Cutworm

DAMAGE

• Cutworms are the larvae of several different types of moths.
• Cutworms can cause damage to newly emerged chickpea seedlings, and at times may require insecticide application.
• The first generation of cutworm larvae is the most damaging. Most sever young plants from roots near the soil line as they feed at the base of the leaves; others feed on the roots and underground stems of cut plants. One larva can kill many plants until it pupates in the soil.
• Below-ground feeding cutworms (pale western and red-backed cut worms) cut plants off at or near the soil surface.
• Foliar feeding cutworms (dingy and army cutworms) feed above-ground, consuming the plant foliage.
• The feeding behaviour will vary depending on species, but most feed at night.

LIFE CYCLE

• Cutworms are an early-season insect pest.

• Moths move up from the southern U.S. each spring; females lay eggs on weed and grass hosts in fields or margins. 

• Cutworms overwinter in the soil as pupae. The larvae emerge from the pupae in the spring and feed on new plants.

• The mature larvae are up to 46 mm long, smooth and range from purplish to brown in colour. Patterned with grey lines and spots.

• Adults are 20 mm long body with long, narrow, usually dark forewings which are pale near the tips with three black dashes on each forewing. Wing span varies from 38-50 mm.

• There are one or two larval generations per year before populations die off in the fall.

CONTROL

• Monitor germinating crop for expanding thinned or bare areas.
• Crops should be scouted regularly (weekly) in early spring to June.
• Look for areas with missing plants and wilted, notched, gouged or shot-holed plant tissue. Individual cutworms tend to feed within the seed row, leaving a gap when the affected plants are clipped off or die.
• Scouting for cutworms is often more successful in the evening when they come out to feed. Cutworms are nocturnal and spend the day hiding under debris or in the soil.
• Dig around in suspect areas with a trowel or a shovel. Sift soil or scoop soil into a container and shake loose any potential larvae.
• Cutworms may be found anywhere from just below the soil surface to four inches deep. They move deeper into the soil during the heat of the day, so it may be necessary to dig deeper or revisit the field under cooler conditions.
• Apply necessary foliar treatments in the evening just before larvae emerge from the soil to feed. Only infested areas need to be treated.
• Natural predators include ground beetles that will attack exposed larvae on soil surface; eggs and larvae are attacked by insect parasitoids and predators.

ECONOMIC THRESHOLD

• The economic threshold is one cutworm per metre of row in the top 7.5 cm (3 inches) of soil, when the larvae are still small (less than 2 cm or .79 inches long).

REFERENCE

• Field Crop and Forage Pests and their Natural Enemies in Western Canada:  Identification and Management, Agriculture and Agri-Food Canada, Page 87.

Wireworms

DAMAGE

• Wireworms are the immature stage or larvae of click beetles.
• Wireworms are small-segmented, tan colored worms that live in the soil and will feed on a variety of plant hosts, including field peas, dry beans, lentils, chickpeas, and soybeans. Although wireworms prefer grassy plants (cereal crops), wireworm damage has been noted in other crops including canola, chickpeas, and potatoes.
• Wireworms tend to be more abundant in moist soils and in lower, damper areas of a field.
• Wireworms feed on germinating seeds and on the underground parts of stems of young seedlings, causing reduced crop emergence and thinned stands. Damage is often blamed on poor quality or dry soil, and occurs only in the spring.
• Larvae will migrate near the germinating soil in early spring, and move back down deeper in the soil as soil temperatures climb later in the summer.
• Damage can be seen in the field by wilting plants, resulting from wireworms chewing on the stems, and may appear similar to cutworm damage. The distinction is that wireworm feeding often looks more like the stem is shredded, and it is usually still attached to the roots, whereas cutworm feeding cuts the stem right off. Wireworms tend to shred the plant tissue below the soil surface.
• Wireworms can eventually cause the death of the plant.
• Damage may not be noticed early enough in the season to reseed.

