Wheat Stem Maggot

Wheat Stem Maggot

Damage by this pest can be severe in some years. Heavy infestations of wheat stands may kill a significant portion of the tillers.

Host Crops

Wheat, rye, barley, oats, bluegrass, millet, timothy, and a range of other native and introduced grass species.


The adult fly is a small (about 5 mm or 1/4 in. long), yellowish-white fly, with bright-green eyes and 3 black stripes across the thorax and abdomen. The larva is as drab as the adult is colourful. Mature larvae are slender, about 6-7 mm (1/4 in.) in length, and pale-green or cream coloured. They look like a fly maggot and are usually found inside the stem.

In cereal plants or grasses, wheat stem maggot larvae overwinter in the lower parts of the stems. The larvae pupate in the spring and the adults emerge in June. After mating, the female flies lay small, white eggs, one per stem, near the sheath of the flag leaf, over a period of 2-3 weeks. These eggs hatch into green-coloured maggots in about 5 days.

The larvae burrow into and consume the interior of the stem, killing the upper part of the stem and the head. They complete their larval development in 18-21 days. There are normally 2 generations per summer.

May June July August September
Overwintering larvae pupate Adult flies emerge, mate, lay eggs Maggots feed, pupate New adults emerge, lay eggs, maggots feed Larvae begin to overwinter

Scouting Techniques

When young tillers are attacked in the fall or early spring, the tillers usually die. The infested plants show the "white head" or "silver top" condition, typically produced by stem-boring insects. The symptoms usually show up in mid- to late June.

The damage is fairly distinctive - white heads without kernels on a plant that is still green. Typically, only 1-5% of the heads are affected and they are usually scattered randomly throughout the field.

The head will pull out with a gentle tug, and usually there is evidence of insect damage (chewing) on the stem above the top node.

Note that root rot infections may produce white heads. However, with root rot, the entire plant turns white. High temperatures and drought stress may also cause prematurely-whitened heads and the death of some spikelets.

Economic Thresholds

No thresholds have been developed for this pest.

Control Tips

Cultural practices like crop rotation and stubble cultivation help to prevent the buildup of populations, especially if done throughout a region. The use of delayed planting is an effective management practice. Destruction of volunteer plants and infested straw is also recommended. There are no resistant varieties for this pest.