Insects and Pests of Field Crops: General Insects and Pests

 

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| Spring and Winter Canola | Other Crops | Soil Management |
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| Insects and Pests of Field Crops | Diseases of Field Crops | Appendices |

Pub 811: Agronomy Guide > Insects and Pests of Field Crops > General Insects and Pests

Order OMAFRA Publication 811: Agronomy Guide for Field Crops

 

Table of Contents

OMAFRA Publication 812, Field Crop Protection Guide, a companion publication to this publication, is the source for information on integrated pest management options and insect, pest and disease control products. Visit the OMAFRA website.


Soil Insects and Pests

Grubs

corn, soybeans, forages, winter cereals

Various types of grubs can attack field crops. European chafer is the most common problem grub in Ontario field crops, although June beetle and Japanese beetle grubs also cause damage. Proper identification of the species of grub present in each field is important, as their life cycles are different, which influences the management strategies implemented.

Description: Grubs are white and C-shaped, with an orange-brown head and dark posterior. Correctly identifying the species of grub requires using a hand lens focused on the anal bristles known as "rasters" that are positioned on the underside of the larva at the last abdominal segment of the larva (posterior). Each species has a particular "raster" pattern. Identifying the species will determine when feeding activity is expected and when control measures can be implemented.

Damage: Grubs feed on the fibrous roots 3-5 cm (1-2 in.) from the soil surface. Roots are pruned, causing plants to become stunted and eventually wilt. Intense root feeding results in poor emergence and plant death. Crops at risk from grubs include corn, soybeans, wheat and forages. Fields near areas of turf such as lawns, golf courses and pasture, are particularly prone to grub infestations. Crop damage is dependent on the timing of planting and crop emergence in relation to larval feeding activity. If the crop is planted after the grub species has completed its larval stages (feeding stage of the insect), crop damage can be avoided. Additional damage can occur from predators such as skunks and raccoons that dig up and feed on the grubs, although the damage is seldom economical.

Figure 13-1, Life Cycles and Feeding Periods for Common Grubs (European Chafer, June Beetle, Japanese Beetle), shows the differences and similarities in their life cycles.

European Chafer (Rhizotrogus majalis)

corn, forages, cereals

Description: European chafer larvae can be distinguished from other white grubs by their Y-shaped raster pattern, Plate 59. The adult is a medium-sized, approximately 14 mm (1/2 in.), light-brown, oval, scarab beetle, closely resembling the native June beetle. Chafers are also known as the annual white grub.

Plate 59. European chafer larvae are white with an orange-brown head and dark posterior. They are distinguished from other white grubs by the Y-pattern of the anal bristles (rasters).

Plate 59.European chafer larvae are white with an orange-brown head and dark posterior. They are distinguished from other white grubs by the Y-pattern of the anal bristles (rasters).

Life History: The European chafer is an annual grub, having only one generation per year. Chafers over-winter as larvae or "grubs" in the soil below the frost line. In April, these larvae migrate upwards, close to the soil surface and feed on plant roots. European chafer is more cold tolerant than the other grub species and can feed as soon as the soil thaws, even before the snow melts. Larvae stop feeding by mid-May, then pupate from mid-May to mid-June. Adult beetles emerge from the soil in early June to early July to mate. Adult chafers congregate in conspicuous mating flights and can be seen swarming at dusk. The adult females then locate cool, moist soil in nearby fields or lawns to lay their eggs. Eggs hatch and newly hatched larvae begin feeding on roots in early August until the ground freezes. The grubs then migrate below the frost line to overwinter.

Damage: Spring feeding damage by chafer larvae starts in April and is completed by mid- to late May. Corn and forages are at the most risk, while soybeans tend to miss feeding activity when planted after mid-May. Fall feeding damage by chafer larvae is most evident in the winter wheat crop. Adults do very little to no feeding.