LIFE CYCLE

• Only one generation per year, however the larval stage can last four to 11 years depending on species.
• Both new adults and larvae overwinter. Larvae pupate in earthen cells, and the new adults remain in the cell until the following spring.
• Larvae will migrate near the germinating soil in early spring, and move back down deeper in the soil as soil temperatures climb, later in the summer.
• The mature larvae are elongated, cylindrical, wiry body, 10 – 20 mm long; last abdominal segment is flattened with a keyhole-shaped notch.
• Adult wireworms are click beetles that do not do economic damage to crops. They will characteristically make an audible clicking sound when they try to right themselves when placed on their backs (hence common name – click beetles).

CONTROL

• Controlling wireworm requires the use of an insecticidal seed treatment.
• Predators of wireworms include ground beetles, rove beetles, and larvae of stiletto flies.

ECONOMIC THRESHOLD

• There is no established economic threshold for wireworm in chickpeas and there is no in-crop insecticide available to control wireworm.

REFERENCE

• Field Crop and Forage Pests and their Natural Enemies in Western Canada:  Identification and Management, Agriculture and Agri-Food Canada, Page 33.

Pea Leaf Weevil

Pea Leaf Weevil Emerging from a Root Nodule

DAMAGE

• Pea leaf weevil will feed on chickpeas but is not considered a pest of concern.
• The size of a grain of rice, this non-native invasive insect has emerged in recent years as a threat to Alberta’s field pea, faba bean, and chickpea pulse crops.
• Complicating growers’ pea leaf weevil defense is the fact that this insect appears intermittently, and in some years it’s a significant problem, while in others it’s just a minor inconvenience.
• The grey adult weevil feeds on leaf margins (notching) and growing points of host seedlings.
• Usually chickpea plants will survive this defoliation, however, adult females will lay large numbers of eggs at the base of the plants.
• The main concern is when the larvae hatch and burrow into the soil.  They cause more serious damage by feeding on nitrogen fixing nodules on the roots of the plant, reducing nitrogen to the crop, resulting in poor plant growth and low seed yields.

LIFE CYCLE

• The pea leaf weevil produces one generation per year.
• The adult overwinters in soil within or adjacent to alfalfa, other perennial legume crops, or tree shelters. In May through June, eggs are laid on or near developing chickpea plants.
• In the spring adults disperse, up to a few kilometres, mainly by flying when temperatures are above 17°C or walking short distances. Each female lays up to 300 eggs throughout the summer in the soil near or on developing plants.
• The larvae hatch in one to three weeks, and move to Rhizobium nodules on the root, where they feed.
• Once the larval stage is complete, the insect pupates and emerges as an adult once again in late July through September.
• Newly emerged adults search for any pulse crops to continue feeding
• before overwintering.

CONTROL

• Occasional monitoring to look for the characteristic U-shaped notches on seedlings in early spring is advised.
• Up to the 5th node stage, examine the clam leaf of 10 plants for the notches at each of five sites along the field edge and another five sites within the field when the pea crop is at the second or third node stage. If notches occur on the lower leaves but not on the clam leaf, then the weevil has likely already laid its eggs and it’s too late to spray.
• The proportion of seedlings with terminal leaf damage (ex. leaf notches) provides an adequate indication of overall plant damage, and to some extent, potential yield losses.
• Use seed treatments where pea leaf weevils are a constant threat.  Otherwise, apply recommended foliar sprays against adults as requiring.  Keep monitoring as weevils may re-invade fields.  

ECONOMIC THRESHOLD

• The adult is difficult to observe; therefore, economic thresholds are determined by the severity of notches in the plants at various points of the field – 30% of seedlings with damage (leaf notching) on the clam leaf during the 2nd to 5th node stage.
• The crop is not susceptible to damage after the 6th node stage or it is too late to attempt control.

RESOURCES

• New Video: When Pea Leaf Weevil Attacks!
• Pea Leaf Weevil 2021 Map
• Expansion of Pea Leaf Weevil 2011-2019
• Pea Leaf Weevil
• APG is funding several research projects (Carcamo, Evenden) related to preventing pea leaf weevil damage to crops

REFERENCE

• Field Crop and Forage Pests and their Natural Enemies in Western Canada:  Identification and Management, Agriculture and Agri-Food Canada, p. 30.