Insects and Pests of Field Crops: Cereal Insects and Pests

| Corn | Soybeans | Forages | Cereals | Dry Edible Beans |
| Spring and Winter Canola | Other Crops | Soil Management |
| Soil Fertility and Nutrient Use | Field Scouting |
| On-Farm Stored Grain Management | Weed Control |
| Insects and Pests of Field Crops | Diseases of Field Crops | Appendices |

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

Excerpt from Agronomy Guide for Field Crops
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Table of Contents

• Introduction
  • Table 13-6. Cereal Insect Symptoms in the Field
• Cereal Aphid Complex
  • Bird Cherry-Oat Aphid
  • English Grain Aphid
  • Corn Leaf Aphid
• Hessian Fly
• Cereal Leaf Beetle
• True Armyworm
• Fall Armyworm

Introduction

Table 13-6, Cereal Insect Symptoms in the Field, shows insects and pests that may be causing symptoms in the field.

This section describes insects and pests that affect only cereal crops. The insects and pests listed below affect cereals as well as other crops.

European chafer
Fall armyworm
June beetle
Slugs
Wireworm

Cereal Aphid Complex:

Bird Cherry-Oat Aphid (Rhopalosiphum padi)

English Grain Aphid (Sitobion avenae)

Corn Leaf Aphid (Rhopalosiphum maidis)

Description:

The bird cherry-oat aphid is the most common aphid found in Ontario cereals. These aphids are small, 2 mm (1/12 in.) or less. Adults are olive-green with patches of red-purple near the rear of the abdomen, between a pair of tubes called cornicles Plate 96. The cornicles and legs are pale green; the antennae are long and black. Younger aphids are light green.

Plate 96. Bird cherry-oat aphids are dull, olive-green with patches of red-orange near the rear of the abdomen.

The English grain aphid is typically the largest of the three species and is pale green or light orange with long legs that may appear green to black. They have long black antennae and cornicles.

The corn leaf aphid is also olive green, but the legs, cornicles and antennae are black and the shape of the body is more rectangular, while the bird cherry-oat aphid is bulb-shaped. Similar to all aphids, these species are soft-bodied, winged or wingless, with piercing and sucking mouthparts that suck the juices (nutrients) from young plant tissues. Aphids secrete a sticky substance referred to as "honeydew," which can cause sooty mould.

Life History:

Cereal aphids have over-wintered in Ontario, particularly in mild winters with prolonged snow cover. Fields planted in late summer or early fall (August/September) are at highest risk of fall infestations.

Damage:

Seldom a direct problem in Ontario. On young plants, aphids cluster on the upper sides of leaves near the base of the plant. Eventually, aphids will climb to the top and can be found in the leaf whorls. High populations can result in fields appearing to have large bronze patches. Cereal aphids are vectors of barley yellow dwarf virus (BYDV). See Barley Yellow Dwarf Virus.

Scouting Technique:

Fall scouting for cereal aphids is important, as early-season infection with BYDV is most harmful to cereals. In spring, scout the field weekly prior to heading. Examine 20 stems in five areas across the field. Shake the plants over a piece of paper and count the number of aphids present or look for colonies specifically at the leaf collar. Also make note of any predators present and whether the aphids are parasitized or infected with a fungus.

Action Thresholds:

Prior to the heading stage, 12-15 cereal aphids per stem, and up to 50 aphids per head once headed.

Management Strategies:

• Apply insecticide when the action threshold has been reached. To prevent barley yellow dwarf virus in winter cereals, avoid planting any earlier than 10 days prior to optimum planting date as shown in Figure 4-4, Optimum Date to Seed Winter Wheat Across Ontario.
• Controlling volunteer wheat 2-3 weeks before planting may help reduce aphid populations in the vicinity of cereal crops.
• Several natural enemies feed on aphids, including lady beetle adults and larvae, syrphid fly larvae and lacewing larvae. Parasitic wasps are also a key natural enemy that can take down aphid populations before treatment is necessary.

Hessian Fly (Mayetiola destructor)

Description:

Adult Hessian flies resemble small mosquitoes. They are smoky grey and fragile, and have pointed abdomens that are a dull red. Adults are weak flyers and only live about 3 days. Larvae are 2 mm (1/12 in.), legless, white maggots. Pupae are reddish-brown, shaped like flax seed and can be found at the base of the plant in late fall and early spring.

