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Lentil – Insects

In general, insects have not been a major problem in lentil production in Alberta. However, in the drier areas of the province, grasshopper and cutworm can sometimes be a problem.

Wireworm occasionally cause some problems, but only if lentil is seeded into a field that has had a forage grass crop included in the rotation. Other insects such as lygus and aphid are occasionally found in lentil but rarely at levels that justify the cost of using an insecticide.

RESOURCE

LINKS

Cutworm

New Pea Seedlings Showing Cutworm Damage

Cutworm, Photo Credit: Canola Council of Canada

DAMAGE
  • Cutworms are the larvae of several different types of moths.
  • Most cutworm damage occurs in late-May and early-June, usually at night, as larvae cut off seedlings just below the soil surface.
  • 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.
  • Cutworms can cause damage to newly emerged lentil seedlings, and at times may require insecticide application.
  • Below-ground feeding cutworms (pale western and red-backed cutworms) 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.
  • Lentil crops can often recover from cutworm damage given favourable growing conditions but maturity may be delayed.

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. Larvae emerge from the pupae in the spring and feed on new plants.
  • The mature larvae are up to 46 mm long, smooth and ranges 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
  • Crops should be scouted regularly (weekly) in early spring to June.
  • Monitor germinating crop for expanding thinned or bare areas.
  • 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.
  • Pheromone traps are available to detect emergence of adults. Monitor for expanding thinned or bare areas, especially sandy ridges and knolls. At a minimum 10 sites, mark off 0.1m2 area (1 ft2) and examine the top 2-3 cm of soil along the edges of the affected areas for larvae. Depending on the crop, other species of cutworms may be present.
  • 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 for cutworms in lentil is 2 to 3 larvae/m2 in the top 7 cm of soil.

REFERENCE

Grasshopper

Grasshopper, Photo Credit: Shelley Barkley

DAMAGE
  • Grasshoppers generally do not favour lentil foliage.
  • Seedlings on the edge of the field can be attacked by grasshopper nymphs as they emerge in the spring.
  • If damage occurs at seedling stage, lentil will usually regrow from buds near or below the soil surface though maturity of these plants will be delayed. With early seeding, lentil will normally grow past the susceptible stage before grasshoppers emerge.
  • Grasshoppers pose the greatest threat from the bud stage through to early pod development as they eat flower buds, open flowers, and developing pods. In this case, yields can be reduced by as much as 90%.
  • Feeding on early developing pods can result in yield loss and cause delay in maturity as the plant tries to compensate for the lost biomass.
  • At harvest, seed contamination with grasshopper parts, specifically heads, can be a problem to clean out as grasshopper heads are similar in size, resulting in grade reduction.
  • Damage from grasshopper feeding is variable. Slight damage to the pods may result in shattering, seed loss, increased risk of disease, and seed staining.

LIFE CYCLE
  • Overwinter as eggs in pods (8-150 eggs/pod) laid in soil and hatch the following spring when the temperature reaches 4.5°C.
  • One generation per year.

CONTROL
  • To monitor, start from a corner of the field, sample at least twenty sites along a line to the field centre, then to one side. Count the number of nymphs that jump in a 1 ft2 area as you approach each site (e.g. every 100 steps). Divide the total number of grasshoppers counted by 2 for number/m2.
  • Check field margins for grasshoppers moving in from roadsides and headland. Numbers will be higher in field margins and a thick lentil crop will deter the insects from moving further into the field as they prefer more open and bare areas. Also check around wet areas in drought seasons.
  • If grasshopper populations only exceed the economic threshold in the field margins, an edge treatment with an appropriate insecticide can save time and reduce costs, while providing adequate control.
  • If control is needed, the optimal timing is when nymphs are at the third instar, which is usually about mid-June. At this stage the grasshoppers become mobile, consume more, and most of the hatch should be complete.
  • Target younger instars in order to use the lowest recommended rates and to reduce the area requiring treatment. 
  • Once grasshoppers reach adult stage, insecticides are much less effective in protecting crops.
  • Several products are available as sprays and baits. Treat only if damage and numbers warrant.
  • Natural predators include birds, small rodents, coyotes, parasitic and predatory insects, as well as the pathogenic fungus Entomophthora grylli Fresenius, and the microsporidian parasite Nosema locustae Canning.

