting. Moderate to low water solubility, but will move to crown, upper root zone with irrigation. Fairly slow-acting and may take a week or more to kill larvae. |
|
Mach 2 SC |
4 qts/A |
12 hour reentry, 7 days must elapse before harvest. Insect growth regulator (halofenizide) that interferes with molting. Moderate to low water solubility, but will move to crown, upper root zone with irrigation. Fairly slow-acting and may take a week or more to kill larvae. |
The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality. |
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Categories: Sod, Turf, Insects, Billbug, Sphenophorus cicastristriatus, Denver billbug, Rocky Mountain billbug, New 2004
Date: 04/12/2004