Scouting Technique: It is best to scout for chafers in the fall in standing soybean stubble fields. Scout for grubs on the sandier knolls of fields and in areas where past injury was evident. Using a shovel, dig up approximately 30 cm2 (1 ft2) of soil, roughly 7.5-10 cm (3-4 in.) deep, in at least five areas of the field. Sift through the soil by hand, breaking up any clumps and count how many grubs are found in each sample.

Figure 13-1. Life Cycles and Feeding Periods for Common Grubs (European Chafer, June Beetle, Japanese Beetle)

Damaging stages are shaded.

Figure 13-1. Life Cycles and Feeding Periods for Common Grubs (European Chafer, June Beetle, Japanese Beetle)

 

Text Explanation for Figure 13-1. Life Cycles and Feeding periods for Common Grubs

 

Action Threshold for Corn and Cereals: The presence of two or more larvae per square foot (30 cm2) indicates the need for control.

Action Threshold for Forages: No thresholds are available, but two or more larvae per square foot (30 cm2) indicates that control may be necessary, particularly in a first-year crop.

Management Strategies for All Crops:

  • Cultural options include disturbing the soil by tillage or disking, which brings the grubs to the surface where they are exposed to the elements and natural enemies such as birds, skunks, raccoons, etc. For this strategy to be effective, plow in the fall before the grubs migrate below the plow depth.
  • No rescue treatments are available.

Management Strategies for Corn and Cereals:

  • Use an insecticide seed treatment that is registered for European chafer.
  • If grub populations are high (i.e., four or more grubs per square foot), use the higher rate of an insecticide seed treatment.
  • Avoid planting corn if the chafer population is extreme; plant soybeans instead.
  • Plant crop into ideal soil conditions so that the crop will rapidly become established and able to tolerate low to moderate grub feeding.

Management Strategies for Forages:

  • Avoid planting alfalfa if chafer populations are high. Plant other crops that have insecticide seed treatments available to reduce grub populations.
  • A well-managed pasture with a good mix of legume and grass species may help reduce stand loss, as grubs tend to feed more on the grass species. Over-seeding or reseeding may be required for a few years to compensate for what the grubs have taken out.

June Beetle (Phyllophaga spp.)

soybeans, forages

Description: June beetle larvae can be distinguished from other white grubs by their oval-shaped raster pattern, where two rows of rasters run parallel to each other Plate 60. The adult is slightly larger, roughly 20 mm (3/4 in.), than European chafer and is reddish-brown to black in colour. The June beetle is also known as the true white grub or June bug.

Plate 60. June beetle larvae have a raster shaped like an oval, with the two rows of rasters running parallel to each other.

Plate 60.June beetle larvae have a raster shaped like an oval, with the two rows of rasters running parallel to each other.

Life History: June beetles have a 3-year life cycle. Adults emerge from the soil mid-May to mid-June and lay eggs. Adults tend to congregate at dusk in large masses on trees and shrubs to mate. Eggs are laid in moist soil and hatch within a few weeks. First instar larvae begin feeding on plant roots and molt into the second instar before migrating deep into the soil to over-winter. Once the soil warms up the following spring (Year Two), the second instars begin feeding and will remain as larvae throughout the year, molting once into the third instar. The second year of their life cycle is therefore the most destructive. Larvae again prepare to over-winter by migrating deeper in the soil once temperatures drop, until the following spring. In Year Three, the third instar larvae feed on roots for a short time before pupating and becoming adults. These adults will remain dormant in the soil for the rest of the season and only emerge the following spring.

Damage: Damage depends on which year of the life cycle the majority of the larvae are in. The second year of the life cycle is the most damaging, because there is a full growing season of the larval stage. Soybeans and forages tend to experience the most injury from this insect, especially when the crop is still young. Adults can feed on tree species and ornamental plants such as roses but do not feed on field crops.

