Apple-Apple maggot

Rhagoletis pomonella

The apple maggot is a small fly native to the northeastern United States and Canada, where it originally fed on hawthorn. It was not until 100 years after apples were introduced to North America that it was found feeding on apples, and today it is a key pest of apples in northeastern regions, where several insecticide sprays are necessary to produce fruit free from maggot injury and contamination. It has since migrated to the PNW, where it was originally found in Portland in 1979. By 2000 it was found in most western Oregon and Washington counties. It apparently can survive in a wide range of climatic conditions. The apple maggot remains a potential threat to the Northwest apple and pear industry. The maggots develop in apples, quince and the fruits of native and ornamental hawthorn. The apple maggot also may occur incidentally in pear, plum, and tart cherry. Fortunately, the apple maggot seems to attack only apple and hawthorn in Oregon and Washington, and so far has not been found on pear. Early cultivars of apples are particularly susceptible to damage. There is a quarantine on the movement of fruit in Washington and Oregon counties known to have this pest. Check with your State Department of Agriculture for details.

Pest description and crop damage The adult is a fly about the size of a housefly. The body is black, with dark red eyes, and the thorax and abdomen have distinctive white or cream bands. The wings are banded with black. The larva is cylindrical, tapering to a pointed, nondistinct head, and is white except for two dark mouth hooks. The pupa appears similar to a large, dark brown grain of wheat. Eggs are small, white and smooth, but are rarely seen, as they are laid under the skin of host fruit.

The larvae tunnel through the fruit, leaving a brown, threadlike, irregular trail. The tunnels enlarge as the larvae grow. The tunnels serve as entry points for decay organisms, which cause internal rotting. Fruit of soft-fleshed, early maturing varieties often drop prematurely. In hard fleshed, late maturing varieties, internal decay may not occur until after the apple drops.

Biology and life history The maggot spends the winter in the soil as a pupa. As the soil warms, it begins to develop, and in June, the adults begin to emerge. Emergence continues through the summer, and flies are active until October. The adults feed on honeydew produced by aphids or other insects, and after 7 to 10 days mate and lay eggs. Eggs are laid singly under the skin of an apple, causing a small, brown, decayed area to develop. Eggs hatch in 2 to 10 days, and larvae commence tunneling through the fruit. Development is completed in 20 to 30 days, at which point the fruit often drops to the ground. The larvae then leave the fruit and burrow into the soil to pupate. There is usually only one generation per year.

Scouting and thresholds The most effective monitoring method involves the use of sticky traps, either yellow or red. Yellow sticky cards baited with ammonium carbonate chargers are effective. Hang traps in the outer third of the canopy by mid June. Inspect regularly. A phenology model of this pest can be used to predict first emergence of flies and is available from uspest.org.

Management-biological control

Because the larvae are protected inside the fruit, little effective biological control has been observed.

Management-cultural control

Backyard sanitation is one of the most effective management strategies for home orchards. Regularly inspect fruit while it is on the tree, removing and destroying any insect-infested fruit. Destroy infested fruit: if fruit is left on the ground, maggots will continue to develop in them and then pupate in the soil. Pick up and destroy fallen apples at weekly intervals from early August until harvest. In home orchards, traps can be used to manage low density fly populations. Place one apple maggot trap in each small apple tree (less than 8 feet tall), two to four traps on medium-sized trees, or six to eight traps on trees 20 to 25 feet tall. Clean traps weekly and replace adhesive every 3 weeks. This technique is not effective against high fly populations.

Management-chemical control: HOME USE

Apply first in early July.

  • acetamiprid
  • azadirachtin (neem oil)-Some formulations are OMRI-listed for organic use.
  • carbaryl
  • esfenvalerate
  • gamma-cyhalothrin-Highly toxic to bees.
  • kaolin clay-Applied as a spray to leaves, stems, and fruit, it acts as a repellant to some insect pests. Some formulations are OMRI-listed for organic use.
  • lambda-cyhalothrin
  • malathion
  • pyrethrins-Some formulations are OMRI-listed for organic use.
  • zeta-cypermethrin

Management-chemical control: COMMERCIAL USE

Spring and summer

  • acetamiprid (Assail 70WP) at 3.4 oz/a in up to 100 gal of water per application. Do not make more than 4 applications per year or exceed 13.5 oz/a per growing season. PHI 7 days. [Group 4A]
  • beta-cyfluthrin (Bathyroid XL) at 2.4 to 2.8 oz/a in no less than 100 gal of water per application. PHI 7 days. REI 12 hr. [Group3]
  • chloranthraniliprole (Altacor) at 3.0 to 4.5 oz/a in no less than 100 gal of water per application. Do not apply more than 9 oz/a per growing season. Do not apply more than 4 applications per season. Do not use an adjuvant within 60 days of harvest. PHI 14 days. [Group 28]
  • clothianidin (Clutch 50WDG) at 2 to 3 oz/a in up to 100 gal of water per application. Do not apply more than 6.4 oz/a per growing season. PHI 7 days. [Group 4A]
  • cyfluthrin (Tombstone) at 2.4 to 2.8 oz/a in no less than 100 gal of water per application. PHI 7 days. [Group3A]
  • gamma-cyhalothrin (Declare) at 1.02 to 2.05 oz/a in enough water to achieve full coverage. PHI 21 days. [Group3A]
  • indoxacarb (Avaunt) at 5 to 6 oz/a in up to 200 gal of water per application. Make no more than 3 applications prior to hand-thinning. No hand thinning after the 4th application. Make no more than 4 applications per growing season. Do not apply more than 24 oz/a per growing season. For use in low- to moderate-pressure situations, with alternate control measures such as mating disruption. PHI 14 days. [Group 22A]
  • kaolin clay-Applied as a spray to leaves, stems, and fruit, it acts as a repellant to some insect pests. Some formulations are OMRI-listed for organic use.
  • lambda-cyhalothrin (Warrior II, generics available) at 1.28 to 2.56 oz in enough water to achieve thorough coverage. PHI 21 days. [Group 3A]
  • spinetoram (Delegate WG) at 6 to 7 oz/a in up to 100 gal of water per application. Do not exceed four applications or 28 oz/a per season. PHI 7 days. [Group 5] [larvicidal]
  • spinosad (Entrust 80WP or 2SC) at 2 to 3 oz or 6-10 fl oz /a in up to 100 gal of water per application. Do not exceed 9 oz or 29 fl oz /a per season. PHI 7 days. [Group 5] [larvicidal] OMRI-listed for organic use.
  • thiacloprid (Calypso) at 4 to 8 oz/a in 300 gal of water per application. Maximum of 16 oz/a per year. PHI 30 days. [Group 4A]
  • zeta-cypermethrin (Mustang Maxx) at 1.28 to 4.0 oz/a in a minimum of 100 gal of water for dilute spray. PHI 14 days. [Group 3A]