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Dry Beans – Insects

The following show the most common insect pests of dry beans. Insects of concern in dry beans include below-ground feeders, sap feeders, as well as defoliators. Crops should be scouted throughout the growing season to monitor for damage, and control measures only taken if economic thresholds are reached to help protect beneficial insects present in the field.

LINKS

Alfalfa Looper

Alfalfa Looper, Photo Credit John Capinera, University of Florida, Bugwood.org

DAMAGE
  • Alfalfa loopers are occasional pests of dry beans and are more common when grown near alfalfa.
  • Adult loopers feed on nectar from flowers and are active during the day. They may defoliate and clip flowers resulting in yield loss.
  • The first generation larvae feed along leaf margins and may defoliate a large portion of the plant as well as clip flowers and seed pods.
  • Infestations are usually patchy and during flowering.
  • Second generation larvae are usually not a problem (see below).

LIFE CYCLE
  • Loopers either overwinter in the soil as pupae, or adult moths get blown up from the United States in early summer.
  • Generally, there are two or three generations per year and they may overlap as some may overwinter and some blow in.

CONTROL
  • Control measures only taken if economic thresholds are reached to help protect beneficial insects present in the field.

ECONOMIC THRESHOLD
  • There is no economic threshold established in dry beans, however other crops recommend control when populations exceed 15 larvae per metre squared, and heavy defoliation and flower clipping occurs.

REFERENCE

Aphid

Pea Aphid, Multiple Life Stages, Photo Credit: Whitney Cranshaw, Colorado State University, Bugwood.org

DAMAGE
  • A variety of different aphids can be present in many crops.
  • Occasionally, pea aphids can become a significant pest of dry beans.
  • Aphids rarely overwinter in Alberta, although occasionally some eggs may survive, attached to crop residue in alfalfa and clover fields.

LIFE CYCLE
  • Adult pea aphids are 3 mm long, light green, with long legs, and can be wingless or have translucent wings.
  • Depending on weather conditions there may be from 7 to 15 generations per season, and if conditions favour multiple generations, then populations may increase to levels where control is warranted.

CONTROL
  • Control measures only taken if economic thresholds are reached to help protect beneficial insects present in the field.
  • Natural pests such as the lady bird beetle, minute pirate bug, damsel bug, syrphid fly larvae, and a number of parasitic wasps can help control populations.
  • In warm moist weather a fungal disease can also affect aphids.

ECONOMIC THRESHOLD
  • There is not established economic thresholds for this pest.

RESOURCE

Grasshoppers

Grasshopper, Photo Credit: Shelley Barkley

DAMAGE
  • Grasshoppers feed on the foliage of almost any crop, dry beans included.
  • Field edges usually have higher infestations as they move in from field borders. Significant defoliation and yield damage can occur, especially if the other crops surrounding have matured and the dry beans are still immature, which increases migration of grasshopper populations to the field.
  • Seedlings on the edge of the field can be attacked by grasshopper nymphs as they emerge in the spring.
  • 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% and cause delays 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 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.
  • Target younger instars in order to use the lowest recommended rates and to reduce the area requiring treatment. The nympths molt through five nymphal instars before becoming adult in three to seven weeks.
  • 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.
  • 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

REFERENCE

LYGUS BUG

Adult Lygus Bug, Photo Credit: Shelley Barkley

Fifth Instar Nymph, Photo Credit: Michael Dolinski

DAMAGE
  • Lygus bugs are not often a significant pest of dry beans, however, if the weather is hot and dry it can favour the buildup of populations and increase the potential for damage to early growth.
  • Lygus bugs feed on plant sap and have piercing, sucking mouth parts.
  • If heavy feeding occurs, they can disrupt flower set and cause pod abortion.
  • Direct feeding on maturing beans can cause surface pitting, with the potential to affect the quality of the beans.
  • Nymphs tend to be more problematic than adult lygus bugs.
  • A laboratory study in Manitoba found in early reproductive stages, one lygus per inflorescence could reduce yield, primarily by causing pod abortion.
  • At later stages three lygus per inflorescence was required to affect yield. However, a concurrent field survey of fields with lygus bugs in Manitoba from 2008 to 2010 showed little economic effect of lygus bugs feeding on dry beans.