Scouting Techniques: Scout for grubs on the sandier knolls of the field and in the areas where injury was evident in previous years. Using a shovel, dig up approximately 1 square foot of soil, (30 cm2) about 7-10 cm (3-4 in.) deep, in at least five areas of the field. Sift through the soil by hand, breaking up any clumps and count how many grubs are in each sample.
Action Threshold: No thresholds are available for June beetle grubs, though two or more larvae indicate the need for control.

Management Strategies for All Crops:

  • Use insecticide seed treatments in fields with a history of damage, particularly if grubs appear to be mainly in the second year of their life cycle when the majority of the feeding will take place.
  • Avoid planting early in cool, wet springs.
  • Plant in ideal soil and weather conditions to help promote rapid germination and seedling growth.
  • No rescue treatments are available. Tillage can help kill some of the larvae and expose them to their predators such as birds, skunks and racoons.

Management Strategies for Forages:

  • Avoid planting forages in infested fields, particularly if grubs appear to be mainly in the second year of their life cycle, when the majority of the feeding will take place.
  • Plant fields with a history of crop loss due to grubs to another field crop that has an insecticide seed treatment available for grub control. Re-assess the grub population following this control tactic to determine if forages can be planted in that field again.
  • A well-managed pasture with a good mix of legume and grass species may help reduce stand loss, as grubs tend to feed more on the grass species. Over-seeding or reseeding may be required for a few years to compensate for what the grubs have taken out.

Japanese Beetle (Popillia japonica)

soybeans, forages

Description: Japanese beetle grubs can be distinguished from other grubs by the wide, shallow V-shaped raster pattern Plate 61.

Plate 61. Japanese beetle larvae can be distinguished from other grubs by the wide, shallow, V-shaped raster pattern.

Plate 61.Japanese beetle larvae can be distinguished from other grubs by the wide, shallow, V-shaped raster pattern.

The grubs are also much smaller in size than European chafer and June beetle grubs. The adult beetles are approximately 13 mm (1/2 in.) in length and can be easily identified by their bright, metallic-green head and coppery wings tinged with green edges Plate 62. They have 12 white tufts of hair along the boundary of their wings.

Plate 62. Japanese beetles have a bright, metallic green head with coppery wings tinged with green edges. Twelve white tufts of hair appear at the wing boundary.

Plate 62.Japanese beetles have a bright, metallic green head with coppery wings tinged with green edges. Twelve white tufts of hair appear at the wing boundary.

Life Cycle: Japanese beetles have only one generation a year. They over-winter as third instar larvae below the frost line. Once the soil has warmed up above 15°C, the larvae migrate to the surface and feed on plant roots until mid- to late June, after which time they pupate to become adults. Adults emerge in early July and live for approximately 40 days. Once mated, females lay their eggs in the soil, which hatch in a few weeks. Larvae begin feeding on roots, molting through three instars before preparing for over-wintering by migrating below the frost line by early October.

Damage: Both the larval and adult stages can feed on field crops. This pest is most commonly found in the Niagara/Hamilton region, though it is known to be present across Ontario. Soybean and hay fields in particular tend to experience some root-feeding damage from the larvae. Adults will also feed on soybeans, dry edible beans, fruit crops and ornamental plants, causing leaves to appear skeletonized.

Scouting Technique for Larvae (Grubs): Scout for grubs on the sandier knolls of the field and in the areas where past injury was evident. Using a shovel, dig up approximately 1 square foot of soil (30 cm2), about 7-10 cm (3-4 in.) deep, in at least five areas of the field.

Scouting Technique for Adults in Soybeans: Scout 20 plants in at least five areas and compare the damage found to Figure 13-2, Defoliation Chart for Soybean Leaf-Feeding Insects.

Action Threshold for Larvae (Grubs): No thresholds are available for Japanese beetle grubs, though two or more larvae indicate that control may be necessary.

Action Threshold for Adults in Soybeans: If the defoliation exceeds the thresholds in Table 13-3, Standard Damage Thresholds for Soybean Insect Defoliation, a rescue treatment may be warranted to prevent excessive yield loss.

