- Scientific Name: Sphenophorus (formerly Calendra) parvulus Gyllenhal
- Common Names: bluegrass billbug
- Climatic Zone: temperate
- Geographic Distribution: North America
- Damaging Stage: larva
- Hosts: all cool-season grasses, but avoids endophytic cultivars
- Symptoms: Billbug damage can appear from late June through August. Damage is most severe when summer drought stress is present. Light infestations often produce small dead spots similar to the turf disease, dollar spot. Sometimes the damage appears as irregular mottling or browning in the turf. Heavy infestations can result in complete destruction of the turf by August.
The problem with diagnosis of billbug damage is that it resembles a variety of other turf problems. Turf managers confuse billbug damage with drought, disease, and infestations of chinch bugs, greenbugs or white grubs. Billbug damaged turf turns a whitish straw color rather than the yellow caused by greenbugs. Soil under damaged turf is solid, not spongy as in white grub attacks. Billbug damage on golf courses is often confused with drought stress or sprinkler head failure on tee and bunker banks and other sloped areas. To confirm billbug damage, grasp suspected turf and pull upward. If the stems break easily at ground level and the stems are hollowed out or are full of packed sawdust like material, billbugs are the culprit. Examine the plant crown and roots for evidence of further damage and presence of larvae.
- Description of Stages: Bluegrass billbugs have complete life cycles with a single generation per year and rarely a partial second generation.
Eggs: The pearly white, kidney shaped eggs are inserted into a small hole chewed in grass stems and are approximately 1/16 inch long (1.6 mm).
Larvae: The typical weevil grubs are a robust C-shape with a slightly tapering abdomen. These larvae have no discernable legs and have light yellowish brown head capsules upon hatching. The head capsules gradually darken as the mature larvae reach 1/4 to 3/8 inch (6 mm) in length.
Pupae: The pupae are 3/8 to 1/2 inch (7 to 8 mm) long and are first creamy white. These change to a reddish brown just before the adult emergence. The pupae have the conspicuous billbug snout and pronotum.
Adults: The adults are 1/4 to 3/8 inch (6 to 7 mm) long with a black body. When freshly emerged, the adults are reddish brown. Newly emerged adults have a light brown coating over the body which can be rubbed off to reveal the shiny black shell. The pronotum is covered with small uniform punctures and the wing covers have distinct longitudinal furrows with pits. Occasionally, the pronotal punctures fade along the top midline of the pronotum. Any other patterns indicates that another species may be present. If in doubt, this species should be confirmed by a specialist as several species of billbugs may be present in turf.
- Life Cycle and Habits:
This pest overwinters in the adult stage in most of the Kentucky bluegrass growing regions. Overwintering adults are found in thatch, cracks and crevices in the soil, worm holes and in leaf litter near turf. Adults become active in late April to mid May when the soil surface temperatures rise above 65 °F. The adults wander about in search of suitable grasses to feed. After feeding for a short period of time the female inserts one to three eggs in a feeding at the base of grass stems. Females may continue laying eggs into August but most eggs are laid by early July. In the laboratory, females have been known to lay over 200 eggs, usually two to five per day. The eggs hatch in six days depending on the temperature and the larvae tunnel in the stem. Eventually the larva becomes too large to fit inside the grass stems. They then begin feeding on the grass crowns and later on roots. This is the point at which significant damage to the turf is noticed, especially if little rainfall or irrigation has occurred at this time. After 35 to 55 days, the larvae are full grown and pupate in cells in the soil. The pupae gradually darken and the reddish brown, tineral adults emerge in 8 to 10 days. New adults are most common from late August through September. These do some minor feeding and seek out suitable sites for overwintering. Some adults have been observed trying to fly but no great distances were covered. There is some evidence that adults which emerge early in August may begin laying eggs for a partial second generation. These larvae usually do not mature before fall freezing temperatures arrive.
- Control Approaches
Cultural Control - Use Resistant Turf Varieties - Kentucky bluegrass varieties ‘Touchdown’, ‘Merion’, ‘Nugget’, ‘Adelphi’, ‘Baron’, ‘Cheri’ and ‘Newport’ are susceptible to billbug attack. The varieties ‘Park’, ‘Arista’, ‘NuDwarf’, ‘Delta’, ‘Kenblue’ and ‘South Dakota Certified’ are less susceptible or tolerant to attack. Most perennial ryegrasses and fescues with endophytes are resistant to billbugs. Non endophyte protected ryegrasses and fescues are often attacked, especially when bluegrass lawns nearby are heavily infested. It is strongly recommended that if a lawn must be renovated or overseeded after billbug damage, use bluegrass varieties or a blend containing varieties or species with minimal susceptibility to billbug damage.
