|Peach twig borer|
Anarsia lineatella Zeller
-- Jay F. Brunner and Richard E. Rice
Peach twig borer larva in hollow twig (E. Beers, June 2009)
Larva: The larva has a dark brown head and prothorax with distinctive alternating dark and light brown bands around the abdomen. The larva has 4 or 5 instars. A mature larva may grow to 1/2 inch (12 mm) long.
Pupa: The pupa is smooth, brown and does not reside in a cocoon. Pupae are usually found beneath bark scales or cracks in the bark.
Adult: The adult moth is between 1/3 and 1/2 inch (8 to 12 mm) long. It is steel gray with white and dark scales.
Peach twig borer adult
During bloom and petal fall, overwintered larvae emerge from their cells, migrate up the small limbs and twigs and begin to feed on buds and young leaves. As terminal growth develops, a larva will enter a single shoot, boring down the center, causing the terminal to wilt or flag. When mature, the larva leaves the mined shoot in search of a protected place to pupate. Adults from overwintering larvae usually begin to emerge in mid- to late May. Females each lay between 80 and 90 eggs on fruit, shoots or the undersides of leaves next to veins. The eggs, which are laid singly, hatch in 5 to 18 days, depending on temperature.
The larvae can develop equally well in shoots or immature fruit. The first summer generation larvae develop during late May and June. The next adult flight is in early July. During this flight and the following one in late August, moths prefer to lay eggs on maturing fruit. Some larvae that develop from the eggs laid in August go into cells to overwinter. Others continue to develop on fruit and shoots and produce a partial third summer flight of moths in October. These moths lay eggs that produce larvae that overwinter and emerge as moths the following spring.
Larvae of the succeeding generations feed on shoots or fruit. They attack fruit at the stem end, where two fruit touch or where leaves touch the fruit. They also may feed along the sides of the fruit, disfiguring it.
Peach twig borer larval damage (flagging shoot) (H. Riedl)
Peach twig borer larval damage to peach fruit (H. Riedl)
Adult twig borers can be monitored with pheromone traps, which should be placed in orchards by early May to detect emerging moths. Moths in the traps should be counted and removed once a week. Trap bottoms should be replaced after 50 moths have been captured.
Delaying sprays until first summer generation larvae are present can help conserve natural enemies of green peach aphid and improve control of that pest. Larvae of the overwintering generation of peach twig borer do not feed on fruit and, unless numbers are extremely high, cause little economic injury to trees.
A degree-day model can be helpful in timing insecticide treatments against the summer generation of peach twig borer. The developmental thresholds of the peach twig borer are 50°F and 88°F, the same as the codling moth. The same method of calculating degree-days is used so that the degree-day look-up table for codling moth can be used for both species.
Start accumulating degree-days at first moth capture in a pheromone trap. The first moth is captured at 400 to 410 degree-days after March 1. The best timing of insecticide treatments is between 400 and 500 degree-days after first moth capture. The duration of a generation is about 1060 degree-days. If additional sprays are required, they should be applied at 1400 to 1500 degree-days after capture of the first moth of the overwintering generation. A table is available showing the relationship between degree-days after first moth capture and moth flight and egg hatch.