Management Strategies for All Crops:

  • Use insecticide seed treatments in fields with a history of damage by the larvae.
  • Avoid planting early in cool, wet springs. Plant in ideal soil and weather conditions to help promote rapid germination and seedling growth.
  • No rescue treatments are available for grubs. Tillage can help kill some of the larvae and expose them to their predators such as birds, skunks and raccoons.
  • For further recommendations on adults, see Defoliating Insects.

Wireworm (Limonius spp. and others)

corn, soybeans, cereals, dry edible beans

Description: Wireworms are larvae that are 7-35 mm (1/4-1 1/3 in.) long, cylindrical, copper-brown-coloured and hardened Plate 63. Adult wireworms are beetles that have the ability to flip themselves upright when placed on their backs. As they flip there is an audible click, giving them their name "click beetles."

Plate 63. Wireworms have long, cylindrical, copper-brown, hardened bodies. They affect many crops, usually when following grassy crops in rotation.

Plate 63. Wireworms have long, cylindrical, copper-brown, hardened bodies. They affect many crops, usually when following grassy crops in rotation.

Life History: Wireworms take up to 6 years to develop from egg to adult, spending most of their life as larvae. They over-winter as larvae in the soil below the frost line. When soil temperatures warm in the spring, the larvae move to the surface to feed. Due to their long life cycle, the larvae can damage several successive crops, feeding on the roots of weeds, grasses and crop plants. Once soil temperatures become hot, and soil moisture decreases, the larvae migrate downward and may be difficult to find. As they become adults, the larvae migrate back to the surface, pupate and the adult emerges to mate and lay eggs in grasslands or weedy areas.

Damage: Wireworms are most active during the months of April to June and occur most often in fields that have little disturbance. The larvae attack roots, seeds and germinating seedlings of many crops such as corn, soybeans, spring cereals, dry edible beans and potatoes. Non-uniform growth or gaps in the stand may be due to wireworm feeding on germinating seeds. Injured seedlings appear stunted and wilted, with leaves sometimes becoming purple or blue at the tips. Wireworms are rarely a problem in fall-planted cereals, however, they can be serious in spring-planted grains. The problem is usually worse in the second year after sod, following years with high grassy-weed pressure or when corn and cereals are frequently in the rotation. They are also generally more prevalent in sandier soils, especially on the knolls.

Scouting Technique: The best time to scout is in mid-April, a few weeks before planting; if soil moisture and temperatures are adequate, fall sampling is also possible. Establish two bait stations per "high-action" site in each field. Dig a hole at each station, approximately 15 cm (6 in.) wide and 5-8 cm (2-3 in.) deep. Choose one or two high-action sites in the field (i.e., sandy knolls, heavy grass infestations). Bury a nylon mesh bag with 1 cup equal parts untreated and soaked corn and wheat or freshly cut potatoes at the bottom of the station. Mound the soil over the bait to prevent standing water. Securing a dark piece of plastic over the mound will help warm the bait station, increasing the fermentation of the bait, which will be more attractive to the wireworms. Place a flag at the bait station to make it easier to find again. Return to the stations a few days before planting to sift through the bag contents and record the number of larvae found per station.

Action Threshold: One wireworm per bait station.

Management Strategies for All Crops:

  • Use insecticide seed treatments or in-furrow or banded soil insecticides in fields that have reached threshold, have a history of wireworm incidence or are following grassy sods.
  • No rescue treatments are available. However, controlling grassy weeds in crops previous to corn will help with prevention.

Millipedes(various species)

corn, soybeans

Description: Millipedes are not insects but arthropods. They are hard-shelled, cylindrical and approximately 2.5-5 cm (1-2 in.) long. They get their name (milli: thousands, pedes: legs) from having many legs - two short pairs of legs per body segment in the adult stage. Adult millipedes are dark reddish-brown to grey-black in colour and have hardened bodies, while the immature millipedes are white, have fewer legs and do not have hardened bodies. As they mature, they develop more legs and turn darker in colour. Another distinguishing characteristic is that they coil up tight when disturbed.


