Annual Bluegrass Weevil
- Scientific Name: Listronotus (formerly, Hyperodes) maculicollis (Dietz)
- Common Names: annual bluegrass weevil, Hyperodes weevil
- Climatic Zone: Temperate
- Geographic Distribution: Listronotus anthracinus has been collected only east of the Mississippi river but the Listronotus causing turf damage has been localized in Connecticut, the Long Island area, Massachusetts, New York, Delaware, Pennsylvania, northern West Virginia and eastern Ohio.
- Damaging Stage: larvae kill stems, adults chew on leaves
- Damage Symptoms: Highly maintained Poa annua in greens, aprons, tees, fairways and tennis courts is attacked. Light infestations cause a slight yellowing and browning of the turf. Moderate infestations cause small irregular patches of dead turf and heavy attack kills turf in large areas. Damage begins to become obvious in late May or early June and is often mistaken for disease or environmental problems. Hollowed out grass stems and leaf notching are diagnostic characters.
- Description of Stages: This pest has a complete life cycle (eggs, larvae, pupae and adults) with the larvae being typical for weevils, a C shaped legless grub.
Eggs: The eggs are oblong, about 3/64 inch (1 mm) long and change from yellow to smokey black when about to hatch.
Larvae: The larvae are crescent-shaped, legless and have a creamy white body. The head capsule is light brown in young larvae but becomes darker in older larvae. Newly hatched larvae are about 3/64 inch (1 mm) long and grow to about 3/16 inch (4.5 mm) when mature.
Pupae: Pupae are 1/8 to 3/16 inch (3.5 to 4.5 mm) long and are located in cells constructed within the soil. The snout, wing covers and legs are evident on the surface of the pupa. They are first a creamy white, turning reddish brown just before the adult emerges.
Adults: Adults are 1/8 to 3/16 inch (3.5 to 4.0 mm) long and have the combined length of the snout and prothorax distinctly shorter than the length of the wing covers. This is different than billbugs which have combined snout and prothoracic lengths equal to the wing cover length. This Listronotus is black with the wing covers coated with fine yellowish hairs, yellowish scales and scattered spots of grayish white scales. Newly emerged adults (callow adults) are orange brown in color and require several days before becoming fully pigmented.
- Life Cycle and Habits: This pest overwinters in the adult stage in protected areas near places Poa annua is cultured. They prefer to hide in tufts of bunch grasses and under leaf litter around bushes and trees. These adults become active in early spring, usually in April, and seek out actively growing Poa annua. Here, the females chew small holes through the lower leaf sheaths and deposit from one to nine eggs; usually two eggs are laid per stem. The eggs take four to five days to hatch and the young grubs chew their way into the stems. Once inside, the larva burrows up and down the stem, feeding on the soft tissue inside and leaving tightly packed sawdust like frass behind. This early feeding may not kill the stem but the leaves turn yellow and gradually wither. The larvae may move from stem to stem, hollowing out the centers until they are too large to fit inside. At this time the larvae feed externally, especially at the crown. The five larval instars are passed in three to four weeks and the fully developed larva digs about 5 to 10mm into the soil to form a earthen pupal cell. This cell is formed by the circular wiggling of the larva which packs the soil. The cell formation takes three to four days and the pupa remains in the cell for five to seven days before molting into the adult form. The freshly emerged adult is light colored, soft and remains in the pupal cell for five to six days to harden before emerging. These light colored adults are called callow adults. The entire cycle takes 25 to 45 days depending upon food and temperature. The mature adults hide during the daytime but come to the tips of the grass stems to feed at night. This feeding continues through July and early August. The adults then seem to disappear, apparently going to their overwintering sites. There is some evidence that a few of these summer feeding weevils lay some eggs in August and September but most wait until the following spring.
- Control Approaches:
Cultural Control - Reduce Overwintering Sites - Remove leaf litter adjacent to fairways, especially needles under white pine as well as other conifers. These sites are where the overwintering adults accumulate.
Natural Control - Predators and Parasites - Few natural controls appear to exist for this pest though natural parasitism by a common soil inhabiting nematode, Steinernema spp., has been observed.
Biological Control - Insect Parasitic Nematodes - Commercial formulations of the insect parasitic nematode, Steinernema carpocapsae, applied when the larvae are feeding at the base of the plants, has provided 70% or more control. To achieve this level of control, carefully follow the label instructions concerning application and posttreatment irrigation.
Chemical Control - Insecticides -
Curative Treatments The curative approach to control damage from this pest has not been as effective as preventive methods. Rapid acting insecticides should be applied when the larvae are feeding at the bases of the plants and followed with sufficient irrigation to move it to this target site.
Preventive Treatments Application of selected contact insecticides during the third week of April, when overwintered adults return to annual bluegrass to begin egg laying, has successfully prevented first generation larval infestations. This application should coincide with the full bloom of Forsythia to first bloom of common flowering dogwood.
Annual bluegrass blades bearing characteristic crescent-shaped notches is a good indicator of annual bluegrass weevil adults. Examining the tips of grass blades for adults at night with a flashlight is also useful.
The earliest recognizable symptom of larval damage is yellowing of the central stems and leaves of the grass plant. Upon close examination with a 10X hand lens, evidence of larval tunneling or the small larva itself may be seen.
Symptoms of damage are often first seen on the edges of greens, tees and fairways. Yellowing usually spreads as the season progresses. Damage is most obvious during May and June. Examination of the thatch and soil in heavily damaged areas reveals larvae, pupae and light brown adults. The hand lens is useful in detecting the characteristic U-shaped notches made by the larvae at the bases of stems.