Green Fruitworms

The speckled green fruitworm, pyramidal fruitworm and green fruitworm are general feeders. All tree fruits grown in the Northwest are hosts. Apple is the primary host, followed by pear. Green fruitworms also attack many other plants including crab apple, beech, chokecherry, mahaleb cherry, bird cherry.

The larvae of several Lepidoptera are collectively called green fruitworms because of their general appearance and tendency to damage apple and pear fruit. One species, Orthosia hibisci, which will be referred to as the green fruitworm is currently a serious pest in commercial orchards. It is native to and a pest of deciduous fruits across North America. The larvae feed on a variety of deciduous shade, forest, and fruit trees and shrubs. The GFW has only one generation annually.

GFW adults are night fliers. Their flight closely parallels apple bud development. It begins at about green tip, peaks at tight cluster, and is completed by the pink stage.Females begin egg laying on twigs and developing leaves when apples are in the half-inch green stage. A female is capable of laying several hundred eggs, but normally deposits only 1 or 2 at any given site.

Life cycle:Adults are night-fliers whose flight period closely parallels apple bud development. Flight begins at about green tip, peaks at tight cluster, and ends by the pink stage. Adults are about 2∕3 inch in length. Their forewings are grayish pink, each marked near the middle by two purplish gray spots outlined by a narrow, pale border. The hind wings, not visible when the moth is at rest, are slightly lighter in color than the forewings. Freshly laid eggs are white with a grayish tinge and have numerous ridges radiating from the center. Shortly before hatching the egg takes on a mottled appearance. Newly hatched larvae are ¼ inch long and have a grayish green body with a brown head and thoracic shield. Mature larvae are 1 3∕16 to 1 5∕8 inches long and have a light green body and head. Several narrow white stripes run longitudinally along the top of the body, while a slightly wider, more distinct white line runs along each side. The green areas between the stripes are covered with numerous white speckles. Pupae are dark brown and about 5∕8 inch long.

Females begin egg laying on twigs and developing leaves when apples are in the ½-inch green stage. A female is capable of laying several hundred eggs but normally deposits only one or two at any given site. Young larvae feed on new leaves and flower buds and can often be found inside a rolled leaf or bud cluster. Older larvae damage flower clusters during bloom and continue to feed on developing fruit and leaves for 2 to 3 weeks after petal fall. They then drop to the ground, burrow 2 to 4 inches beneath the soil surface, and pupate over the winter.Most flower buds and blossoms damaged by larvae abort. Most fruit damaged just before and shortly after petal fall also drop prematurely. Some, however, remain at harvest and exhibit deep corky scars and indentations. This injury is indistinguishable at harvest from that caused by the overwintering larvae of the obliquebanded leafroller.

Damage:Most flower buds and blossoms damaged by larvae abort. Most fruit damaged just prior to and shortly after petal fall also drop prematurely. Some, however, remain at harvest and exhibit deep corky scars and indentations . This injury is indistinguishable at harvest from that caused by the overwintering larvae of the obliquebanded leafroller.Young green fruitworm larvae feed on leaves. Fruit feeding usually begins about petal fall and continues until larvae have completed their development. At harvest, these fruit are misshapen and have large, roughened, russeted cavities.Many, but not all apples damaged by green fruitworms abort. Some will remain through harvest and exhibit deep corky scars and indentations. Shown below is some fresh feeding on apple, some older scars on small fruit, and a file photo of damaged fruit at harvest.

Control:The relatively high amount of green fruitworm damage experienced this year is difficult to explain, but it is likely due to higher than normal populations of one or two fruitworm species, and weather conditions that made it difficult to spray this spring. Unfortunately we do not have a representative sample of larvae from affected orchards, so the species responsible for the majority of damage is not known.We do know that windy and wet weather conditions this spring made it challenging to apply pesticides in a timely manner. I am aware of some orchards that did not receive an insecticide before bloom, and then a somewhat later than normal petal fall spray, conditions that clearly would contribute to damage by fruitworms. Most insecticides recommended for prebloom or petal fall applications are effective against fruitworms, as is Sevin applied for thinning.So the timing of applications is generally more important than the material applied, although the insecticide needs to have activity against lepidopteran insects.

The optimum application timing to control green fruitworms is pre-pink to pink, but delayed dormant application of Lorsban is also recognized as a good preventive treatment for fruitworms. It is therefore perplexing that several orchards sprayed with Lorsban at green tip also experienced significant damage. The lesson learned this year’s experience is that if an insecticide cannot be applied at pink, a petal fall spray should be made as soon as possible without jeopardizing the safety of bee populations.

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