Do not confuse millipedes with wireworms; wireworms are coppery-brown in colour and only have six legs.


Life History: Both adult and immature millipedes over-winter in the soil under debris, rocks, etc. They can live for several years in the soil, taking up to 5 years to mature to the adult stage. They have become more prevalent with the adoption of reduced or no-till systems because of the increase in surface residues.

Damage: Millipedes are typically beneficial. They help decompose organic matter and feed on other insects. However, when planting too early in cool, wet springs, conditions are ideal for millipedes to feed on the seeds and young seedling roots, particularly corn and soybeans. No-till fields with higher residue soils and lots of organic matter are at higher risk, though damage has also been experienced in conventional fields. Deep planting can also promote injury. Droughty conditions will lessen their impact.

Scouting Technique: There are currently no established scouting methods for millipedes. Inspect roots, germinating seed and soil around areas with gaps in the plant stand. Millipedes could still be present on the roots or within the seed. If early-season injury is noticeable but no pest is present, setting up wireworm bait stations consisting of entirely soaked corn seed near the gaps in the stands will also be effective at capturing millipedes to determine their presence and eagerness to feed on corn seed.

Action Threshold:No threshold is available at this time.

Management Strategies for Corn and Soybeans:

  • Insecticide seed treatments have not been found to be effective at controlling millipedes. No rescue treatments are currently available.
  • Plant in ideal conditions to improve seed germination in these fields, particularly when cool wet springs are forecasted.

Seedcorn Maggot (Delia platura)

corn, dry edible beans, soybeans

Description: The seedcorn maggot is a small, yellowish-white, headless, legless larva Plate 64. The body tapers to the front with two small mouth hooks protracting. The maggots burrow into germinating seeds and the below-ground parts of emerging seedlings, producing weak seedlings. The adults resemble a small housefly that is slender, light grey and approximately 5 mm (1/5 in.) in length.

Plate 64. Seedcorn maggots are small, headless, legless larvae that burrow into germinating seeds and weaken the seedling.

Plate 64.Seedcorn maggots are small, headless, legless larvae that burrow into germinating seeds and weaken the seedling.

Life History: The seedcorn maggot over-winters in the pupal stage. Adults emerge in early spring. Once mated, female adults (flies) search for an egg-laying site from April until the middle of June. The females are attracted to moist soils that give off an odour of decaying organic matter, such as crop residues, areas where manure has been applied or freshly tilled soil. Weeds are also attractive to females. The adults lay their eggs in the soil. The larvae then develop in the soil and organic residue, feeding on germinating seeds.

Damage: Seedcorn maggot is usually a problem during cool, wet springs when germination is delayed. The maggots feed on the swollen, ungerminated seed. They can be found in the cotyledon, embryo and hypocotyl. They can also mine the stem of the young seedling. Slow emergence and/or reduced stand establishment can occur. Damaged seedlings that germinate often die or lag behind.

Scouting Technique: Unlike wireworm, seedcorn maggot damage is usually found over a generalized, large portion of the field. Nothing can be done to rescue a damaged field except replanting if necessary. High-risk factors include freshly tilled soil with heavy crop residue, recently applied manure, recently tilled green manure, deep planting and early planting followed by cool, wet spring conditions. Look for signs of poor stand emergence and feeding damage at the base of the newly emerging plants.

Action Threshold: No threshold is available at this time.

Management Strategies:

  • Consider insecticide seed treatments or in-furrow, soil-applied insecticides in early-planted fields where large amounts of manure or residue have been recently incorporated.
  • Use good-quality seed that will emerge quickly.
  • Plant in good soil conditions when cool wet weather is not in the forecast to ensure rapid seedling emergence.
  • There are no rescue treatments available. Use an insecticide seed treatment or in-furrow insecticide in fields requiring replanting.

