Fruitworms, Armyworms and Climbing Cutworms

Green Fruitworms and Climbing Cutworms

(Lepidoptera: Noctuidae)

 

Life stages

Egg

Green fruitworms lay eggs on leaves of the host tree, unlike cutworms, which lay eggs in the cover crop. The egg of a green fruitworm, like that of a cutworm, is almost spherical with a slightly flattened top, a tiny opening in the center called a micropyle, and vertical ribs. The base is flat where the egg is cemented to the plant. It is about 1/30 inch (0.8 mm) in diameter.

Larva

Green fruitworm larvae are caterpillars with distinctive colors and markings. See discussion of green fruitworm species that follow for more detailed descriptions.

Pupa

All green fruitworm pupae are brown and about 1/2 to 3/4 inch (13 to 19 mm long). They are found in the soil or litter in the cover crop.

Adult

The adult moths are nondescript and are difficult to identify.

Hosts

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, hawthorn, rose, quince, almond, blackthorn, strawberry, box elder, sugar maple, red alder, hickory, poplar, oak, currant, willow, birch, aspen and, in Canada, conifers.

Damage

Green fruitworms damage buds, flowers, leaves and fruit. Bud damage usually goes unnoticed until it is too late for treatment.

Monitoring

The following monitoring methods have been developed for green fruitworms in California:

• Take one fruit cluster from at least 100 trees per 20-acre block (or 5 trees per acre) at intervals starting at tight cluster stage and continuing until about 2 to 3 weeks after petal fall.
• Take 50 samples per 20 acres with a beating tray.
• Spend 30 minutes searching for damaged fruit clusters.

Populations are often spotty, so blocks should be covered thoroughly for sampling. If any worms are found, the potential for crop loss is high because this pest can cause severe damage in a short time.

The only way to sample for bud damage is to look in the trees. Ten trees per acre should be enough. If you find bud damage, you then need to know if the damage was caused by green fruitworm or climbing cutworms. Cutworm damage could have been done during the winter before the cover crop grew and there may be no further damage. If it is due to green fruitworms, they are probably still active. If you find fruitworm larvae, you do not need to look for cutworms. Adults can be collected with blacklight traps, in bait pans and by sugaring. For sugaring, soak a sack or cloth in a solution of molasses or brown sugar and beer, fold it into a pad or bandage and place in the tree or around the trunk. Check for moths at night, as they are nocturnal. However, there are no guidelines relating trap catches of adults to damage by larvae.

Biological control

Although a number of parasitic wasps and flies attack green fruitworms, the percentage of larvae parasitized is too small to provide control. Parasitoids attacking green fruitworms include Apanteles, Microplitis, Comedo, Paniseus, Meteorus and Eulophus wasps; Wagneria, Tachinomyia, Wintermia, Campsilura and Ernestia flies; and Mermis (hairworm) nematodes.

Management

Insecticides used to control codling moth appear to control green fruitworms. Bacillus thuringiensis (Bt) may also give some degree of control.
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Speckled Green Fruitworm

Orthosia hibisci (Guenée)

 

Life history

There is one generation per year. The speckled green fruitworm overwinters as a pupa in the soil. Adults emerge from March to May and lay eggs on tree leaves. Larvae begin to hatch in April and climb to the tips of limbs and spurs where they feed and grow. They prefer fruiting spurs and often conceal themselves by webbing the leaves together with silk. They feed at first on buds, then later on flowers, leaves and fruit. In summer, mature larvae drop to the ground and burrow into the soil to pupate.

Life stages

Egg

The egg is pale gray when first laid. It is spherical with a flat base where it is cemented to the plant. It has 40 to 48 ribs and is 1/30 inch (0.8 mm) in diameter. After a day or two, purple blotches appear around the micropyle and the shoulder.

