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Ministry of Agriculture, Food and Rural Affairs

Corn Leaf Aphids

Aphids on corn husk Aphid feeding injury – poor kernel fill Corn leaf aphidsClick to enlarge.

Beginner

Scientific Name
Rhopalosiphum maidis

Identification

  • The corn leaf aphid is the most common aphid found in corn
  • It is blue-green in colour and less than 2mm (1/12 in.) in length
  • It has a pear-shaped body with two cornicles at the tip of the abdomen
  • The corn leaf aphid feeds on the tassels, cobs and upper leaves of corn plants

Often Confused With
Thrips

Period of Activity
Aphids are present throughout most of the growing season.  Populations build quickly during hot, dry weather.

Scouting Notes
Examine 10 sets of 10 plants per field.  Look for developing colonies on the ears and tassels.  A plant with more than 20 aphids is considered infested.  Take note of weather population levels are increasing from week to week.

Thresholds

10% of ears infested (ears with more than 20 aphids are considered infested).

Advanced

Scientific Name
Rhopalosiphum maidis

Identification
The corn leaf aphid is the most common aphid found in corn.  It is blue-green in colour and less than 2 mm (1/12 in.) in length.  It has a pear-shaped body with two cornicles at the tip of the abdomen.

Corn leaf aphids have piercing, sucking mouthparts.  They feed on the tassels, cobs and upper leaves of corn plants.  Aphids rarely cause actual yield losses in sweet corn; however their presence on the husk often results in an unmarketable ear.  Extremely high populations during pollen shed and silking may result in reduced pollination or poor kernel fill, especially if the silks and tassels become covered with honeydew and sooty mould as a result of the feeding.

Virus transmission is not usually a problem in sweet corn.

Often Confused With
Thrips

Biology
Corn leaf aphids do not overwinter in Canada.  They migrate northwards on wind currents throughout the summer.  Populations tend to increase over the course of the growing season, and are often highest during hot, dry periods.  Female aphids are able to reproduce without mating, giving live birth to wingless nymphs.  There are several generations per year.

There is a large difference in the attractiveness of different sweet corn varieties to corn leaf aphids.  In general Sh2 cultivars (supersweet) are likely to experience more damage than Su (normal) or Se (sugar enhanced) cultivars.

Aphids are attacked by several types of predators and parasites and these can have a significant impact on aphid populations.  Predators include ladybird beetle adults and larvae, lacewing adults and nymphs, syrphid fly larvae and cecidomyiid fly larvae.  Several fungal pathogens will also help to keep populations under control.

Period of Activity
Aphids are present throughout most of the growing season.  However, populations build quickly during hot, dry weather.  Many natural control agents, such as parasitic fungi are limited in hot, dry weather conditions, allowing aphid populations to increase rapidly.

Scouting Notes
Examine 10 sets of 10 plants per field.  Look for developing colonies on the ears and tassels.  A plant with more than 20 aphids is considered infested.  Take note of whether population levels are increasing from week to week.

Thresholds
10% of ears infested (ears with more than 20 aphids are considered infested).

Management Notes

  • The continuous use of broad-spectrum insecticides may disrupt beneficial insect populations, resulting in aphid resurgence.
  • In the early stages (pre-tassel) of corn development, aphid control is not usually necessary.
  • On fresh market varieties, control is warranted if high numbers of aphids are present on the tassels or silks prior to pollination or if populations on the ears begin to increase.