Slugs (Deroceras reticulatum)

corn, soybeans, newly seeded forages, canola

Description: Juvenile and adult slugs are soft-bodied, legless, greyish or mottled in appearance and have a slimy or gelatinous covering that protects them from drying out. They are essentially snails without a shell. The head has two pairs of tentacles. Slugs usually range from 1-3 cm (1/3 in.) in length but can reach up to 10 cm (4 in.).

Life History: There is one generation per year but two populations, one maturing as adults in spring and one maturing as adults in fall. Therefore, damage can occur both in the spring and the fall on young developing plants. Both eggs and adults over-winter. Juvenile slugs hatch from eggs in the spring and the fall and are the most damaging stage of the pest. Slugs are most active during cool and wet periods in spring and fall and prefer environments with high humidity and relatively cool temperatures. Debris, such as crop litter or manure, provides them with shelter from the sun.

Damage: Slugs feed above or below ground, depending on the moisture level. They can feed on germinating seeds and seedlings, with no real preference for a plant part Plate 65.

Plate 65. Slugs are soft-bodied, legless and greyish or mottled. They have a gelatinous (slimy) covering that leaves trails where they have travelled.

Plate 65. Slugs are soft-bodied, legless and greyish or mottled. They have a gelatinous (slimy) covering that leaves trails where they have travelled.

Slugs feed on lower parts of larger plants, partly or completely eating through leaves, resulting in ragged holes that cause a skeletonized appearance on leaves Plate 66.

Plate 66. Foliar damage caused by slugs. Slugs feed on all parts of the plant, leaving ragged holes. Feeding on the growing point can kill the plant.

Plate 66.Foliar damage caused by slugs. Slugs feed on all parts of the plant, leaving ragged holes. Feeding on the growing point can kill the plant.

Feeding can resemble hail damage, and severe defoliation can result. If slug populations are high, they may feed on germinating seeds, hollowing them out before they can emerge. Higher-risk fields include no-till corn, soybeans and canola, especially fields with considerable crop residue, wheat fields underseeded with red clover, newly seeded alfalfa and fields following forages, especially grasses. Knowing the slug population of each field in the fall will indicate how significant the problem will be the next spring. It is the same population that over-winters and feeds in the spring.

Scouting Technique: Scout for slugs at night or in the early morning hours, when they are active (nocturnal). Look for gaps in the stand, stripping of leaf tissue and/or small holes chewed in the leaves. Check under debris and clumps of soil. A certain sign of slugs is a slimy, silver-coloured trail on the plants or soil. To determine population levels, take small pieces of plywood, approximately 0.6-0.9 m (2-3 ft) long, or roofing shingles and position them on the soil surface in fields that have been harvested. Use 10-15 boards randomly scattered across the field to provide a good indication of population levels. These boards will act as shelters for the slugs. Visit the boards every 5 days for approximately 1 month, counting the number of slugs present under the boards. Morning is the best time to look, since slugs will still be in their shelters.

Action Threshold: No action thresholds are available. If slugs are commonly found under monitored boards as described above, the field should be considered at high risk for slug injury in the spring. Scout these fields again in the spring to confirm risk. Young seedlings and germinating seeds are most impacted.

Management Strategies:

  • Planting into conditions that help the crop grow quickly can avoid heavy slug damage.
  • Tillage can be used against slugs since the elimination of the crop cover exposes the slugs to dehydration and predation by birds and mammals. Zone tillage or row sweepers can help speed up the drying of the row area, thus deterring slug feeding. Moving trash away from seedlings may help reduce damage.
  • There are presently no economically feasible chemical methods available for slug control in field crops. Slug baits are available for field crops but are very expensive and are only recommended for use in small problem areas of the field. Apply baits shortly after May 24 to achieve the highest potential for success.
  • Experiments with 28% nitrogen/water mixtures or foliar potash applications have proven to be inconsistent and are not encouraged.

     


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca
Author: OMAFRA Staff
Creation Date: 30 April 2009
Last Reviewed: 30 April 2009