Larva

The larva develops through six instars and measures between 1 and 1-2/3 inches (25 to 41 mm) long when mature. It is green with five white stripes the length of the body (Figure 63). The head is brown at first but gradually turns green.

Adult

The adult is a nondescript, reddish-brown moth about 3/4 inch (19 mm) long.
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Pyramidal Fruitworm

Amphipyra pyramidoides (Guenée)

 

Life stages

Egg

The egg is similar to that of the speckled green fruit worm, except it is a reddish-violet color and has a depressed micropyle.

Larva

The larva is cream colored at first but turns green in the second instar. It has five white stripes. It can be distinguished from other green fruitworms by a dorsal hump at the posterior end which develops in the fourth instar. When mature, the larva is about 1-1/2 inches (38 mm) long.

Adult

The adult is a nondescript brown moth, about 1 inch (25 mm) long.

Life history

The pyramidal fruitworm has one generation per year. It overwinters on the tree as eggs which hatch in April and May. Because larvae do not appear until after bloom, they do not damage buds. Larvae feed primarily on leaves but also eat away patches on the surface of fruit. In June, mature larvae drop to the ground and make cocoons of silk and debris in which they pupate. Adults appear in July and are active until October. Eggs are laid in the fall, either singly or in groups of up to 230.
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Green Fruitworm

Lithophane antennata (Walker)

 

Life stages

Egg

The egg is reddish brown, about 1/30 inch (0.8 mm) in diameter, and has 30 to 36 ribs and a nipple-like micropyle.

Larva

The larva turns from a light cream color to yellow and then to green. In the third instar it develops five white stripes which are less distinct than those on the speckled green fruitworm. During the last two instars it has a prominent white subspiracular stripe which distinguishes it from the speckled green fruitworm. The larva is a little smaller than the other species and is about 1 inch (23 to 28 mm) long when mature. It pupates in a cocoon of silk and debris.

Adult

The adult is gray with hints of blue. The orbicular spot has a partially separated lower loop called the suborbicular spot.

Life history

The green fruitworm has one generation per year. It overwinters as an adult on the ground. Eggs are laid singly or in masses of up to 360 on leaves in spring. Larvae, which are found from April through August, feed on buds, flowers, leaves and fruit. When mature, larvae burrow into the soil to pupate. Adults emerge in the fall.
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Cutworms

The same species can be either a climbing cutworm or armyworm, depending on its behavior, and its behavior often depends on the source of food. Cutworms feed on the roots and shoots of herbaceous plants, and the plant is often cut off at ground level. Armyworms are so named because the larvae often migrate in large numbers to a new feeding area.

Cutworms are found in the majority of orchards in the Northwest, but most species are harmless. Scotogramma trifolii (the clover cutworm), Diarsia pseudorosaria and Leucania sp. are among the harmless species.

The two climbing cutworms that have been the most destructive to tree fruits in the Northwest since the 1970s are the spotted cutworm (Xestia [Amathes] c-nigrum) and the Bertha armyworm (Mamestra configurata). The variegated cutworm (Peridroma saucia), black cutworm (Agrotis ipsilon) and the western yellowstriped armyworm (Spodoptera praefica) seldom cause sufficient damage to warrant treatment.

The spotted, black, and variegated cutworms are found worldwide. The Bertha and western yellowstriped armyworms are found only in the western United States and Canada. Many of the cutworm larvae look alike, so it is easy to mistake a harmless species for a destructive ones.

As weeds are the primary hosts of cutworms, proper weed control in the orchard can help prevent fruit trees becoming infested. Unlike green fruitworm that lay eggs on trees, cutworm moths lay eggs on weeds near the ground. They like dense cover. Larvae spend the days on the soil surface and at night move into trees by climbing tree trunks, drooping limbs, tall weeds, props or stakes. If the trunk is the only pathway, damage is likely to be confined to the lower center of the tree.

General description

Egg

Eggs of cutworms are similar to those of green fruitworms, although they can be as small as 1/50 inch (0.5 mm) in diameter.

