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Corn Pest Forecasting

Insect pests are one of the important limiting factors for corn production in Ontario as well other corn-growing areas of Canada and United States. Several species of insect occur annually in Ontario corn growing areas and cause significant economic damages on corn. Some of them also transmit bacterial or viral diseases on corn. Few species of corn pest, such as western bean cutworm, recently emerged in Ontario, and became wide spread and problematic. Several corn pests also infest other field crops and vegetables.

Most of corn pests can overwinter in Ontario. The life cycle of these pests are influenced by temperature. Therefore, accumulated growing degree day are useful to predict the emergence of these pests in the main corn growing seasons. Weather based scouting advisories are available for six economically important insect pests of corn: (i) Western bean cutworm, (ii) European corn borer, (iii) Corn earworm, (iv) Corn rootworm, (v) Japanese beetles and (vi) Seed corn maggots.

Click the insects name below for more information and how it affects the corn.

Western Bean Cutworm

Western bean cutworm (WBC) is an economically important pest of corn, edible beans and vegetables. The pest was first reported in Ontario in 2008. The pest is also problematic in many states of USA including Wisconson, Nebrasaka, Arkansas and Colorado since 2000. WBC feed in corn ears, grains or bean pods. Multiple larvae can feed on a single ear causing significant damage on corn.

Key Diagnostic Features:

Larvae: Larve has distinguishing marking, i.e. dark brown shield-like structure just behind the head two broad dark brown.

Adult: Both wings of moth have white band running along the margin of wing and has a spot or moon and boomerang-like mark.


European Corn Borer

Two types of strains, univolting (one generation per year) and bivoltine (multiple generations per year) are present in Ontario. In South of a line from Sarnia to Simcoe, bivoltine strain occurs. In North of this line, a univoltine strain occurs. The borer over-winters as larvae in corn stalks and when temperature exceed 10°C, the larvae pupated and developed to adult to continue lifecycle in corn. The larvae of European corn borer feed on stalk and make a tunnel in the stalk. Tunneling of stalk would cause stalk breakage and dropped ears. Insect damage also increases the stalk rot problems and physiological stress on plants.

Key Diagnostic Features:

Larvae: cream to pink with black heads and two black spots per abdominal segment.

Adult: Adult are straw-colored with dark wavy lines running across each forewing.


Corn Ear Worm

Corn ear worm is also an economically important pest. The larvae feed mainly on silk and developing kernels. The pest does not overwinter in Ontario and migrate from southern US.

Key Diagnostic Features:

The size and presence of the stripes differentiate earworm from European corn borer, while its tan head colour differentiates it from fall armyworm.


Corn Root Worm

There are two species of corn rootworm in Ontario; northern corn rootworm (Diabrotica barberi) and western corn rootworm (D. virgifera virgifera). Both species causes damage to corn root and widely distributed and considered as an economically important pest in corn belts of Canada and USA. Both larvae and adults are damaging to corn root. Heavy infestation cause lodging problem in corn. Adults can also feed on soybean but damages are not reported as economical. These root worms are adapted in soybean-corn rotation system.

Key Diagnostic Features

Northern corn rootworm beetles are tan or light to dark green color with no marks in their wings. Western corn rootworm adults are yellow to green with three wavy black stripes on their back.


Japanese Beetles

Japanese beetles (Popillia japonica) infest field crops including corn, soybean, and dry beans in Ontario and other provinces of Canada. The pest is more problematic in the Niagara/ Hamilton regions. The beetle is also problematic in several soybean and corn growing states of USA. The adults feed and destroy both foliage and pod of soybean. In addition, this pest also infests about 250 host including several tree fruits and berries.

Japanese beetles have only one generation in a year. Both larvae and adults cause damage to corn and soybean. Larvae feed on roots. The beetles overwinter in Ontario. Once the temperature rises above 15°C, the activities of larvae will begin and feed root of field crops. The adults emerge on mid-summer and cause damage on soybean foliage and pod. It also clips the silk of corn.

Key Diagnostic Features

Larvae: The beetle grubs have wide, shallow V-shaped raster pattern in abdominal segment.

Adults: Adult beetles have bright metallic-green head and coppery wings with green edges.

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Seed Corn Maggots

Seed corn maggots (Delia platura) attack soybean, seed corn other crops. The maggots damage the root soybean and corn at seedling stage, which cause poor emergence or poor seedling health. The pest also damages the embryo of seed and cause germination failure.

SCM overwinters as a pupa in the soil. Adult flies emerge in spring after the ground has thawed and sufficient heat units, or degree-days, have accumulated for SCM to reach the adult stage. Eggs hatch within 2 to 4 days and larvae feed belowground on seeds and germinating seedlings. Adults emerge in early spring. Once mated, female adults (flies) search for an egg-laying site from April until the middle of June. There are three generations per year. Seedcorn maggot is usually a problem during cool, wet springs when germination is delayed. The maggots feed on the swollen, ungerminated seed.


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