ECONOMIC THRESHOLD
  • Economic control threshold is two grasshoppers per square metre in lentils.

REFERENCE

Pea Aphid

DAMAGE
  • Pea aphids can affect lentil yield and quality when present in sufficient numbers.
  • The pea aphid adult is small, about 4 mm (0.15 inches) long, light green, and long-legged. Adults can develop wings, but are often wingless.
  • The pea aphid weakens the plant directly by sucking its sap, and can also spread viruses from infected plants to healthy ones.
  • Damage caused by aphids can be difficult to quantify because they rob plants of resources by piercing and sucking rather than chewing and defoliating.
  • Populations can increase rapidly due to their ability to give birth to live young without mating, and because they can easily migrate into areas on air currents.

LIFE CYCLE
  • Pea aphids overwinter as eggs on leaves and stems of perennial legumes such as the crowns of clover or alfalfa, but more commonly blow in on warm southerly winds from the United States in June and early July.
  • If the pea aphid arrives early enough and the environment is conducive for rapid reproduction, multiple generations of the insect may eventually result in numbers high enough to cause economic loss.
  • Up to 23 generations are produced asexually before winged females migrate to summer crop hosts where several generations are produced over the summer.
  • Colonies are generally less dense than other species attacking field crops.
  • Winged sexual forms are produced in late summer that mate and females return to winter hosts to lay eggs.

CONTROL
  • Scout for pea aphids at every flower.  At four locations per field, check five plant tips (top 8 inches), or conduct 10 sweeps with a sweep net.
  • Insecticides are registered to control aphids on peas and lentils (refer to Alberta Blue Book (Crop Protection Manual) for appropriate options).  Insecticides with both contact and systemic action can be advantageous. 
  • Heavy winds and rain can minimize the damaging effects.
  • To avoid a reoccurrence of the problem after spraying, delay application of insecticide until late-flowering. One application per season should give satisfactory control.
  • Pea aphid populations usually begin to decline in mid-to-late August due to drying of the crop, parasitic wasps, diseases, and other factors.

ECONOMIC THRESHOLD
  • Control threshold numbers are approximately seven to eight aphids per plant tip. 

RESOURCE

REFERENCE

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

Wireworms

Wireworm, Photo Credit: Shelley Barkley

Prairie Grain Click Beetle, Photo Credit: Shelley Barkley

DAMAGE
  • Wireworms are the immature stage or larvae of click beetles.
  • Wireworms are small-segmented, tan coloured 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 is rarely a problem unless lentil is seeded into a field that has had forage grasses in the rotation.
  • 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.
  • 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.
  • No insecticides are registered for wireworm control in lentil.
  • An insecticide seed treatment should be used for the first two years on cereal crops before lentil is seeded into a field that had forage.

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

REFERENCE

 

OTHER INSECTS

Lygus Bug
  • Because of their wide plant range, Lygus Bug potentially can be found in all pulse crops.
  • Lygus bug can be a pest for lentils in the United States, but has not been a problem in lentils in Alberta to date.
  • The economic threshold for lygus bugs in lentils is seven to 10 adults per 25 sweeps during blooming and podding.
  • To monitor with a sweep net, make 25° to 180° sweeps (with a 38 cm or 15 in net) in at least five randomly selected places in the field.
  • Resource:  Lygus Bug

Adult Lygus Bug, Photo Credit: Shelley Barkley

Fifth Instar Nymph, Photo Credit: Michael Dolinski

Special thanks to Saskatchewan Pulse Growers.