Pest description and crop damage A small fly in the fruit fly family, occurring 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 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. 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 peaks occur 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 usually are 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. 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.
Control of larval infestations in individual fields and test plots does not always increase seed yield. Replicated trials seem to indicate 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.
- bifenthrin (Brigade) No more than 0.2 lb ai/a per season. Apply pre-bloom 20 GPA. Oregon SLN label 070012. Expires 12/31/2017. Do not make an application after bloom begins. Do not apply more than 0.2 lbs ai per acre per season. Do not graze livestock in treated areas or cut treated crop for feed. Do not apply through chemigation.
- dimethoate (Loveland Dimethoate 400) 0.5 lb ai/a in minimum 20 GPA. Apply pre-bloom when fly is detected. This product is highly toxic to bees. 24C Oregon label OR-0050020. Expires 12/31/2013.
For more information:
Meadowfoam Fly, Oregon State Extension Fact Sheet EM 8760, available from http://extension.oregonstate.edu/catalog