Larva

Larvae of the spotted cutworm, Bertha armyworm and variegated cutworm can be distinguished by their different colors and markings.

Pupa

Pupae of all cutworm and armyworm species are brown and about 3/4 inch (19 mm) long.

Adult

Adults are dull in color but some, like the spotted cutworm and Bertha armyworm, can be identified easily by their wing markings.

Hosts

All cutworms that attack tree fruits prefer herbaceous plants. Their preferred host is lamb’s-quarters, a weed that is common in Northwest orchards. Other primary hosts include mustards, plantain, mallow, pigweed, morning glory, Canada thistle and cultivated crops such as potatoes, sugar beets, hops, alfalfa and mint. Tree fruits are secondary hosts.

Damage

Before bloom, look for damaged buds, usually in the low center of the tree. In summer, examine the cover crop, trees and fruit for feeding damage. Buds may be partly or completely eaten. Larvae feed from the edges of the leaves, often eating most of the leaf. Larvae often follow trails they make from the ground to their feeding sites on the tree, so damage is often confined to a few stems or limbs, while nearby stems or limbs are undamaged.

Monitoring

Monitoring is similar for all cutworms. It is not practical to sample for eggs, as they are too hard to find among the weeds. Instead, monitor for damage, larvae or adults.The larvae are nocturnal and hide in the soil or under stones and debris during the day. To find them, carefully sort through an area of soil and debris at the base of the tree. One or two areas of 1/2 square yard (0.5 square meter) are probably enough. Larvae are generally at the depth where the soil becomes moist. If there is debris on the ground, keeping the soil surface moist, the larvae remain at the surface. Traps also can be used to catch larvae. The most effective and simple is a board, 8 by 12 inches (20 by 30 cm), or heavy shingle placed on the ground near the trunk of the tree. A rock should be placed on top to hold it snug to the ground or debris and prevent it being blown around by the wind. Leave the trap for a few days, then lift it up and count the larvae that are sheltered beneath it. Adults can be monitored with blacklight or pheromone traps, although reliable treatment thresholds have not been established. If enough food is available in the cover crop, a large number of larvae could be tolerated, otherwise even a small number could be damaging.

Biological control

Cutworms have many natural enemies. Insects, spiders, birds and rodents all prey on cutworm eggs, larvae and adults. Rodents are good predators but can also damage trees. Predators and parasites, together with good weed control, will usually keep cutworm populations in check.

Cutworm populations are often greatly reduced by a viral disease. Spotted cutworms and Bertha armyworms that are infected by a virus climb to the top of a plant or branch to die. They attach themselves by their legs and hang from the plant. The skin turns black and everything inside liquifies. When the skin breaks, the liquid drips out. The liquid full of virus runs down the plant. Insects feed on the liquid and spread the virus.

Management

Good cover crop management is the most effective way to control cutworms. Eliminating weeds removes egg-laying sites and their preferred food. Mowing discourages egg laying and encourages predation. It also exposes eggs so they dry out and do not hatch. Insecticides can be used to control cutworms. However, the different species of cutworms differ in their susceptibility to these products so it is important to know which species is being treated. Spotted cutworm and Bertha armyworm cohabit, which can complicate control. Spray only the tree trunk and the area under the trees. Keeping chemicals off the tree canopy will allow predators and parasites to survive.
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Spotted cutworm

Xestia (Amathes) c-nigrum (Linnaeus)

 

Life stages

Egg

The egg is a pinkish flattened sphere, about 1/40 inch (0.6 mm) in diameter with 29 to 35 ribs. Eggs are often laid singly on fescue or in clusters on broad-leaved weeds.