Cultural Control - Masking of Damage - Damage from light to moderate billbug infestations can be overcome with adequate irrigation and fertilization. The critical period for irrigation and fertilization is when the bluegrass is preparing for summer dormancy. If a tunneling larva kills the parent plant before the spring-formed daughter plants have completely established roots, the new plants will also die. This lethal stress can be reduced if irrigation is applied at this time. This strategy is a considerable gamble, especially if water is in short supply or home owners are not willing to irrigate.
Natural Control - Fungal Diseases - Billbug adults and larvae are susceptible to the insect killing fungus, Beauveria bassiana. However, this fungus usually does not attack significant numbers of billbugs during dry conditions. Tiny wasps are also known to parasitize billbug eggs.
Biological Control - Insect Parasitic Nematodes - Field tests of products containing insect parasitic nematodes such as Steinernema carpocapsae have shown they can be effective against billbug larvae and adults. Close attention to label recommendations is essential for success.
Chemical Control - Insecticides -
Targeted Treatments. Billbug larvae first feed inside the grass stems and then move to the plant crowns. During this time, they are susceptible to contact insecticides but treatment must be applied before the larvae move down to feed on the roots and rhizomes. Treatments applied after this movement must be irrigated thoroughly. Long residual, systemic insecticides applied in early to mid-May kill young larvae as they begin to feed in the stems.
Curative Treatments. Once significant damage is noticed, most of the billbug larvae have moved into the root and rhizome zones of the turf. The larvae are difficult to reach and insecticide treatments will require thorough irrigation to achieve satisfactory results.
Preventive Treatments. Long residual insecticides applied in late April and early May have been effective in eliminating adult billbugs when they move into the turf for feeding and egg laying. This strategy is often used by lawn care companies in neighborhoods with a history of billbug infestations. These neighborhoods should be routed two to three weeks before the first billbug movement is expected and continued for no more than three weeks after migration is confirmed. Applications of long residual chloronicytinyl or diacylhydrazine insecticides in mid-April to mid-May have been effective in eliminating billbug adults and/or larvae, as well as, provide sufficient residual activity to control annual white grub populations in July and August.
There are several methods to monitor billbug adult activity. The simplest is to place small plastic cups (pit fall traps) inside holes made by using a 4-1/4 inch cup cutter. These can be placed along the turf margin, near flower beds so that they are out of the way. Adults falling into the traps can be easily counted by inspecting them two to three times a week. Another common method is to watch driveways and sidewalks for migrating adults. This works well on warm, sunny days in September but may miss the first Spring activity period by a couple of weeks. Early detection of summer larvae is difficult because they are very small. But, by mid-June, damaged tufts of turf can be pulled out to reveal the characteristic sawdust-like frass left by the larvae. By late June and into July, the larvae are usually large enough to see in the crown, soil or thatch by probing these areas with a knife. Degree-Day Timing
A degree-day model using the average method of calculation, a March 1 starting date and a threshold temperature of 50 F, predicts that the first adult activity should occur between 280 and 352 DDbase50F and the 30% first activity (the time that the last surface insecticide would be effective) should occur between 560 and 624 DDbase50F. Larvae begin to move from the stems to the crowns and are thus exposed to surface insecticides used between 925 and 1035 DDbase50F. They can be controlled from this time until significant visual damage occurs between 1330 and 1485 DDbase50F.
Reliable thresholds have been difficult to establish because of the interrelationship of turf growth habits and the development of billbug larvae. Most Kentucky bluegrasses and fescues establish new tillers in late May and early June. If these tillers establish plentiful root systems, the damage done to the parent plant’s crown is masked. However, if drought conditions occur during this time, the tillers do not establish and the parent plant is damaged. In this case a single billbug larvae can cause a damage spot that appears three to six inches in diameter. During drought conditions, 5 to 10 billbug larvae per ft2 can cause severe damage.