Scaptomyza apicalis
Pest description and crop damage A small fly in the fruit fly family occurs throughout the Willamette Valley in most commercial plantings. Larval infestations cause extensive damage to plant crowns and flower buds. Stand losses and reduced seed yields have been observed in heavily infested fields. Adults are about 3 mm (1/8 inch) long. Body color ranges from drab brown to gray. Eyes are red. Eggs are very small, white, and somewhat elliptical. When flower buds are present, flies insert eggs almost exclusively into these buds. During the vegetative growth stage, however, they will lay eggs in plant leaves, stems, and crowns. Eggs hatch in 7 to 10 days. The larvae are light-colored and about 3 mm long at maturity.
Pest biology A few flies can be found in meadowfoam fields when seedlings emerge in the fall. Beginning in late January, populations increase rapidly. Three or four generations peak from late January through mid-June. Water availability seems to govern adult MFF activity and population size. Few adults are seen from late June through August as fields mature and dry out. Eggs are laid singly anytime adults are active; the peak egg-laying period usually occurs from mid-January through April. The first larvae are usually detected in January in small, yellowish, distorted plants. The number of larvae increases sharply after mid-February and peaks in April. Few larvae are found in plants after bloom.
Scouting and thresholds MFF adults are monitored with unbaited yellow sticky cards. In mid-January, place traps within fields and near field borders. The bottom of the sticky card should be just above canopy height, but high enough to avoid mud splashes in seedling stands. Use approximately one trap for every 3 acres. Inspect traps weekly from mid-January to April. Meadowfoam plants infested with MFF larvae are weak, stunted, and yellowish. A hand lens or microscope often is necessary to see the smaller larvae. Berlese funnels are used to quantify larval infestations. Apply insecticide when average daily fly counts on sticky traps increase from less than one per trap per day to four or more per trap per day. Cold, rainy, and windy weather reduces trap catches even when MFF is abundant: do not underestimate fly counts.
Management-chemical control
Control of larval infestations in individual fields and test plots does not always increase seed yield. Replicated trials indicate a benefit from a midwinter (late February) broadcast insecticide application on fields at risk of heavy infestations. This application reduces significant fly infestations and increases the potential for a boost in seed yield.
The following insecticide labels are for Oregon only.
- bifenthrin (Brigade 2EC) at 0.1 lb ai/A or 6.4 oz. Apply as a broadcast spray at 20 gal minimum by ground, or 10 gal minimum by air. Do not make an application after the bloom begins. Do not apply more than 0.2 lb. ai/A per season. Do not make an application after the bloom begins. Do not graze livestock in treated areas or cut treated crops for feed. Do not apply through chemigation. Oregon only.
- dimethoate (Dimethoate 400) at 0.5 lb ai/A (1 pint) as a broadcast spray.For ground applications, apply in in a minimum of 20 gallons. Aerial application is permitted. Do not apply after crop begins to bloom. 48 hr. REI. SLN OR-050020 (expires 12/31/2023). Oregon only.