Larva

The larva develops through seven instars. The first instar is whitish with a dark head. The second, third and sometimes the fourth instars are green with three indistinct white stripes. The larva then turns brown, and black triangles appear on the seventh to ninth abdominal segments. The mature larva is brown with gray flecks and is 1-1/4 to 1-1/2 inches (30 to 36 mm) long. There may be triangles on all abdominal segments, but they tend to be paler on the forward segments. Usually it has a light subspiracular stripe tinged with yellow or orange.

Adult

The adult moth is a dark gray-black and has a distinct pyramid-shaped orbicular spot in white bordered with black and a brown reniform spot with a white border. These markings make it easy to identify.

Life history

There are two generations in the Pacific Northwest. It overwinters as a larva in the soil. Adults of the first generation are active from May into July. Second generation adults are active from August into October. Eggs can be found all summer long on the ground or cover crop. Second generation larvae overwinter in a cold torpor, rather than diapause, and can become active and feed on warm days during the winter when the temperature reaches 40 to 50ºF.

Damage

Larvae often feed before cover crops have begun to grow in the spring, making fruit buds particularly vulnerable. Bud damage ranges from small round holes on the side of the bud to fully eaten buds. Normally buds are half eaten. Spring is when they cause the most damage. Before applying controls, make sure the damage is fresh. It is possible that feeding on buds will have stopped and there will be no further damage. Later in the year, larvae feed mainly on leaves and can defoliate young trees. However, they may also damage fruit and often excavate holes large enough to conceal their entire bodies.
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Bertha Armyworm

Mamestra configurata Walker

 

Life stages

Egg

The egg is white when first laid but within 24 hours develops brown markings around the micropyle and the equator. It has about 38 ribs. Eggs are laid on the cover crop in batches of 100 to 150 in neat diagonal rows.

Larva

The larva develops through six instars. The first four can be shades of gray, brown or green with five broken white stripes. The later instars generally turn brown with conspicuous yellow stripes often flushed with orange. No matter what the basic color, the larva always has black patches down the center back which help distinguish this species. When mature, the larva is about 1-1/4 inches (30 mm) long.

Adult

The adult moth is gray with a black-green background color. The green fades after it dies. The orbicular wing spot is gray or gray-brown with a black border and the reniform spot is white, making this moth easy to identify.

Life history

The Bertha armyworm has two generations overlapping those of the spotted cutworm. It overwinters as a pupa in the soil. Adults begin to emerge in May. Eggs are laid on the cover crop from late May until October. The first generation overlaps the second. Larvae are most numerous in late June and in late August and September. Bertha armyworm inflicts most of its damage in the fall, as there are no larvae in the spring.

Damage

Where weed control is neglected, the Bertha armyworm can defoliate young trees. Newly hatched larvae damage only the surface of fruit, but older larvae excavate large holes. Young larvae skeletonize leaves and older larvae consume the entire leaf except for the mid-vein.
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Variegated Cutworm

Peridroma saucia (Hübner)

 

Life stages

Egg

The egg is white with a reddish coloring around the equator and micropyle. It is about 1/50 inch (0.5 mm) in diameter and has 35 to 50 ribs.

Larva

The larva goes through six instars that vary from gray to dark brown. A mature larva of this species can be distinguished easily by 4 to 7 distinct pale yellow spots, one per segment, down the middle of the back. Usually, it has a narrow orange-brown spiracular stripe and irregular orange and yellow markings.

Adult

The adult moth is a nondescript rusty brown color. The orbicular spot is often distinct. The reniform spot is darker but not obvious. This moth is less easy to identify than the spotted cutworm and the Bertha armyworm.

Life history

The variegated cutworm overwinters as a larva in the soil. It does not go into diapause to overwinter and many larvae do not survive. This may be one reason variegated cutworm populations rarely reach damaging levels. Surviving larvae may damage buds early in the year. Larvae pupate in the soil and adults begin to emerge in the spring. Adults fly and lay eggs from April through November.

Damage

Larvae are in the orchard throughout the year but usually do not become numerous until fall. Populations are seldom high enough to cause economic damage.