LIFE CYCLE
  • Overwinter as adults under plant debris adjacent to fields. Adults migrate into crops in spring and summer to lay eggs on stems. Adults are strong fliers.
  • Two generations per year in the southern prairies but only one in the northern areas.

CONTROL
  • Use a standard 40 cm (15 in.) diameter sweep net to sample crops to determine the need for control actions.
  • Monitor pulse crops for lygus bugs during flowering to pod development, until seeds in the pod become firm. Make 10 to 25, 180° sweeps at five to 10 representative locations in the field during the warm, sunny part of the day when lygus are most active (temperatures greater than 15°C).
  • Sample a minimum of two field edges and at each location, walk an arch that includes four to five sweep locations approximately 25 metres apart. For faba beans, 25 sweeps are recommended due to the low number of lygus required to do damage in the crop.
  • Count both adults and later instar nymphs. If the nymphs have the five black dots on their backs, include them in the count. Small nymphs that do not have wing pads are not expected to damage the crop and are not counted when estimating thresholds, providing the crop is monitored at early pod stage for faba beans.
  • If crop growth is too heavy, samples can be taken near the field edges or at right angles from the edges, as long as the crop is at a similar stage as the main part of the field. Samples should not be taken from poor areas with thin stands because lygus are far more abundant in these areas compared to thick stands, and field populations will be overestimated.

ECONOMIC THRESHOLD
  • None established.

RESOURCE

Seedcorn Maggot

Seedcorn Maggot, University of Kentucky

Seedcorn Maggot Adult, Photo Credit: Pest and Disease Library, Bugwood.org use

Damage
  • The adult seedcorn maggot looks similar to a common housefly and will emerge from eggs in the soil in late May. They are 6 mm long, grey flies, wings overlap when at rest. Larvae is white, tough skinned, and 8 mm long.
  • They will burrow into both the seed and the stem of developing dry bean plants, resulting in thinned stands and wilted plants.
  • Damage is worse when germination and emergence is delayed, so ensuring planting as early as possible into a warm, shallow seedbed encourages fast emergence and will help limit damage.

LIFE CYCLE
  • The seedcorn maggot overwinters as reddish brown pupae in the soil of harvested host crops.
  • The adult lays eggs in moist cracks in the soil that hatch after two to four days when temperatures are 10°C.
  • Females lay an average of 250–300 eggs in batches of 25–30 in freshly-tilled soils high in moisture and organic matter. Will also lay eggs on hosts infested with other root maggots.
  • Usually one generation but two overlapping generations are possible during warmer or extended summers.

CONTROL
  • Scout for the presence of all adult root maggots starting in mid to late May using yellow sticky cards or sweep nets.
  • Sprays are not effective and seed treatments are the only control registered to protect against the seedcorn maggot.
  • Seed treatments are registered for beans, peas, soybeans, and corn.  
  • Several species of predators and parasitoids attack all root maggot life stages and provide the greatest protection against root maggot depredation. Ground beetles and rove beetles feed on eggs, larvae and puparia; nematodes attack the larvae. Some fungal and bacterial pathogens also provide some control.
  • Rotate host crop with non-host crop. Increasing the seeding rate can decrease root maggot damage. Spring and/or fall tillage may reduce fly emergence by exposing puparia to predation. Depending on the crop, severely damaged crops could be ploughed under and immediately reseeded.

ECONOMIC THRESHOLD
  • None established.

REFERENCE

Wireworm

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 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.
  • 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 peas and there is no in-crop insecticide available to control wireworm.

REFERENCE

 

Special thanks to Saskatchewan Pulse Growers and Manitoba Pulse and Soybean Grower.