Frit Fly

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Frit fly adult resting on tip of grass blade.
Typical frit fly damage to center leaf blade of a stem. (photo: H. Niemczyk)
Frit fly larva (maggot) burrowing down grass stem.
  • Scientific Name: Oscinella frit (Linnaeus) [Phylum Arthropoda: Class Insecta: Order Diptera: Family Chloropidae]


  • Common Names: frit fly


  • Climatic Zone: Temporate


  • Geographic Distribution: A native of Europe but also found across North America. Other species of chloropid flies may infest grasses around the world.


  • Damaging Stage: larvae


  • Hosts: Frit fly has a large host range in the grass family and the larvae commonly infest stems of wheat, oats and rye. In North America, it is known to cause damage to Kentucky bluegrass and bentgrass and occasionally ryegrasses.


  • Damage Symptoms: The common name of this pest is derived from the damage it causes to grasses and grain crops. The larvae (maggots) infest stems and eventually feed on immature kernels within the seed stem. Such heads produce empty kernels of grain called “frits.”

Turfgrass damaged by frit fly maggots has a general yellow (chlorotic) appearance at first. Close examination reveals the central leaf of one or more shoots from the crown is affected, while surrounding shoots and leaves may be green. As feeding progresses, the shoot dies.

The adult fly is an annoyance to golfers on putting greens because they are attracted to white objects, including golf balls and golf carts.


  • Description of Stages:

Like all flies, this pest has a complete life cycle with egg, larval, pupal and adult stages.


Eggs: The translucent shiny cream-colored eggs are slightly bean-shaped and about 1/32 inch (0.4 mm) long.

Larvae: The maggot-like larvae have no legs and no head capsule. However, the anterior end is pointed and has a pair of tiny black hooks used for rasping food. The mature larva is about 3/16 inch (3 mm) long.

Pupae: The pupae formed within a puparium, a light reddish-brown, oval structure that is about 1/8 inch (2 mm) long. Under magnification, ring-like segments can be seen.

Adults: The adult flies are rather undistinguished black flies with yellowish or white markings. They are about the size of the small flies which gather around decaying fruit, approximately 3/32 inch (2 - 2.5 mm) long.


  • Life Cycle and Habits:

Based on Ohio studies, larvae overwinter in a small tunnel eaten out of the grass stem. In the spring, when the grass resumes growth, the maggots feed by rasping inside the stem. As the maggots tunnel downward, they may pass nodes, killing the stem from that point outward. The maggot matures in several weeks and forms a pupa inside the stem or in the duff surrounding the grass plants. The adults live for about one week. The flies can often be seen in considerable numbers resting on the tips of grass blades in the morning or evening sun and are known to alight on lighter colored surfaces such as golf balls or equipment placed on the turf. The new adults insert eggs in the space between a leaf and stem and these eggs take about a week to hatch in warmer weather.

In Ohio, peak adult populations occur in mid-May, late June, late July to early August, and mid-September. There are three to four generations in the northern states and four to five farther south.


  • Control Approaches:

Frit fly is mainly a nuisance on golf courses but the larvae can occasionally build up populations that cause the bentgrass to turn yellow, usually along the collar of greens.

Chemical Control - Adult Frit Fly Control - If the adults are too much of a nuisance for the golfers to tolerate, a general contact insecticide registered for frit fly or fly control can usually eliminate the problem for a week or two. However, if this control is applied just when the first adults are emerging, additional adults will emerge over the next two weeks necessitating an additional application.

Chemical Control - Larval Frit Fly Control - At present, few contact insecticides can reach the interior of infested plants that are hosting frit fly maggots. Use of an insecticide with systemic action is usually a better choice.

Monitoring

Frit fly adults are highly attracted to white objects placed on the turf surface. To see if they are present, place a white handkerchief or white card upon the turf, especially in the afternoon sun. Larval damage is more difficult to detect and monitor. If bentgrass or other grasses begin to appear yellow, closely inspect some of the affected stems to see if the diagnostic yellow central stem surrounded by green leaves is present. Carefully peal back the green leaves to see if a small white maggot is at the base of the yellowing stem.

Thresholds

Each golf course will have to determine when frit fly damage has become unacceptable. In most cases, the damage is considered more of a nuisance.