|Fruitworms, armyworms and climbing cutworms|
-- J. Franklin Howell
Green fruitworms and climbing cutworms are closely related moths of the family Noctuidae. Tree fruits are the primary hosts of green fruitworms but only secondary hosts of climbing cutworms. Very few of the more than 150 species of noctuid moths in the Pacific Northwest are tree fruit pests.
Three species of green fruitworms are native to the Northwest: the speckled green fruitworm (Orthosia hibisci), the pyramidal fruitworm (Amphipyra pyramidoides) and the green fruitworm (Lithophane antennata). They are found throughout temperate fruit-producing areas of the United States and Canada. Usually, green fruitworms do not cause extensive damage in commercial orchards that are sprayed for codling moth. They are more often pests in organic orchards or backyard trees. However, they may prove troublesome in orchards where codling moth are controlled by non-chemical methods such as mating disruption.
As green fruitworm infestations tend to recur in the same orchards, historical information is useful for monitoring and developing control strategies.
Green fruitworms and Climbing Cutworms
Green fruitworm egg (H. Riedl)
Larvae: Green fruitworm larvae are caterpillars with distinctive colors and markings. See discussion of green fruitworm species that follow for more detailed descriptions.
Pupae: 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.
Adults: The adult moths are nondescript and are difficult to identify.
Green fruitworm feeding damage to pear (J. Brunner)
Green fruitworms damage buds, flowers, leaves and fruit. Bud damage usually goes unnoticed until it is too late for treatment.
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.
Orthosia hibisci (Guenée)
Speckled green fruitworm larva (F. Howell)
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.
Amphipyra pyramidoides (Guenée)
Pyramidal fruitworm larva (F. Howell)
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.
Lithophane antennata (Walker)
Green fruitworm adult (H. Riedl)
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.
Green fruitworm larva (F. Howell)
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.
Larvae: Larvae of the spotted cutworm, Bertha armyworm and variegated cutworm can be distinguished by their different colors and markings.
Pupae: Pupae of all cutworm and armyworm species are brown and about 3/4 inch (19 mm) long.
Adults: Adults are dull in color but some, like the spotted cutworm and Bertha armyworm, can be identified easily by their wing markings.
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.
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.
Xestia (Amathes) c-nigrum (Linnaeus)
Spotted cutworm adult (F. Howell)
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.
Bud damage by spotted cutworm (F. Howell)
Mamestra configurata Walker
Larva of bertha armyworm (H. Riedl)
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 (Figure 70). 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.
Bertha armyworm damage to pear (F. Howell)
Peridroma saucia (Hübner)
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.