Life History:

Two generations occur per year. The Hessian fly over-winters as "flax seed" puparia in the base of old plant crowns. Adults emerge in the spring. Rain triggers adult emergence. Females lay their long, reddish eggs in rows like sausage links, on the upper surface of leaves of young winter wheat or volunteer wheat. Larvae develop and feed for approximately 3 weeks before forming a puparium in mid-June. A second generation emerges, and the insect continues its cycle until late September when it forms a puparium for over-wintering.

Damage:

Damage can occur in both spring and fall, though it is the fall population that is the main concern, particularly for the winter wheat crop. Other grain crops including barley, oat and rye are considered more tolerant, though infestations may still occur.

Fall injury:

Fall plantings may stunt and turn dark-green. Larvae on young plants feed between the leaf sheath at the base of the plant. The enzymes they secrete into the plant cause the stems of the plant to thicken, the plant to stunt and the leaves to broaden. Multiple tillers can develop. Infested plants take on a dark bluish-green appearance. Winter survival of the crop can be impacted.

Spring injury:

Spring damage by the first population is concentrated at just above the nodes where the larvae feed. Internodes become shortened, impacting nutrient transport to the head. Stems, when pulled, break easily at infested nodes. Heads can turn white and plants can lodge. High risk fields include susceptible varieties of winter wheat that are planted early, when adults are still flying.

Scouting Technique:

In the spring, scout fields when heads begin to fill. Look for plants that have shortened internodes and white heads. Gently tug at the stem of the plant to see if it breaks easily at the node. Look for larvae within the internode where the stem broke off. In the fall, begin scouting 3 weeks after wheat plants have emerged. Examine 20 plants in five locations across the field. Pull away leaves to view the base of the leaf at the stem. Look for the "flax seed" puparia to determine the percentage of infestation.

Action Threshold:

None available. Control is based on prevention.

Management Strategies:

• Prevention is the key form of control.
• Delay planting of winter cereals until after the fly-free date will ensure that plants have not emerged until after Hessian adult flies are no longer flying and laying eggs. Fields planted in August/early September are most at risk. See Planting Dates, for optimum seeding dates for your region.
• Do not plant wheat 2 years in a row in the same field. Destroy volunteer wheat and stubble before planting.
• Resistant varieties are available. No rescue treatments are available.
  

Cereal Leaf Beetle (Oulema melanopus)

Description:

The cereal leaf beetle (CLB) adult is a metallic, blue-green beetle, approximately 5 mm (1/5 in.) in length, with a reddish-orange head and legs Plate 98.

Plate 98. Cereal leaf beetle adult is metallic, blue-green with a reddish-orange head and legs.

The larvae are 6 mm (1/4 in.) in length when mature and yellowish in colour, but this colour is obscured by a black deposit of fecal material making it slug-like in appearance Plate 97.

Plate 97. Cereal leaf beetle larvae are yellowish, but this colour is obscured by a black deposit of fecal material, making them slug-like in appearance.

Life History:

CLBs over-winter as adults in leaf litter in sheltered areas such as woodlots and heavy crop debris. These adults emerge in early spring. The mated females then lay their eggs in wheat fields on the upper surface of leaves. The eggs hatch, and larvae are present by mid-May. The larvae will pupate, and adults will emerge by mid-June. Adults feed on wheat briefly and then congregate in corn fields, feeding for a short period before going dormant until fall. In the fall, adults become active again and make their way to their over-wintering sites. There is one generation per year.

Damage:

Cereal leaf beetles feed on wheat, oat, corn, forages and grassy weeds. Spring plantings are most attractive, particularly late plantings, though some winter wheat can also be infested in the spring. Both adults and larvae cause damage by chewing long strips of tissue between the leaf veins, leaving the top layer of the leaf intact. This creates a window-paning or "skeletonizing" effect. Most of the injury is caused by the larvae in June. Heavily damaged fields appear silver.

Scouting Technique:

Begin scouting in late April. Examine 20 plants in five locations across the field. It is important to scout various areas of the field, as CLB tends to be unevenly distributed across the field. Record the number of beetles and larvae found per plant. Scout every 5 days, as damage can increase dramatically within days.

Action Threshold:

One CLB adult or larvae per stem warrants control, especially in the earlier stages of the crop (before heading).

Management Strategies:

• Natural enemies are highly effective at controlling this pest. For the safety of these natural enemies, chemical control is not recommended unless pest population exceeds the action threshold.
• Clean plowing increases the risk of this pest, because the over-wintering sites of the parasites are destroyed.

True Armyworm (Pseudaletia unipuncta)

corn, forages, cereals

Description:

True armyworms (also known as common armyworm), when full grown, are 4 cm (1 1/2 in.) long. The dull-green to brown larvae can easily be confused with other caterpillars, including variegated cutworm and fall armyworm. Two distinguishing features of true armyworm are white-bordered stripes running laterally along the body and dark diagonal bands at the top of each abdominal proleg Plate 69. The head is yellow-brown with a network of dark-brown lines creating a mottled pattern. The adult sand-coloured moth has distinctive white spots on the centre of each forewing.

Plate 69. True armyworm larvae have black bands at the top of each proleg and a yellow-brown head with dark brown veins in a striped pattern.

Life History:

True armyworms over-winter as partially grown larvae. In early spring, the moths emerge and prefer to lay their eggs in grassy vegetation, including cereals, grassy forages and rye cover crop. Larvae hatch from the eggs and feed at night or on overcast days for approximately a month. There are two generations per year, but it is the first generation that tends to do the most damage to corn in Ontario. Outbreak years tend to coincide with cool wet springs that are detrimental to the parasites that typically control armyworm.

Damage:

True armyworm larvae feed at night. Most feeding damage is done on cereals during July. True armyworms do not feed on pure stands of alfalfa but will feed on alfalfa/grass mixtures. In conventional-till corn fields, damage usually occurs first in the border rows, whereas infestations may develop throughout no-till corn following small grains or grass. True armyworm also frequently invades corn fields from neighbouring cereal fields. Larvae strip the leaf margins, moving up the plant to feed on the panicles and flowers leaving only the midrib. As long as the growing point of the plant is not damaged, the corn plant will be able to recover from moderate feeding.

Scouting Technique:

The best time to scout for true armyworm is at or shortly after dusk. Examine 20 plants in five areas in the field (100 plants total). During the day, you may find the larvae in the whorl, leaf axil, amongst the crop debris on the soil surface or under soil clods. Also, you may find brown frass, often mistaken for eggs, in the whorl or on the soil near the plant. When scouting, check the backs of armyworms for eggs. These small, oval, yellowish eggs are usually located just behind the head of the larva. These are eggs of a parasitic fly. The eggs will hatch, and the maggots will kill the armyworm larvae. Record the size and number of larvae. Scout along the field boundaries bordering cereal and corn crops as larvae will "march" in from neighbouring fields and may be controlled prior to entering the corn field.

Action Threshold for Corn, Cereals:

For corn past the 6-leaf stage, and cereals at any stage; if 50% of the plants are showing damage and are infested with larvae smaller than 2.5 cm (1 in.), insecticide treatment may be warranted.

As long as the growing point of the plant is not damaged, the corn plant is usually able to recover from moderate feeding. With early-season feeding, insecticide may be warranted in seedling corn if there are two or more unparasitized larvae per seedling and feeding damage exceeds 10%.

Action Threshold for Forages:

Control is warranted when five or more larvae (smaller than 2.5 cm) per square foot are found. Avoid treating with insecticides when large numbers of parasitized larvae are present. In seedling crops, two to three larvae (smaller than 2.5 cm) per square foot may warrant control.

Management Strategies:

• If the larvae are over 2.5 cm (1 in.) long, there is no benefit in applying insecticide, since most of the feeding damage has already occurred.
• Treatment may be confined to infested areas. If armyworm are migrating from adjacent cereal or corn fields, spraying an insecticide along the field border may be sufficient.
• Parasites and other beneficial organisms usually keep armyworms from reaching damaging levels, though cool, wet springs are not favourable for these parasites. Avoid treating with insecticides when large numbers of parasitized larvae are present.
• Because grassy, weed-infested corn is attractive to armyworm moths for egg-laying, eliminate weeds from the corn crop and field borders. However, late-season grass control may not be a good option, since this will cause the feeding larvae to migrate from the grassy weeds that are now dead to the crop itself.

Fall Armyworm (Spodoptera frugiperda)

Fall armyworm is an important pest of forages.